Build Your Own AR-15: A Complete Guide

AR-15 Expanded partsIf you want to build your own AR-15 you’re in the right place. And since you can’t just wave a wand and say “build ar15”, I’ll help guide you through the VAST number of options so you know what really matters…

…and what really doesn’t.

I’ve built a bunch of AR-15s, I come from a family of engineers (I’m designing rifle in CAD) plus I have a passion (bordering on obsession) for research.  I’m putting all that research and experience to good use for you.

So without further ado, let’s get started.

Abe’s 3 Rules for Building an AR-15

When you build your own AR-15, keep these simple rules in mind.

  1. Save money on “non-essential” parts
  2. Don’t skimp on Essential Parts
  3. Junk is expensive.

Many AR-15 parts aren’t very important to the guns operation.  The gun still needs them, but they don’t matter too much.  I’ll detail which parts are “non-essential” below.

There are a few essential parts when you build an AR-15.  These parts take most of the wear and should be of excellent quality, even on a budget build.

I wouldn’t skimp on these essential parts.

Cheap junk is expensive because you’ll end up buying the part twice.  (After buying junk the first time, you’ll shell out even more money for a quality part the second time.)


There’s an old saying that “Form Follows Function”.  I truly believe that to be the case so I ask: Why do you want to build an AR-15?

  • Do just think it would be fun?
  • Do you want a range gun?
  • Are you an LEO or Military who wants a combat weapon?
  • Are you planning to hunt?
  • Is it for competition?
  • If so, is it for long range benchrest or fast-moving 3-gun?
  • Are you worried about the zombie apocalypse?
  • Is it for home defense?

The needs of those applications are all different.  Therefore, they would create a slightly different build.  But even though they are all different, they fall into 3 general categories.

Lightweight builds:  These are rifles that fall under 7 pounds when finished, including optics.   They are optimized for quick handling, putting rounds on a target quickly at close-medium ranges.  They are great for hunting, and are favored by LEO and the 3-gun crowd.

General purpose:  The typical AR-15 build includes a vast array of options.  They usually weigh from 7-10 pounds and can fit almost any role imaginable.

Heavy Target:  These AR-15 builds typically have long 24″ plus heavy barrels.   They are only good for benchrest shooting.

Most people I talk to in the gun shop I manage just want a decent general purpose rifle.  Because of that, I’ll be mostly talking about building an AR-15 from that point of view.  I’ll touch on other goals, but general purpose will be the main focus.

Cartridge Selection

Before you can build your own AR-15, you’ll have to decide which cartridge it should shoot. The four most Popular cartridges for the AR-15 are the 5.56 NATO/223 Remington, .300 Blackout, 6.5 Grendel and the 6.8 SPC.

5.56 x 45 NATOThe 5.56 NATO is currently used by the US military, and is the standard AR-15 cartridge. The 5.56 is loaded to higher pressures than, but is othewise is identical to the .223 Remington.  I have an article on why the 5.56 is BOTH the best and worst cartridge for the AR-15.

The 5.56/223 is the least expensive cartridge you can use to build your own AR-15 build. It’s also probably the best choice if this is your first time. 

The 5.56 can also be very effective 300-400 yards with good ammo selection.

However, It drifts a lot in the wind, which hampers longer range shooting.  It also isn’t legal to hunt deer in most states.  Even if it’s legal, it’s not enough bullet unless you are an AMAZING shot.

300 Blackout CartridgeThe .300 Blackout is the most popular alternative to the standard 5.56/223.

It’s consists of a 5.56 necked up to take a 30 caliber (7.62mm) bullet.  With lighter 120-130 grain bullets it is very close to the 7.62×39 cartridge the AK-47 uses.  With heavier 200+ grain bullets, it becomes the ideal cartridge to suppress because it’s subsonic.

However, the heavy bullets and low velocities mean the bullet’s trajectory looks like a rainbow.  Because of that, it’s not much use beyond 150-200 yards.  Inside that range, it’s great for all medium game with the 200+ grain bullets.

Many people use it suppressed for hog hunting.

6.5 GrendelThe 6.5 Grendel uses different magazines and a different bolt than the 5.56/223 or the 300 Blackout.  The 6.5 Grendel is also my favorite cartridge.  It uses a larger case to propel a 6.5mm bullet to 2400-2800 FPS with 100-130 grain bullets.  6.5mm bullets have a high sectional density, and thus lose velocity very slowly.

The 6.5 Grendel is excellent for hunting all medium game.  It has good long range shooting ability thanks to the aerodynamic bullets.  It has good factory ammo (plus some high quality custom stuff) and cheap ammo for plinking.

The 6.5 Grendel is like the multi-tool of AR-15 world.  It’s doesn’t do any one job perfectly, but it does almost everything pretty darn well.

6.8 SPC CartridgeThe 6.8 SPC is another popular AR-15 cartridge.  Remington and elements of SOCOM designed the 6.8 SPC to improve terminal performance out of an AR-15.  By all accounts they succeeded. In many ways, the 6.8 SPC is similar to the 6.5 Grendel. The major difference is the 6.8 has slightly higher velocity, but less aerodynamic bullets.

There is a huge debate raging on the internet between the two.  In fact, more people read my 6.5 Grendel vs 6.8 SPC article than any other page on this website right now.


  • 5.56 NATO: least expensive ammo and components, and it’s effective to ~300 yards with good ammo.
  • 300 Blackout:  Excellent suppressed, shares bolts & magazines with 5.56, expensive ammo, good for hunting, but range limited to 150-200 yards because of bullet drop,
  • 6.5 Grendel: Excellent “do all” cartridge. good for hunting, long range target, plinking, combat, and most other situations you’d find yourself in. However, it has more expensive components, and ammo is mostly online.
  • 6.8 SPC: Everything I just said about the 6.5 Grendel applies here as well.  (except the long range target shooting)  It’s a very versatile cartridge.


Build your own AR-15: Parts selection.

FYI: If you buy after clicking most of the product links on this page, I'll make a few pennies out of each dollar you spend.  It's not much, but it keeps the website going and I would appreciate your support. 🙂

The Barrel

The Barrel determines the accuracy of the rifle and velocity of the bullets. It also has a huge effect on its balance and weight.

Barrel length

Longer barrels mean faster bullets, but there is a point of diminishing return.

5.56 Barrel Length vs Velocity

The above chart is from a great test on 5.56 barrel length vs velocity.  The ammo used was M855 (62gr “green tip” with steel penetrator) The M855 was designed around a 20″ barrel, and it’s no surprise that it yields the best velocity.

However, a 16″ barrel (the shortest you can legally go without ATF approval) isn’t much slower.  The 16″ barrel will also be lighter and better balanced than a longer barrel.  You sacrifice ~50 yards of effective range and some additional bullet drop and drift if you build your own AR with a 16″ vs a 20″ barrel.

For home defense or LEO/military, a 16″ barrel is ideal because it is lighter and easier to maneuver inside.

It’s worth mentioning that both 300 Blackout and 6.8 SPC don’t benefit as much from longer barrels.  A 16″ barrel gets the vast majority of velocity, and anything longer isn’t helping much.

Barrel Contour/Profile

Build AR15 Barrel Contour OptionsThere are several different options for the profile/diameter when you build your own AR-15.

Lighter barrels obviously create a lighter weapon, but more importantly they create a more balanced weapon.  A well balanced 8 pound rifle will feel lighter and handle more quickly than a poorly balanced 6 pound rifle.

Lighter is just a nice bonus.

I have a personal bias toward lightweight, fast handling rifles, so a “lightweight contour” is the heaviest I would personally go when I build an AR-15.


Lightweight barrels do have a downside.  When barrels heat up from firing a lot of rounds, the metal expands.  If it doesn’t expand evenly, the barrel temporarily warps until it cools back down.  This warping can change the bullet’s point of impact. (But only until the barrel cools down.)

The thicker the barrel, the less this expansion affects the bullet’s point of impact.  Thinner barrels tend to have the bullet’s point of impact drift more.  By more, I’m talking 1-2 inches at 100 yards for a decent barrel.

(Just to be clear, the quality of the barrel is more important than the thickness.  A high-quality featherweight barrel will shift impact very little.)

Lighter barrels do heat up faster, but they also cool down faster.

If you plan to carry the rifle for any length of time, a medium contour (also called a “SOCOM contour”) or the USGI “M4 contour” is the heaviest I would go.  That’s partially for weight reasons, but mostly because of balance.  Heavier barrels are very front-heavy even when short.

Benchrest shooters will favor the heavy and bull contours.

Gas System Length

There is a tiny hole in all AR-15 barrels.  The distance from the breach face to this hole is the gas system length.

This hole lets a tiny amount of the high pressure gas escape the barrel, travel through the gas tube and operate the action.  As long as the bullet is in the barrel, the pressure will remain high.  The instant the bullet leaves the barrel, the pressure drops.

If the gas hole is too close to the muzzle, the pressure will drop too soon and reliability will suffer.  If the gas hole is too far from the muzzle, then the action will operate very violently.  This will cause premature wear on the parts, and can lead to extraction problems.

When you build your own AR-15, you need to pick the right gas system length for your barrel length.

  • 14.5″ barrels (with pinned flash hider to be NFA legal) should use a Carbine Length gas system.
  • 16″ barrels should use a Mid-Length Gas System.
  • 18″ barrels can use either Mid-Length or Rifle length.  The rifle length will feel smoother and softer.
  • 20″ barrels (and longer) should use a rifle length gas system.

You can get plenty of 16″ barrels with a Carbine Length gas system.  They do work, but I would avoid them because they are harder on the rifle than a mid-length.

Barrel Material and finish

You can spend a LOT of time fussing over barrel materials when you build an AR-15.  I prefer to fret over how the barrel is finished.

Mil-Spec barrel material is 4150 steel.  A lot of people use the cheaper 4140 steel which works fine, it just wears more quickly. Stainless steel is also often used, and it works fine too.  For the finer points of barrel material, I’ll refer to MR Guns-n-gear’s video on the topic.

However, more important is how the barrel is finished.

The outside finish is mostly irrelevant because standard parkerizing is plenty corrosion resistant enough unless you store your rifles in a swimming pool.

Inside the bore, the two most popular finishes are Chrome plating and Nitride/Melonite.  Both greatly increase the life of the barrel and prevent corrosion.  I wouldn’t worry too much about the material when you build your own AR-15.  The finish will end up making more of a difference anyway.

It almost goes without saying that better made barrels will be more accurate.

Unfinished barrels are popular because they’re cheap.  They work perfectly fine, but don’t last as long.  Maybe “only” 5000-10,000 rounds as opposed to 15,000 to 30,000.

Barrel Feed Ramps

Build an AR-15 feed ramps

Picture borrowed from

The feed ramp’s job is to help guide the bullet into the chamber.

Originally, they were only on the barrel extension. The military discovered that in full auto fire, the weapon ran more reliably if the feed ramp extended into the Upper receiver slightly.

This change showed up on the M4 and became known as “M4 feed ramps”.

Technically, M4 feed ramps are a better choice when you build an AR-15.  Fortunately, most barrels and Upper receivers have M4 style feed ramps these days.

But as long as the feed ramps on your barrel match the ones on your receiver, I wouldn’t worry about it.


You can find a selection of barrels to suit your needs here.


Advanced Plating and Coating

There are many treatments that can be applied to the “essential” parts that improve their performance. Certain platings make parts last longer, resist corrosion/rust, and make the gun more reliable.  Best of all…

They’re easier to clean.

Cleaning an AR-15 is a nasty affair.  They get incredibly dirty and the carbon gets caked on in places. (the tail of the bolt especially.Thanks to the plating on my Bolt,  I can clean it with a dry paper towel…  and nothing else.

Nickel-boron (also called NIB-X), Nickel-Teflon, Nitride/Melonite, and chrome plating are the best and most common finishes.  Nickel-Boron and Nickel-Teflon are probably the best to use when you build an AR-15, but Nitride/Melonite and Chrome plating are pretty good too.

On a Bolt Carrier Group, the standard Parkerized finish is tried, true, and cheap.  It’s MUCH harder to clean, but it will work as long as you keep it clean and well oiled.

The Bolt Carrier Group

Build AR15 Bolt Carrier GroupThe Bolt carrier Group (or BCG) is the heart of your AR-15 build. It is easily the most important part of the rifle and should be high quality even on a budget build.  If you’re tempted to buy cheap, just remember this.

The bolt is the only thing standing between your body and a small explosion. So, buy a cheap BCG at your own risk. 

There are several different metals that can be used for the bolt (talking about the bolt only, not the bolt carrier).  The military requires “Carpenter 158” steel as the bolt material.  When in doubt, that’s an excellent and safe bet.  9310 steel is also good.

The heat treatment actually makes just as much difference as the steel used.  I would make sure it’s from a reputable company because that’s the best way to ensure proper heat treatment.

I would avoid the 8620 bolts when you build an AR-15. They are cheaper, but also not quite as strong.

There is one last thing to look for on the bolt.  They should be marked “HPT” or “MPI”; preferably both.  “HTP” stands for High-pressure tested, MPI stands for “Magnetic Particle Inspected”.   There are both quality control methods which ensure you’re getting a quality bolt.

A bonus is a bolt that’s “Shot Peened”.

Shot peening relieves the manufacturing stress to slightly increase the strength of the bolt.  It’s a good thing, but not required.

Mil-spec for the bolt carrier is 8620 steel, but the carrier material is less important than the bolt.  If you find someone selling a good bolt, they’re almost certainly selling a good carrier to go with it.

Shrouded vs Ushrouded Firing pin.

Shrouded vs Unshrouded AR-15 Firing Pin

The BCG on the left has a “unshrouded” firing pin.  The BCG on the Right has a Shrouded firing pin.

When the bolt carrier moves to the rear, it cocks the hammer.

on an unshrouded firing pin, the firing pin itself cocks the hammer. This causes a LOT of stress on the firing pin and can cause premature firing pin breakage.  On a shrouded firing pin, the carrier takes the force instead of the firing pin.

Any “full auto” or “m16” BCG will have a shrouded firing pin.

Lastly, The BCG is where I’d spend the extra coin for a high-tech plating.  (Nickel-Boron, Nickel-Teflon, etc)  You’ll thank me when cleaning time comes.

Remember the BCG is the heart when you build your own AR-15.  It should be treated as such.

Here is a good BCG with Nickel-Boron Plating.  And another good BCG with the Mil-Spec Phosphate coating and option for Nitride finish.

Upper Receiver

AR-15 Stripped Upper ReceiverThe BCG and charging handle slide inside the Upper receiver, making it one of the highest wear parts on the whole rifle.

There are two important features you should look for in an upper receiver. First, it should be forged.  Forging is a process which involves heating and then repeatedly hammering the metal to compress it’s structure.  This increases the strength of the metal.

Simply put, forged receivers are stronger than billet receivers.

Billet receivers aren’t exactly weak, but they aren’t as strong as forged receivers.  A properly finished billet receiver will work just fine.

Most importantly, The Upper Receiver must have the proper finish applied.

One of the most important things when you build your own AR-15 is to make sure your parts are finished correctly.  The proper finish is specified as “MIL-8625 Type 3 Class 2” hard coat anodizing.  The “class 3” means Hard-Coat anodizing, which is very durable.  Class 2 means it has a color, instead of class 1 which is clear.

If it the finish is anodizing and its not Type 3, I wouldn’t buy it.

The first upper I bought actually had the finish come off the inside (where it contacted the BCG). Don’t make my mistake and forget that the Upper Receiver is a critical component.

Some companies finish their receiver correctly, but simply don’t list it as Type 3.  I often go the manufacture’s website to check if it’s not specified by a retailer.  I prefer to walk on the safe side and make sure the finish is correct when I build an AR-15.

There are companies which use other finishes (like nickel-boron) for their upper receivers.  It’s overkill, but that’s not necessarily a bad thing.

Here are two high-quality options. One Upper without parts kit, the other Upper with a parts kit installed.  If you get it without the upper parts installed, make sure you also get an upper parts kit.

Charging Handle

BCM Gunfighter Charging HandleThe first time I built an AR-15, I used a cheap charging handle.  After charging the weapon about a dozen times, the entire rifle locked up and would only go halfway back.  A little looking revealed the culprit: The charging handle.

The finish had worn off and was causing it to bind.

Lesson learned.

The charging handle is another place that’s quite important.  Again, you’re looking for MIL-8625 Type 3, class 2 anodizing.  It’s also fine if some of the advanced coatings are used.  In fact, I’d prefer it.  But they aren’t necessary.

Two more things.

First, 7075 Aluminum is better than the cheaper (and weaker) 6061 aluminum.  Also a forged Charging handle is also better (stronger) than an extruded one.

However, I’ll take a properly finished 6061 extruded charging handle over badly finished handle of any type. 

When you build your own AR-15, remember that the coatings and surface finishes are VERY important.  Properly finished anodized aluminum works perfectly…  but it must be properly finished.

This Charging Handle is one of the best on the market, and it’s not overpriced. (I prefer the size medium latch).

Lower Receiver

AR-15 Stripped Lower ReceiverBelieve it or not, the Lower receiver is one of the LEAST important parts of AR-15 build.  Properly finished with MIL-8625 Type 3, class 2 hard coat anodized is the only requirement.  Even then, that’s only because of the trigger and hammer pins.

Forged is better, but not strictly speaking necessary.

I would recommend getting this from your local gun shop.  You’ll avoid shipping and transfer fees, plus you’ll be helping a local business.

Buffer Tube

Much like the Upper Receiver and the Charging handle, the most important thing here is MIL-8625 Type 3, class 2 hard coat anodized.  Most of the buffer tubes sold today are extruded 6061 aluminum instead of forged 7075 aluminum. (Forged 7075 is mil-spec.)

That really isn’t a problem.

Most of us aren’t going to put our lives on the line with these weapons.  As long as it has type 3 anodizing, I wouldn’t worry too much.  If you’re life will be on the line, I recommend the ALG Defense True Mil-Spec Buffer tube kit.

Again, the finish is just as important as the material in most cases.

Mil-Spec vs Commercial Buffer Tube

I’ll make this one simple (and a long story short.)Build AR15 Mil-Spec vs Commercial Buffer tube

When you build your own AR-15, get a Mil-spec Buffer tube.

You can easily recognize Commercial buffer tubes by the slanted back.  They are also larger in diameter by about 0.040″ of an inch. (40 thousandths or about 1 millimeter)

They are made differently, hence the different dimensions.  Again, long story short commercial tubes are slightly weaker but cheaper to make.  Mil-spec are stronger, though slightly more expensive to make.

They make stocks for both, but they aren’t interchangeable.

Commercial stocks on a mil-spec buffer tube will be very wobbly.  Mil-spec stocks won’t fit on a commercial buffer tube.  They make many stocks in versions for both types.  However, some excellent options are only available for a Mil-spec buffer tube.

Why limit yourself when Mil-spec is stronger and has more options?

That’s my opinion anyway.

Buffer Spring

There are two different types of AR-15 buffer springs; the Rifle length and the Carbine length.  The rifle length only works in an A2 style fixed stock.  All AR-15s with adjustable stocks use the carbine length buffer spring.

Buffer springs are commonly made from two different materials: Stainless Steel and Chrome Silicon.  Stainless steel springs are mil-spec.  They are a good choice because of their low cost and excellent corrosion resistance.  Chrome silicon springs are popular because they claim a much longer service life.

Honestly, which one you use doesn’t matter too much.

Chrome silicon might last a lot longer, but it’s also a lot more expensive.  The military has used stainless steel springs for over fifty years and they are proven to work well.  Plus, they’re much less expensive.

Buffer weight

The buffer prevents the Bolt carrier group from moving too far to the rear, which would damage either the BCG or lower receiver.

It also adds weight to the BCG, which controls how quickly the bolt unlocks. Buffer weights are made in several different weights for different setups.

Buffer Weights Build your own AR-15

The buffer weight is important when you build your own AR-15.

If the buffer weight is too heavy, the bolt won’t have enough energy to cycle properly.  If the buffer is too light, the bolt will unlock too quickly.  That will lead to extraction problems and increased wear because the BCG is moving too fast.

The proper buffer weight is hard to accurately predict because it also depends on how much gas comes through the gas tube.  The size of the gas hole in the barrel determines how much gas cycles the action.

These buffer weights should work in the vast majority of rifles.

  • Carbine Gas System, 14.5″ barrel – Carbine or H1
  • Carbine Gas System, 16″ Barrel –  H2 or H3
  • Mid-length Gas system 16″ Barrel – Carbine, H1, or H2
  • Mid-length Gas System 18″ barrel – H2 or H3
  • Rifle Gas System 18″ barrel – H1 (carbine or H2 might also work)
  • Rifle Gas System 20″ barrel – H2 or H3

If you are doing your first AR-15 build, I recommend you get a Buffer tube Kit.  It comes with all the buffer components, and you can swap parts out later if you like.


When you build an AR-15, try not to get too overwhelmed by the insane number of stock options. There is only one rule when choosing a stock.

Make sure your Stock matches your Buffer tube.

Commercial buffer tubes need commercial stocks.  Mil-spec buffer tubes need mil-spec stocks. A2 stocks…  well you get the idea.

One thing to consider is the weight of your stock.  If you are making a lightweight rifle, you can get a stock that’s too light and throws off the balance of the rifle.

The only other thing to keep in mind is that Limbsaver makes a good recoil pad for AR-15s.  They have one version that slips on over the standard El-cheapo AR-15 stocks that come on low-end AR-15s.  And another version (bottom option) that fits on most Magpul stocks.

You can find a good selection of stocks here.

Lower Parts Kit

Build your own AR-15 lower parts kitThere are a lot of little pieces that need to be installed in the lower receiver to build an AR-15.  Fortunately, they come in handy little kits so you don’t have to buy them all individually.

I would use any lower parts kit from a reputable company with a recognized name.

There’s no fancy platings or coating to sort out here, and there’s very little that separates the parts kits from one company to another. (Except for triggers, but I’ll get to that.)

I’ve used CMMG, PSA, Rock River Arms, and one other I can’t remember the name of.  All of them worked well.  Some were easier to install, but once installed they all worked well.

Roll Pin Spiral vs c typeOne difference is the higher end parts kits use spiral roll/spring pins versus the cheap “C” type roll pins.  The Spiral pins are both stronger and easier to install.


It really doesn’t matter because the Roll pins in the lower parts kit take almost no load anyway.

Here is a good basic Lower parts kit. You can also get that same parts kit without the trigger group so you can buy a good trigger group separately.

Trigger Group

Mil-Spec trigger build an AR-15The mil-spec trigger group that comes with 90% of Lower parts kits sucks.  I don’t just mean a little either.   A little googling will confirm that virtually every shooter out there hates the mil-spec trigger.

I won’t ding it for its reliability.  It works very well even when it gets dirty.  But it’s not a fun trigger to pull.  For a cheap or budget build, the basic trigger will “get ‘er done”…

But there are better options.

There are two basic types of triggers to choose from when you build your own AR-15:  Single Stage and Two-Stage.

Single Stage Triggers have the same pull weight throughout the entire trigger pull.  The Military trigger is a single stage trigger, however they are roughly made which leads to a LOT or grit, creep and general slop in the trigger pull.

Match grade single stage triggers have no takeup, no creep, and no forgiveness. Once you pull the trigger, they instantly go bang.  This is useful for match and competition style rifles which need to get a lot of lead downrange as fast as possible.

However, for combat, hunting, and home defense applications, I question the wisdom of using a “no creep” match-grade single stage trigger.  Plenty of people do it safely, but I’m personally not comfortable with it.

Geissele SSA Build an AR15Two-Stage Triggers have two distinctly different pull weights during the trigger pull.

The first stage is relatively light.  When you reach the end of the first stage, you hit a “wall” of slightly higher pull weight.  If you pull through the “wall”, the gun will fire.

Two-Stage trigger allow you to “take up the slack” up to the wall so you know exactly when the trigger will break.

By their nature, they are a little more forgiving.

They also have much more sear engagement (because of the additional travel in the first stage). That basically eliminates the possibility of the sear losing it’s grip on the hammer due to a sudden shock or impact.

Personally, I love two-stage triggers and can’t stand single stage.  However, there are plenty of people who are just the opposite.  But that’s one of the best things about building you own AR-15; everyone can pick their own.  There is a huge selection of AR-15 triggers out there, both single and two-stage for you to pick from.

My personal favorite is the Geissele SSA.  I have one on my rifle and it is (in my mind) the perfect trigger.  I hesitated for a long time because of the price, but it was worth every single penny.

If you just want a good basic trigger, I like either of these.  They’re basically cleaned up mil-spec triggers and they’re pretty darn good for the money. The more expensive one has advanced coatings to make it even better/smoother.

Gas Block

Remember I said there was a a small hole in every AR-15 barrel?  Well the gas block goes over that hole to guide the high-pressure gas into the Gas tube. That’s the gas blocks only function.

However, It often performs one of two additional functions.

Front Sight Gas Blocks

A2 Front SightThe picture to the right shows an “A2” style front sight.  This style of front sight also has the mount for the gas tube. Some people prefer the Fixed A2 style when they build an AR-15.

I am not one of them.

There’s nothing wrong with them.  However, they do obstruct your vision when you are using a Reflex sight or scope. Personally, I prefer a Folding Front sight.

There are two ways to mount a folding front sight.  The first is part of the gas block.  The second is attached to a free float rail (which I’ll get to in a minute.)

Low Profile Gas Blocks

Low Profile Gas BlockI bring up Free float rails because they often extend over the gas block and thus require a “low Profile Gas Block”.

You’ll notice how small that gas block is?  They are that small because they often have to fit under free float rails.

In my opinion, Low profile Gas blocks are the way to go because they allow you a HUGE variety of free float rail options when you build your own AR-15.

If you prefer the look of the A2 style, go for it.  However the low profile Gas block will give you a more flexible rifle.

Adjustable Gas Blocks

Adjustable gas blocks control the amount of gas used to cycle the action.  They do this by incrementally closing off the gas port in the gas block.  This allows you to “tune” your rifle for the best possible performance.

They also help control recoil by preventing the Bolt Carrier group and Buffer from slamming onto the end of the buffer tube.  Instead, they can stop under spring pressure alone.  That reduces felt recoil, and more importantly it helps keep the rifle on target for faster follow up shots.

Unfortunately, A good adjustable gas block costs a lot more than a simple non-adjustable gas block.  On a basic AR-15 build, I wouldn’t worry about getting one.  However, if you’re doing a high end build, then I would consider it essential.

If you would like an A2 Style Gas block, you’ll have to hunt around or buy the barrel with it already attached.

You can find a folding front sight gas block here.  A Low profile gas block here, and you can have your pick of adjustable gas blocks here.

P.S. Gas block are usually attached either by the “clamp on” or Set Screw method.  Either works fine, but set screws do put two small dimples in your barrel. (The dimples won’t affect performance in any way though.)

Gas Tube

The gas tube guides the high-pressure gas back to the Bolt carrier group to operate the action.

When you build your own AR-15, this parts matters very little.  Seriously.  As long as the gas tubes are in spec and made of stainless steel, they should work fine.  I suspect these are all made by just a couple companies anyway.

Make sure your gas tube length matches your barrel’s gas system length.

You can get the regular Stainless gas tubes here, or one that’s Melonite finished here.  I don’t think the melonite helps much, but it does make the gas tube black.

NOTE: make sure you get a Gas tube roll pin to attach the Gas tube to the Gas block.

Muzzle Devices

AR-15 Muzzle Devices

Photo from The Truth About Guns’ comparison of muzzle devices. The link is below.

Muzzle devices screw onto the end of your barrel.  They can have a variety of effects depending on what type you get.

This is a HUGE topic I’m going to HIGHLY condense because I’m guessing you don’t want to still be reading this article when you’re eighty.

(My apologies to any Octogenarians reading this)

There are five basic types of Muzzle device you can choose from when you build your own AR-15

  • Flash Hiders: are designed to reduce the flash of light that follows the bullet leaving the barrel.
  • Muzzle Breaks: Are designed to redirect some of the gas backwards to reduce recoil.  They can be very effective, but most muzzle breaks are insanely loud for the shooter and anyone beside or behind them.  They will not make you popular at the range.
  • Compensators: Have slots or holes designed to counter-act the effects of muzzle rise.  Ideally, they prevent he muzzle from moving much (if at all) to enable extremely fast follow up shots.
  • Combo Devices: Are designed to combine the effects of the other 3.  These days, most muzzle devices are some kind of combo.
  • Suppressors: You already know what they do, and they do it well.  Plus, they reduce recoil, eliminate muzzle flash, and even function marginally well as a compensator.  If you have the money and live in a suppressor legal state, they are the best option.

Which one you pick depends on what you will be doing with the rifle.  Suppressors are the best for pretty much everything, but are expensive and require ATF paperwork.

That’s life.

Anyway, for low light situations, flash hiders are the best option because they will help preserve your night vision.  If someone might be shooting back at you (combat) flash hiders will also help conceal your position.

For competition, compensators rule supreme.  Usually, it’s a combo design incorporating a muzzle break for the fastest possible shot recovery.  Flash suppression takes a back seat because it simply isn’t important.

Muzzle breaks aren’t really needed on an AR-15 because the recoil is already very mild.  If you are shooting at a range, they will also make you very unpopular.  I personally don’t see the point using a muzzle break when you build an AR-15.

But that’s just me.

Now, I could point you to some of the best options, but I’d rather give you an amazing resource to pick your own.  The Truth About Guns did an excellent muzzle break comparison, and followed it up with an excellent Flash hider comparison.

I would decide which features are most important to you, then pick one accordingly.

If you aren’t sure what you want on your AR-15 build, I’d recommend going with an A2 flash hider.  It’s standard on military rifles and they work very well as a flash hider.  Plus, they’re so cheap that you won’t regret getting one even if you get rid of it later.  (Don’t forget to get a Crush washer. You’ll need it for proper timing.)


Some people think magazines are an accessory that’s not very important.  Those people are dead wrong.  Bad mags are one of the biggest causes of malfunction in a rifle.  Don’t forget this fact when you build your own AR-15.

Standard capacity mag size for an AR-15 is 30 rounds.  Despite what the media might say, “high capacity” is over 30; not 11.

I would recommend you use these magazines to start.  There are plenty of other magazines that work well, but these are inexpensive are extremely reliable.  I use them on my ~ $2400 AR-15.  (Which took me over a year and a half to afford.  Slow and steady gets it done)

If you don’t like the idea of Polymer magazines, then these magazines are also a great choice.

Free Float Rail (handguard/forend)

AR-15 build Free Float Rail LengthsI consider a Free float rail essential when I build an AR-15 because they improve accuracy.


First a little explanation is in order.  A Free float rail gets it’s name from the fact that it only touches the rifle at one point.  That point is almost universally the barrel nut.

More importantly, a free float rail never touches the barrel. 

When a rifle fires, the force of the bullet causes the barrel to “whip”.  That is, it distorts very slightly back and forth until it returns to its normal straight condition. This oscillation is perfectly normal for rifle barrels, and doesn’t pose a problem.

If the barrel oscillates the same way every time, it can be extremely accurate.

However, if something interferes with the barrel, then it won’t oscillate the same way every time.  Since the essence of accuracy is consistency, anything that changes the barrel’s behavior will reduce accuracy.

The standard plastic AR-15 hand guard touches the barrel at two points, and thus interferes with it’s oscillation. This makes the less accurate.   By contrast, a free floated hand guard doesn’t touch the barrel at all.  This allows the barrel to be as accurate as it can possibly be.

Picking a Free Float Rail

There are several different kinds of free float rails you can use to build your own AR-15.

Free float tubes.  These are not technically rails at all, but merely tubes that give you a place to put your hand.  They usually screw onto the barrel nut.  One downside of these is you basically are forced to use a scope because these tubes rarely have a place to mount a front sight.

AR-15 Quad RailFree Float Quad Rails.  These have military standard 1913 Picatinny rails on all fours sides.  This gives you plenty of space to mount any accessory your heart could wish for.

The downside is that Quad rails are often fairly heavy and aren’t very comfortable to hold. The comfort factor can be helped with some rail covers.  They go over the rail and make it much more comfortable for your hand.

Key-Mod & M-LOK Rails

Instead of using Picatinny rails to mount cool gear, you now have two more options.

KeyMod Rail Section

KeyMod was released in 2012 and was designed as an alternative to Picatinny rails. It succeeded and works well.

It is a “negative space” rail system, meaning items are attached into the key shaped slots instead of a raised portion like the picatinny rail. This reduces weight and makes it more comfortable to hold.

But KeyMod had a small problem. It doesn’t work well in polymer.

When Magpul looked at using KeyMod for it’s polymer accessories, they discovered it wouldn’t work. Since Polymer is basically Magpul’s thing, they designed an alternate system that works well with polymer.

M-LOK RailEnter the M-LOK system.

The M-LOK system basically does the exact same thing as KeyMod.  M-LOK just uses rectangular slots instead of key shaped ones.  However, M-LOK is cheaper to produce and can be used with polymer gear, not just metal gear.

As a matter of personal taste, I think M-LOK also looks cleaner.

KeyMod looks like convenience store shelving to me. (and more than one person has commented on its resemblance to a certain portion of male anatomy.)  I personally find both resemblances distasteful.

Before you decide, you should know that M-LOK is currently outselling KeyMod by almost 3-1.

That’s according to a great article by Matt over at Jerking The Trigger.

Usually, both M-LOK and KeyMod are combined with a picatinny rail. That is, the picatinny is usually on top with KeyMod or M-LOK on the other sides.  This allows easy mounting of optics, up top, and easy mounting of gear everywhere else.

You can find KeyMod rails here, M-LOK rails here, and Quad rails here.

P.S. Free Float rails usually come with their own barrel nut.


One thing I see missing from most build your own AR-15 articles is a discussion of tools.  Specifically, the ones you’ll need to put your rifle together.

Many people reading this will already have the common tools needed (punches, small hammer, vise, etc).  These people will just want the tools that are needed specifically to build your own AR-15.  You can get a set of those tools here.  (You may not need the armorer’s wrench depending on which free-float rail you go with.)

If you don’t have many tools at all, you’ll also need this set to drive in all the pins.


That’s what you need to know to build your own AR-15.To learn how to assemble it, I suggest you head over to YouTube and search “how to build an AR-15”.  (I’m 100% serious, that’s how I did my first one)

Also, you might notice I didn’t cover sights or optics in this article.  That’s because I already have an article on how to pick the best optic for your AR-15.

I hope this was helpful to you and Happy Building!



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