How To Easily Compare ANY Two Cartridges

Two Cartridges on a Scale for ComparisonI got an email from one of my readers asking me to compare a few cartridges.  I figured it was a good incentive to write an article about it.

This is one of the most misunderstood topics in the gun world, so hopefully I can shed some light on how simple it really is.

First, remember the brass of a cartridge is simply a convenient way to store and ignite the gunpowder.  Nothing more, Nothing less.

It’s the bullet, NOT the cartridge that matters…

Sort of.

Obviously the physical dimensions of the cartridge have a role to play.  (You can’t shoot a 300 Win Mag through an AR-15.)  But it’s less important than you think it is.  Good cartridge design matters, but not to the average shooter.

To compare cartridges, I want to know just 3 things: Bullet diameter, Bullet weight, and Bullet Velocity.

Those three numbers will tell you a LOT about any given cartridge.

(NOTE: I use the terms diameter and caliber interchangeably in this article.)

Bullet Caliber

One thing first.

Caliber does NOT mean cartridge.

9mm in caliber means anything with a 9mm bore diameter.

That would include the 9×18 Makarov, the 9mm Browning long, the 9mm Largo, etc.   It also includes the 9×19 Parabellum (9mm Luger) cartridge which most people mean when they say “9mm”.

If you expand “9mm” beyond the common .355 diameter bullet of the 9mm Luger, it includes over three dozen cartridges which fire bullets between  .351 and .360 inches in diameter. (all of which qualify as being 9mm.)

That includes the .357 Magnum and several rifle cartridges including the  .35 Whelen, and 9×57 Mauser

So, moving on…

The bullet’s diameter lets you know a few basic things.  First, it lets you know the general range of bullet weights available for the cartridge.  For every bore diameter, there is a range of common and effective bullet weights.  See examples below.

(These are just common weights for rifle cartridges. Yes I know you can go lighter or heavier than these ranges)

  • .22 caliber/5.56mm – 40gr – 75gr (lighter in rimfire cartridges)
  • .243 caliber / 6mm –  60gr – 108gr
  • .257 caliber – 70gr – 120gr
  • .264 caliber/6.5mm – 90gr – 140gr
  • .277 caliber/6.8mm – 100gr – 150gr
  • .284 caliber / 7mm – 120gr – 175gr
  • .30 caliber/7.62mm – 150gr – 190gr (up to 220gr occasionally)
  • 8mm – 170gr – 220gr
  • .338 caliber – 200gr – 300g

 

Bullet weight – Heavy vs Light for caliber

When we talk about bullet weight, it’s almost always in respect to caliber.  For example, a 90gr .223/5.56 bullet is extremely heavy for it’s caliber.  However, a 90gr .338 bullet is almost laughably lightweight.

When we talk about “heavy for caliber” or “light for caliber” bullets, what we really mean is Sectional Density.  Sectional Density is a number that tells us how “short and fat” vs. “long and thin” a bullet is.  Higher numbers are longer and thinner.

I have a whole article on sectional density and I HIGHLY recommend you read it because it’s very important for comparing cartridges.

Sectional Density tells us a LOT about how a bullet will behave.

For example:

Heavy for caliber bullets will retain their speed better than light bullets because of inertia.

That brings us to the term Ballistic Coefficient (which is usually abbreviated BC).  BC is a number that tells you how aerodynamic a bullet is; higher numbers are better.

(NOTE: You can compare BC using the G1 or G7 drag models, but it doesn’t matter here.  As long as you compare G1 to G1 and G7 to G7, you’ll do fine.)

If you look at the picture below, which bullet do you think would be more aerodynamic?

308 vs 7mm

The two bullets are in scale, and almost identical in weight. (the 308 is 178gr, the 7mm is 175gr) They are Both Hornady ELD-X bullets, so they have the same construction.

Yet despite having the same weight, one is far more aerodynamic than the other.

The shorter and fatter .308 bullet has a good G1 BC of .552, while the thinner and longer 7mm bullet has an outstanding G1 BC of .689.  The 7mm bullet is MUCH more aerodynamic because the wider 308 bullet has more drag (air resistance) than the slimmer 7mm bullet.

Because they are longer and thinner, heavy for caliber (high sectional density) bullets also penetrate better. (assuming the same construction)

Again, this is common sense: a thin object will penetrate better than a fatter object.

This is where gun owners tend to fly completely off the tracks though.

For some reason, the “Bigger is Better” myth runs rampant in the gun world.  Bigger bullets – i.e. a larger caliber – DO NOT penetrate better.

If you have two bullets with the same weight and construction, the SMALLER caliber bullet will penetrate deeper because there is less resistance. 

This is just common sense and it’s also an important point when comparing cartridges.

However if you get too small, you start losing weight.

For instance, the .243 Winchester is a 308 case necked down to 6mm. It has a great reputation against deer and other medium game.  However, the .243 is limited to bullets in 108gr range because of the small caliber.  I wouldn’t use it on anything larger than deer, but some people have used it to hunt larger game.

Light-for-caliber bullets

On the other side, a lighter bullets can be driven faster with less recoil.  Faster bullets mean a flatter trajectory, and the reduced recoil is nice.

However, lighter weight bullets are affected more by the wind and lose their velocity more quickly.  The reason for both of these is inertia.  Lighter bullets are easier to move because they’re, well…  Lighter.

 

Bullet Velocity

Combined with bullet weight and caliber, velocity also tells you a lot about a cartridge.  One of the most obvious advantages of faster bullets is the flatter trajectory.

However, there is a point of diminishing return, especially for hunting.  Once a rifle bullet is going around 2500 – 2600 fps, you will have plenty of trajectory for hunting.

Faster is better, but only until the bullet is going around 2900fps – 3000fps.

At this point, there’s so much air resistance that the bullet starts losing speed very quickly.   At that point, you are better off going to a heavier (and slower) bullet that’s more aerodynamic.

If you are pushing a heavy for caliber bullet at ~2800-2900 but not getting the performance you want, then it’s time to get a larger caliber.

Barrel Life

Pushing heavy for caliber bullets very fast (around 2900 – 3100 fps or faster) causes your barrel to wear out more quickly.  The heavier and faster the bullet and the smaller the bore, the faster the barrel wears.

On the other hand,  If the cartridge pushes bullets at sensible speeds (2500-2800) the barrels last much longer.

Speed vs. Penetration

In both rifle and handgun bullets, there’s an inverse relationship between speed and penetration with expanding bullets.

In Layman’s terms, faster bullets don’t necessarily penetrate deeper. 

Why?

Because if it’s an expanding bullet, the impact speed decides how fast the bullet expands.  If the bullet expands very quickly because of a high impact speed, the wider (expanded) bullet will have more resistance and thus stop more quickly.

On the other hand, if the bullet is going more slowly it will open up more slowly and not as wide.  Because it takes longer to open and doesn’t open as wide, there is less resistance so it penetrates deeper.

It’s counter-intuitive at a glance, but makes sense once you think about it.

It’s also another good reason to limit your muzzle velocity to around 2800-2900 fps.  Bullets can expand too much and/or start breaking apart on impact.

 

A Word about Hunting

If you are picking a cartridge for hunting, please realize you don’t need a massive bullet to take game.  You need great shot placement.  I say this all the time: You can’t miss fast enough to win a gunfight or fill a hunting tag.

Deer are relatively easy to kill, and almost any centerfire rifle cartridge of 6mm and up is plenty.

For larger game, a sectional density around .250 and a bullet weight around 120+ grains is good.   For truly large game (in North America) a sectional density of ~.280 with at least a 140-150 grain bullet is PLENTY for large game.

Here is a sectional density calculator you can use.

If you want something more concrete, then I suggest you look at the Hornady HITS calculator.  The HITS calculator gives a conservative estimate of the bullet weight, diameter, and impact velocity required to kill game of various weights.  (Notice that decreasing the diameter makes the bullet more lethal.)

Bullet construction/design is very important for hunting, especially larger game.

But as long as you choose a bullet designed for larger game I wouldn’t worry.  If you aren’t sure, a bonded bullet or one of the Barnes all-copper bullets is a good choice.

 

A Word About Recoil

Recoil usually destroys accuracy.

Some people aren’t bothered by it, but the majority of us are. whether its competition, hunting, or combat accuracy matters.  Lower recoil makes shot placement easier.  The number one reason for getting a smaller cartridge is to reduce recoil.

There are four factors that determine recoil:

  • Bullet weight (heavier means more recoil)
  • Bullet velocity (faster means more recoil)
  • The number of grains of powder used (more powder means more recoil)
  • The weight of the gun (lighter guns mean more recoil)

Recoil is measured in ft-lbs.

For comparison, a 5.56 rifle has ~4 Ft-lbs of recoil.  A .308 has about 16-18 ft-lbs of recoil energy.  A 12 gauge shotgun with target loads is around 16-20 ft-lbs depending on the specific load.

 

Putting It All Together

This is what I do to compare different cartridges.

First, I find the caliber, velocity, and bullet weights for a heavy-for-caliber loading in all the cartridges I want to compare.  I like going to Wikipedia to find velocities and bullet weights.  It’s not gospel truth, but it’ll get you close enough very quickly.

For hunting, I would make your next stop the Hornady HITS calculator. It gives a (very) conservative estimate of the bullet weight, diameter and velocity required to kill various game.

In the HITS calculator, a score over 500 is considered enough for deer.  For some scale, 900-1500 hits is considered enough for animals weighing up to 2000lbs.

If your cartridge hits the minimums in the HITS calculator, then you definitely have “enough gun”.  (HITS is pretty conservative.)

This gives you a good basis for comparing how lethal a bullet is.  It’s not an exact science, but it will give you good “ballpark” numbers.  Remember, that shot placement is more important than anything else in hunting.

For target shooting, all that really matters is the bullet’s trajectory and recoil.

This next part is easy, but slightly technical so stay with me. You’ll need to find the sectional density of your chosen Bullet weight.  I use this Sectional Density Calculator.

Now, head over to the Hornady’s Ballistics Calculator.

  • First, In the “basic/advanced” drop down box, choose advanced.
  • Find the “Drag Function” and set it to G7  (NOTE: Using the Sectional Density for the BC value gives you an “ideal” comparison.  If you want actual values, you’ll have to find the BC for a specific bullet.)
  • Set the “Ballistic Coefficient” box value to the Sectional Density of the bullet.
  • Set the wind speed to something reasonable. (I usually use 5 or 10.)
  • Set the bullet’s velocity and weight.
  • Hit calculate.

Write down the drop and wind drift or open a new browser tab.  Then repeat those steps for the other cartridges you are comparing.

You’ll now have a good idea how the bullet’s path will look downrange.

For both hunting and target shooting, don’t forget to factor in recoil.  You can use a recoil table to get ballpark numbers, but it’s easy to get more accurate numbers.  Here is the online recoil calculator I use.

You’ll need to know how many grains of powder are used in that cartridge for a given bullet weight and velocity. You can either use Google or Nosler’s Load Data archive for these numbers. I usually use Nosler because it’s faster.

Plug in the numbers and you you’ll be able to compare recoil for the two cartridges.

Also, don’t forget about barrel life in your comparison.

Google is your only real option to find barrel life. For a hunting gun, it almost doesn’t matter because you’ll probably never shoot the barrel out.

For target shooters and plinkers, higher is better.

 

As an example, lets look at the .308 Winchester family of cartridges.

The four cartridges below all use a .308 Winchester case that’s necked down for the smaller bullets. Comparison is using heavy for caliber bullets except for the 7mm-08, because no one seems to make loaded ammo heavier than 150 grains.

  • .243 Winchester – 108 grain bullet @ 2900
  • .260 Remington – 140 grain bullet @ 2800
  • 7mm-08 – 150 grain bullet @ 2800
  • .308 Winchester – 168 grain bullet @ 2700

I’ve compiled the relevant data into this table.

Note:

CartridgeBullet WeightVelocityRecoil (ft-lbs)HITS500yd HITS500yd Drop
(100yd zero)
500yd Wind Drift
.243 Win108gr29008.9817585-48"16.6"
.260 Rem1402800131125828-50.7"15.7"
7mm-08150280014.31117801-51.9"17.1"
.308 Win168270015.51148802-57.6"19.3"

As you can see, you gain something going from the .243 Win to the .260 Rem.  However, going larger doesn’t increase performance.  In fact, the larger 7mm-08 and .308 have more recoil, more drop and more wind drift than either of the smaller cartridges.

Any of the larger three would be good for hunting large game such as elk.  If you don’t agree that the .260 Remington is enough for game this large, I suggest you read my article on terminal performance.  Or, you could read a wonderful article on Guns America called Busting the Magnum Myth.

Bigger isn’t necessarily better.

 

Conclusion

I’ve been comparing cartridges for years.  In that time, I’ve settled on my favorite bore diameter being either 6mm or 6.5mm depending on the job.

Pistols are not Thor's HammerWith a ~100 grain bullet, a 6mm rifle gives very little recoil and allows you to drop deer-sized game like the hammer of God.

The low recoil makes it perfect for newer, younger, and/or smaller shooters.  Plus, some of the most accurate cartridges ever created are in 6mm which makes it perfect for target shooting.

I also think the right size 6mm cartridge could make an ideal General Purpose Combat cartridge.

If I was doing true long range shooting (600-100 yards) then I would probably pick a 6.5mm cartridge like the 6.5 Creedmore or .260 Remington.  Either is ideal for long range competition.

As an added bonus, a 6.5mm cartridge of that size would allow me to hunt most game that walks in the continental USA if I decided to chase big game.  (never appealed before though so…)

For extreme range shooting beyond 1000 yards, I would probably consider something like the 7mm Rem Mag using 175 grain bullets.  The barrel life is decent if you don’t push it too hard, and a 175 grain bullet @ 2800 only produces ~22 Ft-lbs of recoil in a 8 pound rifle.  It would shoot as flat as a laser beam and there’s no animal in North America that would survive a shot through the boiler room.

But for most people in North America (me included), there’s very little to be gained from a bullet larger than 6.5mm.

Again, bigger doesn’t mean better.

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