Decoding Bullet Calibers: An Informative Guide to Firearm Ammunition

Decoding Bullet Calibers: An Informative Guide to Firearm Ammunition

Understanding Bullet Calibers

Gun enthusiasts often get confused because there are two different ways to measure the bore diameter of a cartridge: one in inches (the caliber system) and the other in millimeters. This page is here to make things clear regarding bullet calibers.

Inches vs. Millimeters

Ammunition makers haven’t exactly made it easy to understand. But we’ve put together a simple resource to show you the equivalent measurements in millimeters and inches (caliber) so you can quickly grasp the differences. Even if you’re an experienced shooter, looking at some of those conversions can be mind-boggling.

The .308 Winchester Dilemma

As an example, take the .308 Winchester. It’s called that because the bullet is .308 inches in diameter. In metric, that’s 7.82 millimeters. But it’s often known as a 7.62 caliber due to its military background. The reason for the difference is that one measurement counts the space between the grooves inside the barrel, while the other considers the space to the raised part of the barrel. To add to the confusion, the .308 is often labeled a .30 caliber, which isn’t quite accurate.

Clearing Up the Confusion

Cartridge	Caliber
.17 Hornet	0.172
.17 WSM	0.172
.17 HMR	0.172
.204 Ruger	0.204
.22lr	0.223
.220 Swift	0.224
.224 Valkyrie	0.224
.22-250	0.224
.22 Nosler	0.224
.22 Creedmoor	0.224
.22 WMR	0.224
.223 / 5.56	0.224
.22 Hornet	0.224
.222 Remington	0.224
.243 Winchester	0.243
6mm BR	0.243
.240 Weatherby Magnum	0.243
6mm Remington	0.243
6mm Creedmoor	0.243
.25-06 Remington	0.257
.257 Weatherby Magnum	0.257
6.5 Creedmoor	0.264
6.5 PRC	0.264
.260 Remington	0.264
6.5-300 Weatherby Mag	0.264
.26 Nosler	0.264
6.5-284 Norma Match	0.264
6.5 x 55 Swedish Mauser	0.264
.264 Winchester Magnum	0.264
6.5 Weatherby RPM	0.264
6.5 Grendel	0.264
.270 Winchester	0.277
.270 WSM	0.277
.270 Weatherby Magnum	0.277
6.8 Western	0.277
6.8 Remington SPC	0.277
.27 Nosler	0.277
7mm-08 Remington	0.284
7mm Rem Mag	0.284
.28 Nosler	0.284
.280 Ackley Improved	0.284
.280 Remington	0.284
7mm Weatherby Magnum	0.284
7 SAUM	0.284
7 STW	0.284
7mm Mauser	0.284
7 WSM	0.284
.308 Winchester	0.308
.300 Winchester Magnum	0.308
.30-06 Springfield	0.308
.300 WSM	0.308
.300 Weatherby Magnum	0.308
.300 PRC	0.308
.300 RUM	0.308
.30-30 Winchester	0.308
.300 Blackout	0.308
7.62 x 39mm	0.308
.30 Nosler	0.308
.300 Ruger (RCM)	0.308
.30-378 Weatherby Mag	0.308
.325 WSM	0.308
.338 Win Mag	0.338
.338 Lapua Magnum	0.338
.338 Federal	0.338
.340 Weatherby Magnum	0.338
.33 Nosler	0.338
.338-378 Weatherby Mag	0.338
.338 RUM	0.338
.350 Legend	0.357
.35 Whelen	0.358
9.3 x 62mm Mauser	0.366
.375 H&H	0.375
.375 Ruger	0.375
.378 Weatherby Magnum	0.375
.416 Ruger	0.416
.416 Remington Magnum	0.416
.416 Rigby	0.416
.444 Marlin	0.429
.450 Bushmaster	0.452
.45-70 Govt	0.458
.458 Win Mag	0.458
.50 BMG	0.51

You can see that naming cartridges can be complicated because manufacturers prefer nice, even numbers and often ignore the precise measurements. The table above simplifies things by making some generalizations. However, to provide the full details of each rifle cartridge’s exact bullet diameter in both inches and metric, we’ve included a separate table.

Conclusion

We hope this resource helps clear up a confusing topic in the world of firearms. Whether you’re a seasoned shooter or a newcomer, understanding bullet calibers is vital for making informed choices. Remember, when in doubt, consult the measurements. Understanding calibers will ensure you choose the right ammunition for your shooting needs.

For more reference here are links to some additional sources.

SAAMI