by Frank Moss

Here is a guide to ammunition calibers and their imperial or metric sizing.

Inch Caliber

Metric Caliber

Typical Bullet Diameter

Common Cartridges


.20, .2045 mm0.204 in.204 Ruger, 5 mm Remington Rimfire Magnum
.225.56 mm0.223-0.224 in.22 Long Rifle, .222 Remington, .223 Remington, 5.56×45mm NATO, 5.7 x 28 mm, .22-250 Remington, .22 Airgun
.246 mm0.243 in.243 Winchester, 6 mm Remington
.256.35 mm0.25 in, 6.35 mm.25 ACP, 6.35x16mmSRa.k.a. .25 Auto and 6.35 mm Browning
.266.5 mm0.264 in, 6.7 mm6.5 x 55 mm, .260 Remingtoncartridges commonly known as 6.5 mm
.276.8 mm0.277 in, 7.035 mm.270 Winchester, 6.8 SPC
.287 mm0.284 in, 7.213 mm.280 Remington, 7 mm Remington Magnum, 7 x 57 mm, 7mm-08 Remington, 7 x 33 mm Sakocommonly called 7 mm
.307.62 mm0.308 in300 AAC Blackout, 30-06, .308 Winchester (7.62x51mm NATO), .300 Winchester Magnum, 7.82 Lazzeroni PatriotAmerican “.30 caliber”
.3037.62 mm0.311 in – 0.312 in.303 British, 7.62×39, 7.62x54R, 7.62×25Other “.30 caliber”, note the mis-labelling of the Russian “7.62” rounds where neither the bore nor the groove diameter is 7.62mm
.3238 mm0.323 in8x57mm IS, .325 WSM, 8 mm Remington Magnum.32 caliber rifle cartridges
.3579 mm0.355-0.357 in.38 Special, .380 ACP, .357 Magnum, .357 SIG, .35 Remington, 9×19mm Parabellum, 9x18mm MakarovHandgun cartridges known as “38” are .357 caliber. Generally .357 for revolvers and rifles, .355 in autoloaders
.4010 mm0.400 in.40 S&W, 10 mm Auto
.4511.43 mm0.450 in.45 ACP, .45 GAP, .454 Casull, .45 Long Colt
.5012.7 mm0.510 in (12.95 mm).50 BMG, 12.7 x 108 mmM2 Browning machine gun and other heavy machine guns, long range rifles typified by Barrett Firearms Manufacturing products




About The Author

Well traveled in Europe and North Africa, Frank Moss has lived in England, Germany and Italy thanks to sabbaticals taken by his father, an award winning physicist. Notable positions held during his almost 20 year IT career are founding engineer of IBM's SmartCloud, Cloud Architect for SPAWAR, and Cloud Architect for CenturyLink's FedRAMP Cloud Project. He specializes in architectural security compliance (secure by design) and holds a C|EH. When not working, Frank enjoys outdoor activities, shooting, camping and spending time with his wife and children. You can find Frank at one of his two sites: surviveseptember.com or nine13tech.net

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