<P> The means of measuring a rifled bore varies, and may refer to the diameter of the lands or the grooves of the rifling . This is why the . 303 British, named for the bird diameter across the lands, actually uses a . 311 - in bullet (7.70 mm vs. 7.90 mm), as bullet diameter matches the diameter across the grooves . Meanwhile, the . 308 Winchester is measured across the grooves and uses a . 308 - in diameter (7.82 - mm) bullet; the military - specification version is known as 7.62 × 51mm NATO, so called because the bore diameter measured between the lands is 7.62 mm, and the cartridge has a case 51 mm long . </P> <P> The following table lists some commonly used calibers where both metric and US customary are used as equivalents . Due to variations in naming conventions, and the whims of the cartridge manufacturers, bullet diameters can vary widely from the diameter implied by the name . For example, a difference of 0.045 in (1.15 mm) occurs between the smallest and largest of the several cartridges designated as ". 38 caliber". </P> <Table> Common calibers in inch and their metric equivalents <Tr> <Th> Inch caliber </Th> <Th> Metric caliber </Th> <Th> Typical bullet diameter </Th> <Th> Common cartridges </Th> <Th> Notes </Th> </Tr> <Tr> <Td>. 172 </Td> <Td> 4 mm </Td> <Td> 0.172 in </Td> <Td>. 17 HMR, . 17 Hornet, . 17 Ackley Hornet, . 17 Winchester Super Magnum, . 17 - 32 Magnum, . 17 VHA, . 17 Remington, . 17 / 222, . 17 Mach III - IV, . 17 Ackley Improved Bee, . 17 - 357 RG, . 17 Remington Fireball, . 17 Incinerator, 4.39 × 39Rmm SPS </Td> <Td> </Td> </Tr> <Tr> <Td>. 20, . 204 </Td> <Td> 5 mm </Td> <Td> 0.204 in </Td> <Td>. 204 Ruger, 5mm Remington Rimfire Magnum </Td> <Td> </Td> </Tr> <Tr> <Td>. 221 </Td> <Td> 5.45 mm </Td> <Td> 0.221 in </Td> <Td> 5.45 × 39mm Russian family </Td> <Td> Russian Mil Std </Td> </Tr> <Tr> <Td>. 22 </Td> <Td> 5.6 mm </Td> <Td> 0.223 in </Td> <Td>. 22 Short, . 22 Long, . 22 Long Rifle, . 22 Stinger, 22 Extra Long, . 297 / 230 Morris Extra Long, . 22 Hornet, . 22 Rem Automatic, 5.66 x39 MPS, . 22 Rem Jet </Td> <Td> </Td> </Tr> <Tr> <Td>. 224 </Td> <Td> 5.7 mm </Td> <Td> 0.224 in </Td> <Td>. 218 Bee, . 219 Zipper, . 22 Hornet - K, . 220 Swift, . 222 Remington, . 222 Remington Magnum, . 223 Remington, 5.56 × 45mm NATO, 5.7 × 28mm, . 22 TCM, 5.8 × 42 Chinese, . 224 Weatherby Magnum, . 225 Winchester, . 223 Winchester Super Short Magnum (Obsolete). 223 Ackley Improved, . 219 Donaldson Wasp, . 221 Remington Fireball, . 22 - 250 Remington and many more </Td> <Td> </Td> </Tr> <Tr> <Td>. 243 </Td> <Td> 6 mm </Td> <Td> 0.243 in </Td> <Td>. 243 Winchester, . 244 Remington, 6mm Remington, 6 mm plastic airsoft BBs, 6mm Whisper, 6mm PPC, 6mm Bench Rest Remington, 6 × 45mm, 6 × 47mm, 6mm Cheetah, . 240 Weatherby, 6 × 62 Freres, 6mm Norma BR, 6XC Tubb, 6mm JDJ, 6mm SAW, 6 - 250 Walker, 6.17 Spitfire, 6.17 Flash, 6mm Lee Navy, and more, </Td> <Td> </Td> </Tr> <Tr> <Td>. 25 </Td> <Td> 6.35 mm </Td> <Td> 0.257 in, 6.35 mm </Td> <Td>. 25 ACP (0.251 "), 250 / 3000 Savage, 257 Roberts, 25 - 06 (0.257"), </Td> <Td> also called . 25 Auto and 6.35 mm Browning </Td> </Tr> <Tr> <Td>. 26 </Td> <Td> 6.5 mm </Td> <Td> 0.264 in, 6.7 mm </Td> <Td> 6.5 × 55mm, . 260 Remington, 26 Nosler, 6.5 Creedmoor, 6.5 x47 Lapua </Td> <Td> cartridges commonly known as' 6.5 mm' </Td> </Tr> <Tr> <Td>. 27 </Td> <Td> 6.8 mm </Td> <Td> 0.277 in, 7.035 mm </Td> <Td>. 270 Winchester, 6.8 SPC </Td> <Td> </Td> </Tr> <Tr> <Td>. 284 </Td> <Td> 7 mm </Td> <Td> 0.284 in, 7.213 mm </Td> <Td>. 280 Remington, 7mm - 08 Remington, 7mm Remington Magnum, 7 × 57mm Mauser, 7 × 64mm </Td> <Td> commonly called' 7 mm' </Td> </Tr> <Tr> <Td>. 308 </Td> <Td> 7.62 mm </Td> <Td> 0.308 in, 7.82 mm </Td> <Td>. 30 Luger (7.65 × 21mm Luger), . 30 - 30 Win, 30 Herrett, . 300 Whisper, . 30 - 378 Weatherby, 7.63 Mannlicher--Schoenauer, 7.63 Mauser, . 30 USA Rimless, . 308 Corbon, . 3 - 9 Savage, . 30 Kurz, 300 AAC Blackout (7.62 × 35mm), 7.5 mm Schmidt--Rubin, . 300 Winchester Magnum, . 30 Carbine, 309 JDJ, . 30 - 03, . 30 - 06 Springfield, . 30 - 06 JDJ, . 307 GNR, . 308 Winchester (7.62 × 51mm NATO), . 300 Weatherby Magnum, . 30 Army (. 30 - 40 Krag), 7.82 mm Lazzeroni, and dozens more </Td> <Td> </Td> </Tr> <Tr> <Td>. 311 </Td> <Td> 7.9 mm </Td> <Td> 0.311 in, 7.92 mm </Td> <Td>. 303 British, 7.62 × 39mm Soviet, 7.62 × 54mmR, 7.62 × 25mm, 7.7 × 58mm </Td> <Td> 7.62 × 54mmR is actually 7.92 mm (Mosin, SVD, PKM, etc .) The same applies to 7.62 × 39mm (AK - 47, AKM, etc .) </Td> </Tr> <Tr> <Td>. 312 </Td> <Td> 7.94 mm </Td> <Td> 0.312 in, 7.94 mm </Td> <Td>. 32 ACP </Td> <Td> Also known as 7.65 × 17 mm Browning </Td> </Tr> <Tr> <Td>. 323 </Td> <Td> 8 mm </Td> <Td> 0.323 in, 8.20 mm </Td> <Td> 8 × 57mm IS, . 325 WSM, 8mm Remington Magnum, 8 mm plastic (airsoft) BBs </Td> <Td>. 32 caliber rifle cartridges </Td> </Tr> <Tr> <Td>. 338 </Td> <Td> 8.6 mm </Td> <Td> 0.338 in </Td> <Td>. 338 Lapua, . 338 Norma Magnum, . 338 Winchester Magnum, . 338 - 378 Weatherby Magnum </Td> <Td> C14 Timberwolf (Canadian Forces) </Td> </Tr> <Tr> <Td>. 355 </Td> <Td> 9 mm </Td> <Td> 0.355 in </Td> <Td> 9mm Luger, 9mm Ultra, 9mm Bayard Long, 9mm Browning Long, 9mm Mauser, 9mm Winchester Magnum, 9mm Glisenti, 9 × 21mm, 9 × 23mm Winchester, 9mm Mi - Bullet, 9mm Steyr, . 356 Team Smith & Wesson, 9mm Federal, 9mm × 25mm Dillon, 9mm Action Express </Td> <Td> </Td> </Tr> <Tr> <Td>. 356 </Td> <Td> 9 mm </Td> <Td> 0.356 in </Td> <Td>. 380 ACP (9mm Short), 9 × 56mm Mannlicher--Schoenauer, 9mm × 57mm Mauser </Td> <Td> </Td> </Tr> <Tr> <Td>. 357 </Td> <Td> 9 mm </Td> <Td> 0.357 in </Td> <Td>. 38 Super, . 38 Special, . 357 Magnum, . 357 SIG, . 35 Remington </Td> <Td> Handgun cartridges known as "38" are . 357 caliber . Generally . 357 for revolvers and rifles, . 355 in autoloaders </Td> </Tr> <Tr> <Td>. 363 </Td> <Td> 9 mm </Td> <Td> 0.363 in </Td> <Td> 9 × 18mm Makarov </Td> <Td> </Td> </Tr> <Tr> <Td>. 365 </Td> <Td> 9.3 mm </Td> <Td> 0.365 in </Td> <Td> 9.3 × 62mm, 9.3 × 64mm Brenneke, 9.3 × 72mmR, 9.3 × 74mmR </Td> <Td> </Td> </Tr> <Tr> <Td>. 375 </Td> <Td> 9.5 mm </Td> <Td> 0.375 in, 9.53 mm </Td> <Td>. 375 H&H Magnum, 9.5 × 57mm Mannlicher--Schönauer (. 375 Rimless Nitro Express (RNE) × 21⁄4) </Td> <Td> </Td> </Tr> <Tr> <Td>. 40 </Td> <Td> 10 mm </Td> <Td> 0.400 in </Td> <Td>. 40 S&W, 10mm Auto </Td> <Td> </Td> </Tr> <Tr> <Td>. 44 </Td> <Td> 10.9 mm </Td> <Td> 0.429 in </Td> <Td>. 444 Marlin, . 44 S&W Russian, . 44 S&W Special, . 44 Remington Magnum, . 44 Auto Mag, . 440 Cor - Bon, . 44 / 454 JDJ Woodswalker </Td> <Td> </Td> </Tr> <Tr> <Td>. 45 </Td> <Td> 11.43 mm </Td> <Td> 0.451--0.454 in </Td> <Td>. 45 ACP, . 45 GAP, . 454 Casull, . 45 Long Colt, . 455 Webley </Td> <Td> Bullet diameter depends on bullet type / material . Generally 0.451 in for full metal jacket bullets and 0.454 in for lead bullets . </Td> </Tr> <Tr> <Td>. 50 </Td> <Td> 12.7 mm </Td> <Td> 0.510 in, 12.95 mm </Td> <Td>. 50 BMG, . 50 Action Express, 12.7 × 108mm </Td> <Td> M2 Browning machine gun and other heavy machine guns, long - range rifles typified by Barrett products . Desert Eagle handgun . </Td> </Tr> </Table> <Tr> <Th> Inch caliber </Th> <Th> Metric caliber </Th> <Th> Typical bullet diameter </Th> <Th> Common cartridges </Th> <Th> Notes </Th> </Tr>

What's the difference between .40 and .45 caliber
find me the text answering this question