Maverick223
Member
...but, the cartridge caliber designation is typically based upon the bore diameter which in the case of .223Rem./5.56NATO is actually pretty close to 5.56mm so that makes sense (at least to me). Same with many others such as .45cal. pistols and rifles, both have a approximately .450in. bore, though they shoot .452in. and .458in. projectiles respectively. In short there is no well accepted naming convention, but by military standards the bore is often the basis for the cartridge designation.I understand that most would use 6mm to designate a .243" bullet, But a 5.56mm is not really 5.56mm it's 5.6896, so it's closer to 5.7mm. .223rem is .224". This could go on and on and on. So 6.17mm = 6.2mm
Fully confused yet?