Thread: 5.56 vs .223
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Old November 29, 2012, 06:59 AM   #14
Bart B.
Senior Member
Join Date: February 15, 2009
Posts: 6,318
Sweetshooter, where in the dickens did you get a basis for this:
.308/7.62—This is different and significant I believe (of course I might be wrong). It depends on origins of the barrel. Some European 7.62 projectiles are "correctly" dimensioned at .312 OD—correct because the rifle grooves are actually 7.92—and may hurt a .30 rifle made for .308 projectiles.
I ask 'cause the 7.62 NATO round's (as well as the .308 Win.) barrel was originally spec'd at .3000" (7.620mm) for bore and .3080" (7.823mm) for groove diameter. The USA's SAAMI bullet diameter spec is .3090" -.0030" (7.849mm -.076mm) and the MIL-SPEC's the same as far as I can determine. Actual bullet diameter's been in the .3070" (7.798mm) to .3092" (7.854mm) range for both commercial and military versions.

Many thousands of Lapua's .3092" diameter 170, 185 and 195 grain FMJRB bullets have been fired in .308 Win. barrels with .299" bore and .3075" groove diameters without incident using max loads. 42 grains of IMR4064 under their 185-gr. version has been used winning many a match setting a few records and it may well be the most accurate load ever tested I know about for the .308 Win. Military rifle teams shooting 7.62 NATO handloaded match ammo at proof load pressures in the 65,000 CUP (80,000 PSI) range in their M1's and M14's never had a safety issue, but I wouldn't recommend such loads in bolt guns.

I've never heard of any 30 caliber bullet nor a 7.62/.308 barrel groove diameter at .312" (7.925mm) diameter. . . .that is until I read your post.

For SAAMI specs:
Pressure and velocity specs start on page 13; find the .223 Rem. & .308 Win. data. .223 Rem. chamber and barrel specs are on page 47. Page 66 has the info on the .308 Win. barrel and chamber dimensions.

For MIL-SPECS for the 7.62 NATO M80 round:

MIL-SPECS for the 5.56 NATO M193 round:

Open the file then go to section 3.7.1 for pressure.

Regarding any pressure number for these cartridges. The SAAMI document explains in detail how their CUP and PSI pressure systems are configured. I don't know if the MIL-SPEC systems are the same. Identical ammo and barrels will get different pressure numbers depending on where the sensor is positioned relative to the cartrige.

Last edited by Bart B.; November 29, 2012 at 08:34 AM.
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