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Old January 30, 2012, 09:04 PM   #11
MR-7-45
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Join Date: October 4, 2005
Location: Central Texas
Posts: 70
.308 and 7.62 mm brass is slightly different. I did some digging around.

7.62x51:
Parent case .300 Savage
Case type Rimless, Bottleneck
Bullet diameter 7.82 mm (0.308 in)
Neck diameter 8.58 mm (0.338 in)
Shoulder diameter 11.35 mm (0.447 in)
Base diameter 11.84 mm (0.466 in)
Rim diameter 11.94 mm (0.470 in)
Rim thickness 1.27 mm (0.050 in)
Case length 51.05 mm (2.010 in)
Overall length 69.85 mm (2.750 in)
Rifling twist 1:12"
Primer type Large Rifle
Maximum pressure 415 MPa (60,200 psi)

.308win
Parent case .300 Savage
Case type Rimless, Bottleneck
Bullet diameter 0.308 in (7.8 mm)
Neck diameter 0.343 in (8.7 mm)
Shoulder diameter 0.454 in (11.5 mm)
Base diameter 0.470 in (11.9 mm)
Rim diameter 0.473 in (12.0 mm)
Rim thickness 0.050 in (1.3 mm)
Case length 2.015 in (51.2 mm)
Overall length 2.800 in (71.1 mm)
Rifling twist 1/12
Primer type Large Rifle
Maximum pressure 62,000 psi (430 MPa)

Same? No but darn close.
Fortunately, the M1A chamber has loose tolerances and will take a .308 casing.
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