Thread: .308 vs .30-06
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Old November 22, 2012, 02:52 AM   #65
Rainbow Demon
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Join Date: September 27, 2012
Posts: 397
Quote:
Match bullets up to 250 grains have been used in .308 Win. chambers with long throats. Muzzle velocity from a 28 inch barrel's about 2150 fps. Needed a 1:8 twist to stabilize them through 1000 yards, but was very accurate when David Tubb used it in the late 1980's.
Would the long throat be due to seating the bullet far beyond the specified cartridge OAL?
If so the cartridge would probably not feed from the magazine of most purpose built .308 length actions or military detachable box magazines.
Some 7.62 sniper rifles are built on .30-06 length actions, but would need the throat deepened for over length loads.

Quote:
Both loads had peak pressures not to far from blue pill proof test loads; much higher than standard specs for the 7.62 NATO round.
Which was what I was getting at.
A load that beats a match rifle to death in a fraction of the normal useful life is not much of a bargin unless Uncle Sugar is paying the bills.
Then again many match shooters of the thirties and earlier used hi nitro powders that destroyed the accuracy of expensive matchgrade barrels within 300 rounds, but they were willing to pay the price for a very slight edge in accuracy.

I suspect that any noticable accuracy advantage of .308 match rifles was due more to lack of interest in keeping the .30-06 competitive. The new kid on the block was getting all the development funding.
Improved low nitro double base powders may have been part of it. The .30-06 having performed better with single base powders during WW2 and before.
Double base powders tested in 06 matchgrade ammo had some of the best mean radius figures yet the next lot would have mean radius inferior to the single base powders. Single base was far more consistent from one lot to the next than available double base in those days.
Throat erosion was still a problem with double base at the time, with ten percent shorter barrel life.
The garand also operated better with the gas port pressure of single base, and there was less erosion of gas ports.
The .308 was developed from ground up to accomodate double base powders, and the M-14 was designed to handle the hotter DB ball powders by use of chrome lined bores and high temperature resistent alloy in the gas system.

The .308 with its smaller capacity would have an advantage if kept within its normal performance range, just as specialized target rounds like the 8.15X46R or .32-40 had at closer ranges. Consistency within a certain envelope outweighing maximum performance figures.
The .308 is much like the .303 British in some respects, and a number of UK shooters have told of the most accurate .308 loads being basically a balistic duplicate of .303 matchgrade loads.

With maximum ranges of 1200 yards in recent matches some have found the hotter long range .308 loads to be too much for some older match rifles, especially the converted No.4 rifles.
A few more modern .308 match rifles have also been damaged by the top end loads needed to keep the bullet super sonic at 1200 yards to avoid transition shock.

I'm no barrel maker but seems to me that the 1:10 twist developed for the 1903 .30 and the .303 when both used bullets of 215-220 grains should still be best for bullets in this range or heavier.
They did not keep the 1:10 twist because of any expectation that it would be optimal for the 150 gr .30 or the 174 gr .303, though the lightweight nose plug of the MkVII bullet meant the length was practically the same as that of the 225 gr Swift matchgrade bullet and benefitted from the tighter twist.

A bullet of 200 gr or heavier being more accurate in a 1:11-1:12 twist barrel than in a 1:10 twist is counter intuitive.
There must be more to that story than twist alone.

Last edited by Rainbow Demon; November 22, 2012 at 03:18 AM.
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