Thread: .308 vs .30-06
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Old November 22, 2012, 08:54 AM   #66
Bart B.
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Join Date: February 15, 2009
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Would the (.308 Win.) long throat be due to seating the bullet far beyond the specified cartridge OAL?
Yes.

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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.
The first .308 bolt action rifle was built on a standard length action with a spacer at the back of it’s .30-06 length box magazine. But the first USA made military sniper rifle was made using the Rem. 700 short action; same one their commercial version used. Best shots in the Army and Marine Corps wanted the Win. 70 action to be used as it was more reliable, stiffer and easier to maintain in the field than the Rem. 700. But Winchester was in dire financial straits at the time and Uncle Sam didn’t want to take a chance with them.

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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.
Uncle Sugar spent zero dollars more maintaining M1 and M14NM rifles shooting those ultra hot loads. Properly built and op rods bent and fit to tight specs did not suffer. I’ve shot thousands of those loads and there were no problems.

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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.
Yes, and Hi Vel No. 2 was the favorite powder in the early 20th century and a good barrel for the M1903's from the DCM cost about $2.00. Those barrels lasted about 500 to 800 rounds of best accuracy.

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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.
There was no development funding. When the 26-year-old “new kid on the block” using one in match rifle competition in the 1963 Nationals chambered his Hart barrel with a standard SAAMI spec reamer, it tested to sub 4" groups at 600 yards using the same powder, bullets and bore/groove specs as the .30-06. He won the Nationals with it that year. The best .30-06 match rifles of the day shot about 6 inches at 600 yards with the best bullets available. A few years later when Sierra changed over to hollow point match bullets instead of FMJBT ones, the .308's accuracy dropped to 3" or better at 600 and the ‘06 to about 5" The .308's no better now with the best bullets available and that then-new kid’s still building them today.

The difference in accuracy was the specs for the leade angles; the .308's was less and distorted bullets less as they entered the rifling. Later tests with the .30-06 with leade’s having the same 1.5 degree leade angle proved there was not any significant difference in accuracy. But the longer barrel life and milder recoil of the .308 made it easier to shoot accuratly and at a lower cost.

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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 match grade 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.
I’m not aware of any double base (ball) powders being tried in 30 caliber M72 match ammo. Some Winchester ball powders were used in 7.62 NATO M118 match ammo in the late 1970's and its ho-hum accuracy of even the best lots were a disappointment to competitors.
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The garand also operated better with the gas port pressure of single base, and there was less erosion of gas ports.
Gas port erosion was never an issue with even service grade M1 or M14 rifles. The bore wore out for service accuracy standards at 8,000 to 10,000 rounds of both. Match grade barrels were typically replaced at 4000 to 5000 rounds.

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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.
Peak pressure specs for both 7.62 NATO and the 30 caliber M1 round were 50,000 CUP when the 7.62 NATO hit the street. Winchester chose to spec the .308's peak pressure at 52,000 CUP, same as their .270 Win. round, as it would be used in more modern rifles like the .270 was; and SAAMI bought the idea.

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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.
There was (and still is) no difference in accuracy with the .308 with reduced loads compared to full power ones. The 300 metre international free rifle folks liked mild loads for their .308's as the milder recoil made them easier to shoot accurate. Full power loads in NRA match rifles bested out at 300 yards with equal accuracy of about 1/3 MOA in the best of them. Nothing to date's equalled what a .308 did in 1971 shooting sub 1.5 inch 10-shot groups at 600 yards.

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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.
Note that the Brits use a different set of objectives in their fullbore long range matches. They’ve always insisted on leveling the playing (shooting?) field by making everyone shoot the same ammo. Arsenal ammo was used and still is. Handloads are not allowed. Good lots from Great Britian’s Radway Green Arsenal shot very well even with huge muzzle velocity spreads due to compensation of the SMLE’s barrel whip making long range accuracy much better than a Mauser action based rifle.

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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.
Which is why George Swenson, a British gunsmith, designed and made the Swing 4-lug single shot action in 1972. The British 7.62 NATO loads had a lower muzzle velocity spread and their SMLE’s rebarreled for that round didn’t shoot it all that accurate. That Swing action was the forerunner of more modern Paramount, RPA, Barnard, Musgrave and other single shot .308 Win. actions used in the Commonwealth’s fullbore matches. They kicked the pants off the USA 2-lug Winchester and Remington actions for accuracy with new cases from anywhere.

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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 match grade 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.
There is more. It’s the speed they leave the barrel at. Muzzle velocity and twist rate determine the rpm’s a bullet spins at. A given bullet weight and shape for a given caliber needs to be spun in a narrow velocity range to stabilize it well throughout its flight. Ballistic engineers at Frankfort Arsenal developing the 7.62 NATO round and the same folks at Winchester developing their .308 round knew the 150-gr. ball bullet from the .30-06 was spun too fast going out the barrel for best accuracy through 1000 yards. Harry Pope (famed barrel maker of the early 20th century) also knew a 1:10 twist was too fast for in the .30-06 Palma rifle barrels shooting 150-gr. bullets he made for the US Palma Team around 1920. They all used 1:12 twists for those barrels.

The Brits used 1:13 and 1:14 twist barrels in their fullbore long range match rifle 30 inch barrels shooting arsenal ammo’s 147-gr. FMJBT bullets. Bullets left at 2900 + fps and remained supersonic through 1000 yards. That slower rpm rate didn’t cause accuracy problems with bullets a bit unbalanced which is common in arsenal ammo. Spinning bullets too fast makes those even with a slight unbalance jump off the muzzle axis as the exit the barrel. Even today, benchresters adjust their charge weights for shorter ranges to make muzzle velocity just fast enough for the atmospehric conditions to stablize them for best accuracy at the lowest rpm rate that works. Best example's the .30BR shooting 115 to 135 grain bullets out around 3000 fps from 1:15 to 1:18 twist barrels.

Last edited by Bart B.; November 22, 2012 at 10:33 AM.
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