James White is a WWII Marine Veteran, NRA Instructor, Former ORA President, and Distinguished Marksman. He served the ORA for many years and began the Sharpshooter. This is from the Sharpshooter Archives, December 2002.
Ammunition used in NRA High Power Rifle matches is usually loaded with boat-tailed bullets. These bullets retain velocity better than flat-base bullets, have less wind deflection and are more accurate at longer ranges. They are also easier to seat into a cartridge case when loading. But these may not be the only advantages to be gained from boat-tailed bullets.
Some shooters have forgotten, and others might never have heard, that shooting boat-tailed bullets in .30 caliber rifle barrels has the effect of improving accuracy and prolonging accuracy life. The old saw goes that “everyone knows that boat-tailed and armor-piercing bullets are hard on barrels.” But, a body of evidence has been built up that tells a different story.
This phenomenon is of interest mainly to shooters of NRA match rifles. The total number of shots fired in the life of the average hunting rifle is usually far fewer than the shots fired in a match rifle in one shooting season, and, in most cases, the number of shots fired from the average hunting rifle in its lifetime is probably not enough for it to begin to reach its highest level of accuracy.
In 1945, Frankford Arsenal began test-firing .30 caliber ammunition loaded with AP M2 armor-piercing bullets. These bullets weighted about 168 grains, several grains less than boat-tailed 172 grain M1 Ball bullets (not to be confused with the M1 Rifle). Several months of plotting group sizes versus shots fired showed a definite pattern.
With a new barrel, accuracy improved quickly during the first 500 to 1,000 rounds, then, as expected, at a slower rate up to 2,000 to 3,000 rounds. The general consensus was that the barrels should then suffer a gradual deterioration of accuracy corresponding to the erosion of the throat. But this did not happen. Accuracy gradually improved for many thousands of rounds more. The test barrels were removed from service at about 8,000 rounds, but indications were that they could have fired up to 10,000 rounds with little loss of accuracy.
With flat-based 152 grain M2 Ball bullets there was no such accuracy improvement. Accuracy peak at about 2,000 rounds and started to drop off badly several thousand rounds after that. (A friend of mine, while in the Marine Corps, shot in the Marine Corps Matches which were held at Quantico, Virginia, in 1946. The ammunition used during the matches was an accurate lot of .30 caliber AP M2).
In 1956, Frankford Arsenal began to develop match ammunition. The boat-tailed 172 grain match bullet, similar to the boat-tailed M1 Ball bullet, gave the same effect demonstrated by the AP M2. Accuracy improved rapidly for the first several hundred rounds, more slowly for the next 2,000 to 3,000 rounds, with a gradual accuracy improvement u to 8,000 to 10,000 rounds total.
This effect consistently occurred with each test barrel. Even though the test barrels were badly eroded in the throat area, the accuracy improvement continued. Barrels eroded for as much as 2 inches in front of the chamber and with severe guttering were at the peak of their shooting accuracy with AP M2 and M72 ammunition. This information is from February 1960 and September 1964 articles in The American Rifleman magazine.
Rounds fired in the test barrels were slow fire, although each 10-shot string was “pushed through at a fairly fast cadence.” But, with time out for target changes between 10-shot strings, barrels never became excessively hot. What might happen if a barrel had been frequently overheated by fas firing?
In 1985, a shooter on the All-National Guard Rifle Team, in the National Trophy Team Match at Camp Perry, Ohio, fired a score of 499 out of a possible 500 points. Of course, the “nine” that the shooter fired at 600 yards was “the coach’s fault.” The coach had been having the shooter tweak his sight to score a higher “X” count, and he miscalculated. Never mind that many of the ‘tens” that the shooter fired were probably due to the highly competent coaching he received from the same coach.
National Trophy matches shoot the 50-shot National Match course which is fired at 200, 300 and 600 yard distances. Forty percent of the shots fired are rapid fire. The m14 rifle the shooter used had also at one time been used for Infantry Trophy Match shooting.
The infantry Trophy match, or “Rattle Battle” as it is called, involves shooting as many rounds as can be fired while targets are exposed for 50 seconds at each of four distances. Hits count 4 points each at 600 yards, 3 points at 500 yards, 2 points at 300 yards, and 1 point at 200 yards. A six man team is allotted 384 rounds, or an average of 64 rounds per shooter. Shooters start in position, ready to fire when the targets appear. Most good teams have no rounds left after the 500 yard stage. Experienced Infantry Trophy shooters can get off almost 40 shots, including two magazine changes, during the 50 seconds that the target is exposed for firing.
The rifle fired by the All-National Guard shooter had seen some of this kind of service and had fired over 8,000 rounds through the same barrel at the time that it was used to shoot a score of 499 out of a possible 500 in the Ntional Trophy Team Match. The rifle had shot full power ammunition employing only military or commercial boat-tailed bullets in the 8,000 rounds. Sierra hollow point 168 grain boat-tailed bullets were arsenal loaded in the M852 National Match ammunition used to fire the high score.
Barrels whose accuracy is improved most by shooting boat-tailed bullets are probably those made of chrome-molybdenum steel. Many target barrels today are made of stainless steel, and some shoot tight groups form the first shot. Stainless steels used for barrel-making are softer than chrome-moly material but are more machinable and can be given a better internal finish.
A stainless steel barrel which has been lapped to a fine finish close to optimum size will probably not gain in accuracy from firing boat-tailed bullets; but continued firing of them might prolong the accuracy life of the barrel. A good chrome-moly barrel might never shoot groups as tight as a good stainless barrel, but will probably have a much longer accuracy life than the stainless barrel if boat-talied bullets are used exclusively.
A prominent maker of fine barrels for NRA Match rifles has found that, in his barrels, throat erosion will accelerate and the barrels will suddenly lose accuracy somewhere between 4,500 and 5,500 rounds. His barrels are made of a highly machineable re-sulpherized stainless steel which can be given an excellent internal finish. The accuracy life for his barrels is about twice the number of rounds observed by most bench-rest shooters, even though up to half the shots fired in NRA match rifles are rapid fire. Bullets used by most NRA match rifle shooters are of boat-tailed construction while bench-rest shooters usually shoot flat-based bullets.
The reason for the accuracy improvement effect from firing boat-tailed bullets is not known. One theory is that the shape of the boat-tail causes the diameter at the base of the bullet to tend to expand from the hammer blow of firing. Boat-tailed bullets smooth the bore by a burnishing action and tend to iron out tight spots. They tend to maintain length of bearing and conform better to eroded rifling.
Flat-based AP M2 bullets have a softer jacket material base over a hard steel core with a boat-tail shape. Apparently, the force of firing bushes the softer material onto the core and makes this base act inside the barrel as if it were boat-tailed. M80 bullets of 147 grain weight, loaded into 7.62 mm NATO ball ammunition are boat-tailed. These bullets, although launched with a slightly slower muzzle velocity, lose velocity at a slower rate and shoot better at longer ranges than flat-based 153 grain M2 Ball bullets in .30-06 ammunition. The M80 bullet, although six grains lighter and starting at a slower muzzle velocity, is actually traveling at a higher velocity than the M2 Ball bullet from about 300 yards on. It is not known if barrel accuracy life is extended by using M80 bullets.
Several other references to barrel life were found while doing research for this article. They may be of interest.
The earliest reference found, in a September 1969 American Rifleman article about ammunition for National Match competition, mentioned the effect of rapid fire with flat-base bullets. In 1906 the Krag-Jorgensen service rilfes issued to state teams had a barrel life of 1,200 to 3,500 rounds depending upon the amount of rapid fire. The .30-40 Krag ammunition was loaded with a flat-based 220 grain bullet.
Col. Towsend Whelen, in his April 1957 American Rifleman magazine article Only Accurate Rifles Are Interesting, told of weekly 500 yad bench-rest matches shot at the Walnut Hill, Massachusetts range in the early 1930’s. A man named Phillip Nutting was usually the winner. He shot a heavy barreled .30-06 Springfield. His hand-loaded ammunition, loaded with Frankford Arsenal 172 grain boat-tailed M1 bullets, usually shot groups of 5 to 7 inches – close to a minute of angle. After the rifle barrel had shot about 9,000 rounds, groups started to enlarge slightly. Bullets were then seated a little further out and accuracy was restored. The rifle continued to shoot well up to about 14000 rounds when Mr. Nutting died.
After a controversy, caused by the choice of the M1 Garand as the service rifle, a board of six Marine Corps officers began tests of various rifles in November 1940 (in April 1945 one of the board members, Col. Victor Bleasdale, was regimental commander of the 29th Marines of the Sixth Marine Division during the battle of Okinawa, for part of the time that the author of this article was a rifleman in that regiment). Forty enlisted Marines, with varying levels of shooting experience, did the firing. Four types of rifles were tested: two each of M1903, M1, Johnson, and Winchester rifles.
The M1903, M1 and Winchester rifles were either newly manufactured or had be re-barrelled and reconditioned before the tests. The two Johnson rifles were not new. prior to the tests one rifle had fired 10,000 rounds, the other 15,000 rounds.
Ammunition fired in the tests was from two lots of Palma Match ammunition: (FA Palma Match 1934 and FA Palma Match 1937) and one lot of M1 Ball; all loaded with 172 grain boat-tailed bullets. Palma was fired at long ranges, M1 Ball at short ranges.
The rifles were function fired, used and abused for about 9,000 rounds, then re-fired for accuracy at 200 yards. Accuracy wasn’t up to today’s standards but the two Johnson rifles compared favorably with the M1903 rifles and were slightly more accurate than the M1 rifles in this accuracy test, even though they had fired 19,000 and 24,000 rounds respectively prior to it. The tests were descibed in the book Book of the Garand by Major General Julian S. Hatcher.
A March 1956 American Rifleman article describes the expierneces of a Finnish gentleman named P.H. Naathanen. Over a 14-day period he fired, in a fixture, a rifle chambered for the 7.62 Russian cartridge whose case capacity is similar to that of the .308 Winchester. Boat-tailed bullets of 200 grain weight were used. Accuracy improved slowly through 14,000 rounds, at which point 300 meter, 10-shot groups shot into less than 2 -1/2 inch average diameter. The average group size then slowly increased, but at 17,000 rounds was still smaller than when the barrel was new. Firing continued until about 23,000 rounds. Group sizes at 300 meters averaged about 6-1/2 inches for 10 shots at the completion of firing.
To the average person, making a fast and shallow analysis of the shape of bullet bases, it just “stands to reason” the boat-tailed bullet bases would tend to “focus” the hot gases so that there would be a faster erosion rate when compared to flat-based bullets. But, in the world of the microscopically small gas molecule, the radius on the base of the bullet is no different than the angled base of the boat-tailed bullet. The gas pushes in all directions. There is no focusing of heat or pressure.
For whatever reason and by whatever mechanism, boat-tailed bullets, in actual practice, apparently do extend the accuracy life of a rifle barrel.
