Practical Dope on the Big Bores
F.C. Ness
Chapter 11
7 MM. Factory Loads
The Military .276 Pedersen
The .276 Pedersen cartridge, once made by the Frankford Arsenal for the Pedersen and Garand semi-automatic experimental military rifles in 7 mm. Caliber, was obsoleted by the order of General MacArthur while he was Chief of Staff.
The .276 Pedersen cartridge is loaded with a 125-grain F.M.J. pointed boat-tail bullet, and the average charge (by our own breakdown test and scales) is 31.7 grains weight of I.M.R. powder No. 25, Lot 1324, which gives the bullet an initial velocity of about 2700 f.s. In appearance (shape, color, and size of kernels) this powder lies between No. 4198 and Pyro D.G. I.M.R. No. 25 has never been made available as a canister powder, but it is very similar to I.M.R. No. 4198 which has supplanted it.
An idea of the physical characteristics of this .276 Pedersen cartridge may be had by studying the accompanying line cut. The bullet is .284 caliber; a true 7 mm. The .276 figure refers to the bore diameter. The lead-alloy core (seven parts lead and one part antimony) weighs 83 grains, while the gilding metal jacket brings the total to 126 grains. The pointed bullet has an ogive radius of 10 calibers. The W/d2 is .222. Its exterior ballistics approximate those of the M1 and M2 .30 caliber Service ammunition; its “C” value lies between the two.
According to our duPont ballistic charts the relative ballistic coefficient of the 172-grain M1 bullet is .560 and that of the 150-grain M2 bullet is .469, while that of the 125-grain .276 Pedersen is .515. Bear in mind these are relative values and arbitrary figures. This fine little 7 mm. Bullet is perfectly streamlined. Unlike the two .30 caliber Service bullets it has no cylindrical portion or parallel sides, but a continuous curve from its sharp point to the edge of its boat-tailed and concaved base. When forced into the rifling, however, it has a bearing-length of about 3/8 inch. Its total length, by our own measurement, is 1.214 inches. The standard twist of rifling for it was one turn in 9 inches. Standard 7 mm. Mauser barrels, according to origin, have rifling pitches of 1 to 8 and 1 to 10, making any of them suitable.
The trajectory of the .276 Pedersen bullets closely agrees with that of our M1 Service bullet up to 1000 yards, and its accuracy is fair, up to 600 yards at least. Because of its lighter weight the recoil is less; not half as much as that of the .30 caliber. Because the case head is smaller in area, the backthrust on the bolt is less. Because the powder load is 40 percent less and its chamber pressures are slightly lower, it develops less heat than the .30 caliber, or only about 40 per cent as much. That is, 200 rounds of .30 caliber ammunition will make the barrel just as hot as 500 rounds of .276 Pedersen ammunition under equal conditions of firing.
In overall length, the .276 Pedersen, rimless bottle-neck cartridge is about ½-inch shorter than the .30-’06, and the mouth of its case comes only up to the .30-’06 shoulder when the two are set side-by-side on their bases. Whereas head diameter and the base of the .30-’06 is .471 inch the .276 case measures .446 inch at these same points. The body of the case has appreciably more taper than that of the .30-’06. The 6 mm. Lee-Navy and 6.5 mm. Mannlicher have very nearly the base diameter of the .276 Pedersen. They are only slightly smaller, while the .25, .30, and .32 Remington rimless bases are considerably smaller, or .418-inch in diameter. Because of this discrepancy, bolt faces made for these other standard cartridges may have to be weld-filled and reshaped to fit the .276 Pedersen case head properly.
Only a couple-dozen semi-automatic rifles, more or less, were made for this cartridge, and these experimental military arms qualify best as museum pieces. Consequently, existing rifles had to be converted to take this .276 Pedersen cartridge. For this purpose, rifles in the 7 mm. Mauser caliber were best. Griffin & Howe, 202 E. 44th Street, New York City, made up chambering reamers. Prices, varied with the amount of work requires on the individual rifle. Vernor Gipson, Chicago, also prepared chambering reamers and gave estimates or quotations on such work. We have been informed that W. A. Sukalle, Phoenix, Arizona, made barrels and chambering reamers for this cartridge and completed one rifle for it.
Our first .276 Pedersen rifle was a cheap, short, light. Model 1893 Spanish Mauser carbine converted by Vernor Gipson. Its 23 ¼ -inch barrel was tapered, in three steps, to 5/8 at the muzzle from its 1 1/8-inch breech. The groove diameter was .284 inch and the pitch of rifling had one complete turn in nine inches.
The bore fouled quite badly, midway to the muzzle, but no bullet tipping resulted at any range up to 300 yards. Our lot No. 23 ammunition had large-size, .210-inch primers, while our lot No. 21 had the .175-inch, small size. No difference in performance was noted between these two. Our 100-yard groups ran: 2.63, 2.88, 5.63, 5.77, 4.24, 5.15, 2.65, 3.08, 3.60, 7.10, 6.00, 5.13, and 2.42 inches. At 200 yards we had about the same results, including groups of 5.85, 3.84, 4.45, 2.33, 2.65, 7.78, and 4.45 inches. At 300 yards, they were: 10.78, 3.75, and 16.0 inches.
Our final rifle was a 7 mm. Mauser Model 54 Winchester converted by Griffin & Howe. The same F.A. 1929 ammunition gave 100-yard groups of 5.08, 7.08, 4.48, 1.73, 5.20, 3.08, 3.77 inches. No uniformity!
Florich’s .276 Pedersen
“The writer was fortunate in getting a rifle in caliber .276 Pedersen. A new Target Model Win. M54 rifle in cal. 7 mm. was used. Griffin & Howe cut off the barrel breech sufficiently to permit rechambering it closely to .276 Pedersen:
“Firing the rifle with Lot 23 F.A. 1929 ammunition, using a Fecker 8X scope, much expectancy was rudely and speedily dispelled. At 100 yards the groups ran three inches or slightly more. Every detail that could be checked was checked. The chamber was close. The headspace tolerance was close to zero- it took a push downward to close the bolt- the throat was close for the 125-grain boat-tail bullet. The bore was a smooth, even .284 inch throughout. The rifle and scope were capable of minute of angle groups if the ammunition was right.
“A check of the Lot 23 cal. .276 ammunition showed about the same uniformity that good F.F. .30-’06 service loading would. For example, a breakdown of many rounds gave the following data:
Powder Bullet
Low 32.0 125.3
Average of 10 32.2 126.8
High 32.5 128.0
The bullets run .284 inch diameter very uniformly.
“A friend had a Springfield action rebarreled by Vernor Gipson. A new Remington barrel taken from a Remington rolling block 7 mm. single-shot military rifle was used. A similar rifle with regular commercial 7 mm. 175-grain soft-point ammunition had shot possibles at 100 yards on the small-bore target, with as-issued military sights, so much hope was placed in the .276 Pedersen on the Springfield action. Incidentally, the M54 action and the M1903 action handled the .276 Pedersen ammunition without any change being made in the magazine, bolt head, extractor, or ejector. Both rifles feed, fire, extract, and eject without any difficulty, cramping, or tendency to jam.
“On the range, the .276 Springfield with iron sights gave the same sort of groups; none under three inches at 100 yards, and the owner of the rifle sold it, disappointed, and gave the whole business up as a bad job. The writer still felt that the .276 Pedersen was capable of the kind of accuracy that cartridge would lead you to expect.
“Fired cases were decapped, the crimp primer pockets opened with a Schmitt tool, altered to .276 caliber, and made ready for reloading. The neck anneal on the Lot 23 cases seldom extends below the neck, and some unfired ammunition showed season cracks. Those bullets were pulled for future use and the powder saved.
“Study of the F.A. bullet leads the writer to believe that too much of the weight is to the rear, which could increase yaw and, on the target, yaw means large groups. To eliminate that possibility, some Western Tool and Copper Works, 7 mm. open-point, 123-grain, flat-base, bullets were loaded ahead of 32.0 grains of duPont No. 25 powder- the load as found in the F.A. Lot 23, ammunition- with the Remington 8 ½ primer. The cartridge length was 69 mm., which just enabled the bullet to touch the lead.
“On two different ranges, on two different days, some firing was done and Lot 23 F.A. gave groups of three minutes of angle for four riflemen, with the M54 and 8X glass. Finally, the handloads were tried. The first rifleman got 1 ¾-inch groups of ten rounds. Another put four into 1 ¼ inches and pulled his fifth shot to enlarge it to 1 7/8. The third got a group of under one inch for nine of ten shots, calling his fourth shot low and out of the group. It enlarged the group to 1 5/8 inches.
“So far as can be discovered, no one has reported groups like the above. Thos riflemen who could not make the .276 Pedersen group are urged to try bullets other than the F.A, make, in weights lighter than 130 grains, like the W.T. & C.W., or Barnes. The results will probably revive our interest in the .276 Pedersen cartridge.” – Thomas C. Florich.
Note: My own Griffin & Howe Winchester 54 put eight shots of Florich’s load in 2.72 inches and five shots in 3.74 inches at 200 yards; also five shots in 2.27 inches at 100 yards. The best with the F.A. 1929 Pedersen load was eight in 2.92 inches at 100 yards. F. C. N.
The expected accuracy of the 7 mm. Mauser in Model 54 is 2.75-inch at 100 yards against 2.25 inch for the best .30-’06 loads in similar rifles.
The $400 Geo. Gibbs 7 mm. Mauser was guaranteed (in London) to give 2.0-inch groups at 200 yards.
From the drawing in the text:
OAL: 2.855"
Case: 2.023
Bullet: 1.208
Neck dia. .313
Rim: .450
Head: .450
Rim thickness: .055
Rim to Shoulder: 1.6469
Shoulder to case mouth: .362"
I hope this helps.
