M41 .38 Special Ballistics


#1

Several weeks ago I got a full box of U. S. Military M41 .38 Special FMJ, HS WCC 68. Official government performance specs for this round are given as:
Velocity = 950 +/- 45 ft/sec @ 15 ft; SD <= 27 ft/sec (test barrel particulars not provided)

I was doing some .38 Special load development today, and decided to find what the actual measured velocity of the M41 was using my chronograph (also at 15’ from the muzzle). I fired 5 rounds of M41 in each of two target revolvers, each having a 6" barrel. My results follow.

Revolver 1 (S&W)- Average MV= 777.4 ft/sec; SD= 25.2 ft/sec; Variance= 8.6% (Vmax-Vmin)/Vavg
Revolver 2 (Colt) - Average MV= 867.2 ft/sec; SD= 22.2 ft/sec; Variance= 7.2%

I find it unusual that both my average velocity measurements were significantly below the given minimum specification (905 ft/sec). While the specs don’t state a test barrel length, U. S. military .38 Special revolvers typically have (had) 4" barrels. Therefore I would also expect my 6" barrels to give even greater velocity. Temperature would not be an answer, as it was in the mid-60s all afternoon. Perhaps the M41 lot acceptance test is performed from a vented barrel of greater length, and does not use a revolver at all. That would not be unusual, as the LAT of the U. S. military 9mm M882 ball uses, I think, an approximate 8" test barrel, not the 5" barrel of the M9 pistol.

Differences in average MV between the two revolvers is not unusual, but not to that extent (90 ft/sec). Generally, differences have been no more than 30 to 50 ft/sec for other loads.

Any other ideas about the M41 velocity differences? Does anyone have the MILSPEC test procedure for the M41?


#2

I am not surprised to see that the Colt achieved higher velocity than the Smith and Wesson with this FMJ ammo. I don’t know the bullet diameter the government used, but my Colt Python barrel (6") is about 9 mm (roughly .356") and my Smith and Wesson Model 28 (4") is about .358".

My Python is, by far, the more accurate of the two pistols when fired with match grade Winchester 148 grain wadcutter, the only load I ever had test in Ransom Rests with the two revolvers. That was a lot of years ago.

The Govt. Specs may show those higher velocities due to the use of a firing fixture rather than actual revolvers. I simply don’t know what type of equipment they used for testing, but I can’t think of anything else to explain the big difference. I am told that test fixtures generally yield higher than “real life” velocities, but I am a bit out of my knowledge level here.


#3

The gap between the cylinder and the forcing cone is responsible for roughly
100-150 fps decrease in velocity.

As you mentioned, velocity specs almost always come from test barrels, which
accounts for the difference.

It doesn’t inspire a lot of confidence in terms of ballistics, especially since most revolvers used for defense have 2 or 4 inch barrels.

It would be interesting to see the velocities from the same lot of M41 shot out of 4" and 2" inch barreled revolvers.

Nice work, BTW


#4

The old unvented SAAMI test barrel for .38 Special was 7.71 in long. Very probably this was used for military acceptance, too.

Edit: 5 shots is a very small number. In acceptance 20 were used.
The difference between your two revolvers is greater than one would normally expect.


#5

Actually, using an average velocity from five shots is not so bad. The average velocity of 5 shots vs. the average velocity of 20 shots from the same random universe at this level of sample SD will vary no more than about 2% in either direction.

I also thought the 90 ft/second MV difference between the two revolvers was unusually excessive. I usually test velocities of individual loads using both revolvers, and the difference in 5-shot MV averages generally will not exceed about 50 ft/sec, mostly somewhat less. But almost all of my testing involves lead bullets, not FMJs. That may have something to do with it, possibly involving greater bore friction.


#6

There are so many variables it would be futile to dwell on them all. Revolvers are as individual as people. However one spanner I will throw into the mix just in the hope of promoting a bit of interesting discussion and maybe drawing a few opinions.

The traditional powder, virtually universal, for .38 Spec was the one that starts with B. It was (then) just about the fastest burning powder on the market. In a 6" barrel the entire combustion would have taken place way before the bullet was even half way down the barrel and in the second half the bullet would have been slowing again due to friction.

The point I am making is that long barrel falloff is a known phenomonon which is why powders like the one beginning with a U take over for consistancy.

Pythons were always notoriously tight barrelled and so are a lot of modern Smiths. Jacketed bullets heat barrels a lot more than lead (all other things being the same) and I take that to indicate increased friction

Try it again in an ex mil mod 10 with a 4" barrel and a good old.360 barrel and see what you get then


#7

The original spec for 38 Special cartridges was 850 fps. Maybe you got some older stuff? Not very likely for 1968 ammo, but it’s a possibility.

AFAIK, M41 was never loaded with B or U. It was always a non-cannister DuPont or Hercules powder. I think the later ammunition was straight commercial, loaded with whatever Remchester was using at the time.

JMHO

Ray


#8

The M41 velocity spec I presented earlier came directly from the Lake City AAP Product Guide, even though the M41 was not manufactured there. But the PGU-12/B .38 Special round for the USAF was. Its velocity spec was 1100 to 1175 ft/sec @27 feet, in the same range as the .38/44. Propellant used for the PGU-12/B was HPC 23.

The guide gives the M41 propellant as being either SR 7325 or HPC 1. I do not know the commercial canister equivalent of those, but would expect they are something similar to powder U.

There is also an XM142 .38 Special round given. It appears to be the ballistic equivalent to the M41, but the propellant charges of the same propellants used for the M41 are slightly greater for the XM142 but the bullet is the same. Otherwise, I don’t see much difference between it and the M41 round. Maybe someone knows.


#9

Interesting information, gentlemen. Can you tell me the bullet weight of the PGU-12/B? What was that gun/ammo combination issued for?

I’d also be interested in some idea of the service dates for the M41 and PGU-12/B, if anyone knows them.


#10

M41 is covered by Specification MIL-C-46409D as of 1991.
Data is identical to the values mentioned in the first entry in this thread by DennisK.

The .38 Special reference cartridge for use with M41 is covered by MIL-C-46392 of November 1963.
Velocity is the same as for M41, but pressure 16000 psi.

PGU-12/B is covered by MIL-C-48551 of June 1975, last amended in 1991.
(All three specifications were downloadable from DTIC, probably still are. The ASSIST Database was unavailable when I checked recently.)
Velocity is given as 1125 fps. Pressure is 20000 psi, compared to 17000 for M41.

DARCOM Pamphlet AMC-P 700-3-2 of May 1984 gives the bullet weight of M41 as 132.0-3.5 grains. Ruger SS84-L is mentioned as a weapon (SS is Security Six or Service Six, I assume.) apart from unspecified 2" und 4" revolver.

My notes, which alas are from the time when I did not keep track of sources, say PGU-12/B has the same bullet weight as M41: 130gr. The other data in my notes are identical to the values given above. Considering the velocity and the pressure, it seems highly probable to me that M41 and PGU-12/B use the same bullet weight.


#11

Many thanks!


#12

Regarding the PGU-12/B, the story is that USAF security personnel (who used the S&W K-38 Combat Masterpiece, Model 15 at the time), felt the M41 round was too anemic. Some users took the do-it-yourself approach by pulling pullets and doubling the powder charge. Apparently, the M41 bullet pull wasn’t much and the bullets could be easily pulled. Of course, this resulted in incidents of blown-up revolvers. I have had several former USAF security cops tell me this story, and I believe it is factual. To prevent this, someone with enough influence decreed that USAF would change to a more powerful .38 Special round with a much higher bullet pull. This was the PGU-12/B. 72 million rounds were made at Lake City for the USAF in 1979-80, the only time Lake City made .38 Special ammunition.

Specifications for the PGU-12/B were originally in MIL-C-48551 as earlier stated. Other information is below.

Velocity: 1125 ft/sec +50-25 @27’ (i.e., 1100-1175 ft/sec)
Chamber Pressure: Average <=20,000 psi, 24,000 psi individual maximum
Grouping Performance: 7.46" diagonal @50 yards (number of shots unstated)
Bullet Pull: 130 pounds minimum (bullet was very heavily crimped)
Bullet: Jacketed lead core, 132-3.5 grains (jacket CA220, 90/10)
Cartridge weight: 204 grains COAL: 1.347"-0.020
Propellant: HPC 23 (I won’t give the charge)
Primer Mix: 5061W (see below)

5061W Primer Mix:
Lead Styphnate 38%
Barium Nitrate 43%
Strontium Sulfide 5 9%
Calcium Silicide 8%
Tetracene 2%


#13

I always thought the XM142 was 158 grain and the M41 was 130 grain. Are you saying they’re both 130 grain FMJ?

Also, Dennis, could you PM me the charge weight on the PGU-12/B if you don’t wish to post it? I would like to see if it matches what I have in my records.


#14

My mistake, was looking at the wrong page. The XM142 does have a 158 grain bullet. Bullet spec calls for 158 -3 grains, also jacketed.
SR 7325 or HPC 1 propellants. 925 +/- 25 Ft/Sec @15’, SD <=27, Chamber pressure <= 20,000 psi, accuracy <=2" MR @ 50 yords. Will provide charge weights by PM.


#15

Interesting thread. It got me looking through my 38 Special cartridges. Is there a good way of determining if a round is a M41, M41-E2, XM 142, PGU -12/B, or a T276 ?
It would appear the M41- E2 is about 2.5mm shorter. Brandt lists it as experimental and it looks from the drawing to be similar to the AMU round. The T276 is listed in COW 6th edition chapter15 but no description other than .38 special


#16

Re the M41-E2. I fount this in an old posting on the S&W Forum
"Introduced by the Army, the experimental M41E2 had a shorter case than the standard .38 Special (1.056 inch compared to 1.150 inch). The bullet was deeply seated with the case meeting the bullet’s ogive. This deep seating was done to reduce airspace in the case, and improve ignition. The American Rifleman notes that this cartridge is not commonly encountered. Velocity was the same as the M41: 720 to 770 fps."

Perhaps the MV given for the E2 was that from a 4" revolver barrel, not a LAT standard barrel. It makes one wonder why they bothered with doing any development. Why not just go back to the .38 Long Colt with a FMJ bullet if this is all the performance they wanted?

I will try to provide more detailed information about the M41, XM142, and PGU-12/B differences later this week after I get some other matters in order.


#17

From the specs and drawings I have, this is a dimensional and weight comparison of the PGU-12/B, M-41, and XM142 .38 Special cartridges.

Case: All three rounds use the same case specification, drawing 7553601, alloy CA260 (70/30), weight approx. 63.5 grains

COAL: PGU-12/B - 1.347"-0.020"; M41 and XM142 - 1.550"-0.020"

Bullet: PGU-12/B - Drawing 11735597 or 12902904 (alt), FMJ, length 0.593"-0.015", nose radius 0.137", weight 132-3.5 grains
M41 - Drawing 7553692 or 12902904 (alt), FMJ, length 0.593"-0.015", nose radius 0.137", weight 132-3.5 grains
(NOTE: drawings 11735597 and 7553692 appear to have essentially identical dimensioning. Alternate bullet drawing numbers are identical)
XM142 - Drawing 10520246, FMJ, length 0.690"-0.020", nose radius 0.137", weight 158-3 grains

Bullet jacket alloy is CA220 (90/10) for all bullet types. Length from bullet nose to top of cannelure ring is 0.360"+0.010" for PGU-12/B, variable to get correct COAL for M41, and 0.385-0.10" for XM142 bullets.

Loaded cartridge weights: PGU-12/B - 204 grains (approx.); M41 - 203 grains (approx.); XM142 - 229.3 +/- 5 grains

In summary, the PGU-12/B COAL is shorter and has a more deeply seated bullet than the M41 and XM142, while the XM142 cartridge’s weight is somewhat greater than the PGU-12/B and M41.


#18

Thank you
Any information on the T276 round


#19

I have no information about the T276. Maybe someone else does.