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?