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Bullet Speeds vs. Powder Location in Case



Load tests for .45 Colt:
(See note on Powders below or read all about various Powders.)

In extensive test with .45 Colt, I was getting spreads as great as 125 fps between shots. Trying to locate the reason for the variation, I shot a set of 6 shots carefully tapping the gun with muzzle in the air, and gently lowering the gun to level and firing off the shots. Then, I did the exact opposite, pointing the gun to the ground, tapping chamber, and raising to level to take the shots. Here are the surprising results.

Using 10 grains* of Unique (7 1/2" bbl)(only in Ruger and T/C) with a 250 grain RNFP lead bullet, pointing in the air to put powder rearward next to the primer, I got 1024 fps. The spread between the shots was 47 fps. Then shooting a set pointing to the ground between each shot, I got 848 fps. The spread between shots was 78 fps. The average difference between strings from powder in rear of case and powder in front of case was 176 fps.

Using 10 grains* of Unique (7 1/2" bbl)(only in Ruger and T/C) with a 255 grain SWC lead bullet, pointing in the air to put powder rearward next to the primer, I got 1007 fps. The spread between the shots was 34 fps. Then shooting a set pointing to the ground between each shot, I got 864 fps. The spread between shots was 70 fps. The average difference between strings from powder in rear of case and powder in front of case was 143 fps.

MASTER Commercial Ammo using 260 grain Jacketed Hollow Point bullet (powder unknown)(7 1/2" bbl) exhibited this performance:
Pointing in the air to put powder rearward next to the primer, I got 857 fps. The spread between the shots was 29 fps. Then shooting a set pointing to the ground between each shot, I got 742 fps. The spread between shots was 64 fps. The average difference between strings from powder in rear of case and powder in front of case was 115 fps.

Using 10 grains* of Unique (4 5/8" bbl)(only in Ruger and T/C) with a 250 grain Rainier FP bullet, pointing in the air to put powder rearward next to the primer, I got 981 fps. The spread between the shots was 40 fps. Then shooting a set pointing to the ground between each shot, I got 770 fps. The spread between shots was 118 fps. The average difference between strings from powder in rear of case and powder in front of case was 211 fps.

I believe some valid conclusions can be made here. If you point your gun skyward between shots, you will get higher velocities and a more consistent spread of speeds. Pointing the gun down and allowing powder to rest away from the primer and more next to the bullet, causes lower velocities and greater spread of speeds.
This would speak to using a powder that more nearly fills the case to minimize differences in powder position in a large case like the .45 colt. Certainly a load that was nearly a compressed load or a slightly compressed load, should be the most consistent you could shoot. I intend to further investigate this issue and find powders that have greater volumn to see how much this problem can be minimized. [6/23/96]

[7/20/96]

-----------------------------------------
230 grain Round Nose LEAD
    (Experiment with A5744 powder)
    AA5744     17.0 gr.     836 fps (powder pointing UP)
      (Hi=877.7  Lo=803.0  Spread=74.7 fps)

    AA5744     17.0 gr.     771 fps (powder pointing DOWN)
      (Hi=783.1  Lo=760.3  Spread=22.8 fps) 
-----------------------------------------
250 grain LRNFP  (Lead Round Nose, flat point)
    AA5744    17.0 gr.     853 (Powder UP - see note)
      (Hi=872.5  Lo=827.5  Spread=45 fps)
    AA5744    17.0 gr.     802 (Powder DOWN - see note)
      (Hi=809.2  Lo=792.6  Spread=16.6 fps)   
-----------------------------------------
Accurate Arms powder #5744 is a much more "case position insensitive" powder than others I have tried. I also used No. 9 which is slower and takes about 15 grains for a good Colt load, and it still showed about the same problems with case position, but not to quite the same extent as the faster powders. As of this time, this seems to be the best I have found. I plan to try others in this test. [7/20/96]

* This EXCEEDS the MAXIMUM load for Colt .45 for old and/or standard guns. Use ONLY in Ruger and T/C and modern rifles.

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This page created 6/23/96 by M.D. Smith and last modified on August 1, 1997 ©