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Re: Trapdoor receiver strength w/COW

Posted by Larry Gibson on Tuesday, 10 February 2009, at 10:39 a.m.


I recently conducted a pressure test of the 45-70 using 5744 for some fellows on another forum. The test was conducted using an Oehler M43 PBL. The rifle was a Siamese Mauser converted to 45-70 (no "strength" problems there). The load was 25 gr 5744 under a 413 gr commercial cast bullet. Test strings were 5 shots at 100yards. Results were;

25 gr 5744/no filler/2.1"/1166 fps/ 18,400 psi(M43) 25 gr 5744/3/4 gr dacron filler/1.45"/1226 fps/22,400 psi(M43) 25 gr 5744/2.5 gr dacron filler compressed/2.3"/1245 fps/22,300 psi(M43) 25 gr 5744/COW filler lightly compressed by bullet/5.6"/1294 fps/33,000 psi(M43)

Note the large pressure increase when the COW filler is used. Also the much worse accuracy. SAAMI MAP (Maximum Average Pressure) for TDs is 28,000 psi using piezo-electirc measurements and/strain gauges. That load at 33,000 psi was over pressure for the TD.

Limited tests with other powders including 4759 show similar increases in pressure when the COW filler is used. Accuracy sometimes is pretty good but pressures are over the top for TDs. I use the dacron filler at 1 1/4 gr with 5744, 4759 and 4895 with 400-420 gr cast bullets in my TDs with excellent accuracy at service rifle velocities of 1300-1350 fps. Ten shot groups at 100 yards run 2-2.5 MOA. In my H&R OM 36 gr 4895 under that same 413 gr cast bullet with the 1 1/4 gr dacron filler gives 1390 fps, 22,400 psi and the last 10 shot group at 100 yards was 2.3".

Larry Gibson


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