Was hoping someone smarter would help Jeremy. I assume you are planning on proof testing in the U.S.?

H.P. White Laboratory, Inc. in Maryland and Cortland, New York will proof to a pressure of 20,000 psi. A minimum pressure test would be 1 and 1/2 times the pressure of your intended load. www.hpwhite.com

Other options, and please let us know who you use and how it goes.

Chesapeake Testing
http://chesapeaketesting.com/services/outdoor-blast-testing/

Dayton T. Brown
http://www.dtbtest.com/Default.aspx

Re: Vintage 12g Black Powder Pressures
1 1/8 oz. 3 Drams (1200 fps) of DuPont FFFg (82 grains) is about 5000 psi.
1 1/8 oz. 3 Drams Curtis & Harvey’s No. 4, T.S. (82 grains; somewhat similar but not equivalent to medium grain FFg) was about 6500 psi.
1 1/4 oz. 3 1/4 Drams Curtis & Harvey’s No. 4, T.S. was about 8500 psi.

Black Powder substitute pressures from the 2001 “Lyman Black Powder Handbook & Loading Manual”
1 1/8 oz. with 100 gr. GOEX FFg at 1200 fps = 4,800 psi
1 1/8 oz. with 100 gr. Pyrodex RS at 1200 fps = 5,600 psi

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