Proof Pressure Question

[doverham]

I am trying to figure out what can be safely shot out of a between-the-wars German shotgun, and have not been able to answer the question using the Standard Directory of Proof Marks. The gun in question was proofed Nitro in Suhl in 1936 with 70mm chambers. Is there a way to determine the applicable proof or service pressures? If possible, I would like use "moderate" nontox waterfowl loads (eg, Hevishot 1 1/4 oz 1300fps loads in a 2 3/4" case - I understand that these shells run in the 9500 psi range).

I plan to have a competent gunsmith evaluate the gun as well but would like to do some research in advance.

Thanks in advance, Doverham

[mike ford]

Doverham,
You didn't say what ga. your gun is chambered for,but since it was proofed for 70mm chambers, it should be safe with with any modern shells loaded to accepted commercial standards. The gun may not be reccomended for steel shot due to the choke, but I don't know if "Hevishot" will hurt it or not. Recommend the manufacturer of the shells be consulted.
Mike

[doverham]

Thanks for the response, Mike - it is a 12 bore

[Büchsemann]

Doverham,

I second what Mike says about the use of modern 2 3/4" shot cartridges in your 70mm chambers as being "safe" in an early gun proofed "Nitro" but the use of non-toxic shot is another matter and for a different reason. How are your barrels choked? I'm not familiar with Hevishot but if its hardness is that of a softer lead alloy or Bismuth I image that you wouldn't run into any difficulties. I'm guessing that you already know this but steel shot or relatively hard shot can raise hell on early soldered tubes by popping the ribs lose. Hard shot passing through tight constriction (full chokes) has little place to go as there is less "give" in the shot material to absorb the shock when the shot hits the choke. The typically heavy plastic wad cups in non-toxic loads help some but then again many of the German guns are choked pretty tight. Now if you're like Doug Kellermann and typically open up your chokes I doubt that you would have any problems in this regard.

Büchsemann

[doverham]

Büchsemann - thanks, I was aware of the issues with steel but have discovered that Hevishot is just as hard as steel. This gun is choked full/full, so clearly steel or Hevishot would not work through those chokes, aside from any potential pressure issues. It looks like Kent Tungsten Matrix Impact shot is softer and would avoid that problem. They offer a 1 1/4 oz/1400 fps load - I have asked them for pressure data but have not heard back yet.

Kent claims that their TM load is "Safe in old English Guns". Since we all know German guns are more stout than Brit guns, I should be all set!

[doverham]

I just received the following pressure information from Kent"

The 1 3/8 oz. 12 gauge 2 3/4" load has a pressure of 11,400
The 1 1/4 oz. 12 gauge 2 3/4" load has a pressure of 9,900

This is an article by Tom Armbrust discussing Kent TM loads. The discussion can be a little hard to follow at times but he concludes that Kent TM shot produces about 10% higher pressures than typical lead shot (all other load variables being equal).

http://www.armbrust.acf2.org/tungmatrix.htm

[Büchsemann]

Doverham,

This in particular caught my eye and all-in-all the stuff sounds pretty good:

"Another great feature of Tungsten Matrix shot is its complete safe usage in fine old double barreled shotguns, such as Parkers, Fox, L.C. Smith, and Winchester 21's, plus Browning Auto-5's and Winchester M-12 guns and also fine English double shotguns. Thin barrel walls and tight chokes pose no problems with this new shot as it is malleable like lead."

Büchsemann