Good Day,

Recently acquired a drilling I am having problems identifying the rifle caliber.
It is an Austrian Drilling marked Johann Perterlongo on one shotgun barrel and Tiroler Waffenfabrik on the other. It has the following letters under Crowns in various areas on the barrels S, U, W, G, N There is also 0/55g G.B.P over a line and under the line is STMG. The shotgun barrels have a 16 in a circle and 16/1, they are both also stamped Nitro. The shotguns chambers are definately 2.5" (65mm) and choked Full and Full+. It is an internal hammer gun, dual triggers and the front trigger is a set trigger.

The gentleman I got it from has been shooting the gun with modified 32-20 & 25-20 rounds. They are necked down to 25 Caliber (6.5mm) using a 25-20 die. I slugged the bore and it is fact a .257" groove diameter. He has also used 25-20 shells as well. When first fired it moves the shoulder ahead on the 25-20 rounds to fire form the brass.

I did a chamber cast and it appears the dimensions are as follows:
Rim: .425
Case diameter right above the rim: .348
From base to the shoulder: 1.058
Diamerter at the shoulder: .348
The neck above the shoulder is .300 and tapers to .282 and is about .350 long.
Overall Cartridge length is about 1.46 inch

I realize the 25-20 and the 32-20 cases are about .25" short but they seem to work fine and I am getting decent groups using a 75 grain Hornady Jacketed bullet with 7 - 7.5 grains of Alliant 2400 powder.

With taper of the neck I am thinking this may be a long throat but it is hard to tell. I have pored over all my cartrige of the World books and Donnelly's cartridge conversion book for obsolete cartridges and nothing.

Any thoughts on what it might be and the best parent brass and dies to use. Like I said it is shooting OK with what I am using so far just thought I would see if anyone had any thoughts on what it is??

Thanks in advance for any help you can render..

Sincerely,
DonT