Caprivi:
I just posted a shooting session with my 12.7x44 x 16ga last week. Fung gun to shoot.
I use brass from Buffalo arms made for the caliber. It is very close to the 50/70, but the smaller in diameter. The brass i have was made from .348 win brass. I had a few cases sent to me from buffalo that were made from 8mm Label. These were too small in the base after measuring. I sent them back and they replaced them, plus 4 more. I also have some betrem brass, but haven't tried them yet.

A message about loading. I used 777 power in mine. Afte the last shooting session, I noticed I had a little trouble opening the gun on one shot. I examined the primers and found they were pushing into the firing pin hole. Scared me. I looked at previous loading and the primers were not deformed like this.
I took the rest of the loaded cases and pullet the bullets and found that I had over compressed, somehow, the power. In some cases it was a solid mass.
The warnings from Hogdens is to NOT compress. I believe I spiked pressure with the compression. I must have miss judged the powder and seating depth.
I am backing away from the 777 until I figure out what happened. I will likely switch to black or 4198 loads.

This is a great gun to shoot and handle. I have an HVA M 17B SXS hammer gun.