John Buhmiller was not only the source for the barrel of my wildcat .505 SRE, I spent a week with him and his wife at the Game COIN convention in San Antonio, TX in the spring of 1971, when I arranged for my first Safari with Ker, Downey & Selby. One of my heavy rifles had a muzzle brake made by John, which came with the barrel.

You might try to contact Jerry Fisher, stock maker extraordinary, who was a close friend of John's and would probably know about your rifle.