In my 38-55 target, I tried the fit on some 375 dia. bullets that I had for a 375 H&H. They would free drop thru the barrel from end to end. Didn't even touch the rifling enough to slow down on their way thru. You are most likely stuck with using .380 or .379 dia cast bullets in your rifle. Mine likes .380 dia cast flat points, 900-1100 fps. Good luck, and check jph45's posts on the subject. His and cheatermkII's adventures on reloading for this creature saved me an ulcer and a new bald spot. I was shooting good right off the bat. If you don't reload, you may be in for a struggle finding a consistent ammo supply. Hope this helps, Danny. PM if you want any details or sympathy.