Mine was a 375 H&H that I had rebarreled to 500 NE 3 1/4" and it's a lot of fun. 50 caliber is cheaper to shoot than 577, and the only machining that was done was opening the loading trough a bit and taking a bit off the top of the block. No safety modifications were needed. It has a Douglas barrel with custom quarter rib with a standing express sight and machined for Talley QD rings.