True confession here. I was the original purchaser of the GBO reamer for 454, I bought it to do the 3 rifles I had at the time. It was then donated to the site to help all you enablers out there to feed your own addictions. It is indeed a rifle reamer, with a smooth taper to the lands, not the abrupt shoulder for a forcing cone like the revolvers use. With my ancient vision, and a decent scope, it would originally do about a 2-3 inch group at 50 yds using 45 LC ammo. Factory or handloads made no difference much. After the reaming, it wil do a group just under half that. With my nephew the marine on board, she will shoot about a half inch, all with 45 LC. The Casull doesn't open it up much if any, or shoot any better either. I still have one, my grandson has one, one I traded for something else, but the results were the same for all of them. That was a long winded way of explaining that the reaming to 454 wont hurt LC accuracy at all, and probably will help.