When the .458 Lott was first offered in CZ rifles. CZ simply reamed out the chamber and put a stamp on the barrel. Then reports came in about poor feeding. They did some experimenting and found out that there was merit to the claims of their Lott customers. The custom shop that makes these rifles for CZ found they had to play with the throat and rails. Significant machining was involved. They feed alright now, but many, many home 'smithed Lott rifles do not. Caveat emptor.