I have had a 450 Alaskan in the Browning. The bbl threads
are different, and the original 348 chamber is tighter
than the Winchester. Its a good idea to study a fireformed case. That is where you start with a new wildcat rifle.

Brass brush & clean the chamber thoroughly-then fireform.
RCBS makes some really good form dies for the 450. Currently, I have two 450s on early Model 71 Winchesters that I have had for 20 years. They work very reliably.

If you plan to carry it hunting moose or bears, make sure it feeds and chambers consistently. You may also want to
experiment with various 458 bullets for accuracy and reliability. Good luck.

"The credit belongs to the man who is actually in the arena-not the critic"-T. Roosevelt
There are no atheists in fox holes or in the open doors of a para's aircraft.....