My preferred method is cast the chamber in cerrosafe and knock casting with separated brass out, I have done it with a dental pick dug into the side of the soft brass casing, THIS IS INSIDE THE CASING, then pull back if it comes loose it just needs to move a fraction of inch. Not much of a shoulder on that 375 to headspace off of, original purpose of the H&H belt was supply a good stop to set headspace, if you handload you can seat the bullet out long to engage rifling, then neck size and make your brass last many firings without any separations, your Ruger No1 is perfect for this set up. Seating the bullet this way may increase pressure some, so start low and work up is always good advice and never exceeding published maximum data is good advice too!