Mine is .451 on the lands and .458 in the grooves also. This morning I tried to load some of those bullets I had cast with wheel weights andsized to .452. I figured I could force that .001 oversize into the bore, but could not do it. The bullet was just too hard. I could get it in a little over 2/3 its length, but no more - even banging on my very stout brass short starter with the heel of my hand. At least I had enough bullet sticking out that I could grab it with locking pliers and work it back out. It probably would have gone in with pure lead sized to .452, but .457 might be pretty tough, even with pure lead.