I slugged the bore of mine, first with a .535" round ball, as near as I can tell, groove depth is ~.510"ish, real hard to measure tho, I wrapped a .0025" feeler gauge blade around it to get a measurement of .515" then subtracted .005" for .510". I also drove a .510" 300gr Barnes into the muzzle part way in, the bullet actually measures .509", the grooves left marks between most of the lands meaning the bullet wasn't quite square in the muzzle probably or the one groove was slightly deeper than the others. I'll get the .515" cast bullets tomorrow and let ya know if they'll chamber.
As for shooting .515" jacketed bullets in a .512" barrel, as long as they'll chamber, they should work fine, I've shot .2835"(7mm) bullet in my overbore 270 Ackley Handi which slugs .2795" in the groove, just have to work the load up to deal with the increased pressure of the slightly larger bullet. Remember the member here that had his 243 Handi at the range and his friend loaded it with a 7.62x39 round accidently and fired it? It fired with no catastrophic failure, just created a lot of pressure, but the bullet went down the bore, it did lock it up so they couldn't open the action which wasn't damaged after H&R inspected it, underlug was toast tho, they replaced the barrel at the owner's cost and returned it to him.
Tim
