White .rifles made for big lead.my undestanding is 45 cal 1:20/ .50 cal 1:24. both designed for big lead conicals. after reading up on all of this stuff lol and seeing some of cayugads scary accurate results with a .451 white rifle and 488 gr conical.and the reviews on the no excuse web site and the results his customers get with the .45 cal whites and a 460 NE bullet. when i spoke to the gentleman from NE he told me the .45 cal rifles were getting better accuracy than the .50 cals. he shoots one himself.one thing i do know is the range of bullets with the 1:20 is very limited.no matter,what i really wanted to know originally are the GMB replacement .45 cal barrels 1:28 or 1:30,since reading the information on there site. i don't think they know lol.. Ray