I have piles of LC, BH, and Federal .308 brass. I hate to launch lapua .260 brass all over the country side with an ar10. I ran all three types of brass through a FL sizing die to turn them into .260 and I am getting about a .296 neck. My reamer is .297 neck (as are most). Has anyone made a fat neck reamer specifically designed to be used with no neck turn .308 brass like this? By the way, I refuse to turn necks especially for a gas gun where I'm going to loose it anyway. What would be the recommended neck thickness for a gas gun shooting this brass, .301 neck? What would happen if you shot normal .260 brass which has a much thinner neck through a chamber like this?
And if you're using a standard honed seating die, no you should be fine, my Redding Master Hunter die set (29531) has a competition seater with a spring and a micrometer on top, and my 2 dummy rounds were made from Federal .308 Win brass with both Nosler and Berger 6.5mm bullets, and they worked just fine in it... And the FL and Neck=sizer dies worked perfectly to size it down... However...Your's might be different and your neck-sizing and FL sizing dies, might not work. I have not tried to chamber them in my rifle, because I don't need to, I need the dummy rounds for quick setup with my micrometer seating die with different brands and weight bullets. It's a lot faster setup than mic'ing that shit out every single time and dialing it in for setup. Run the dummy, make your first REAL round, check it wit the calipers, if it's all good, start running them. I check each one regardless, but that's because I'm a bit anal-retentive about the level of precision that goes into my handloads. Even my plinking rounds. 
