Ok, so here is my quick theory on the perfect neck tension for the best accuracy out of a bolt gun. This is just my conclusion that I have come to over a few years of many rounds down range. I want to have minimum neck tension which means to me .001 neck tension if possible.
Here are a couple examples of developing my rounds with that goal of .001 neck tension in mind.
308 using Lapua brass which has a neck wall thickness of .014 X 2 for each side = .028. Add .308 bullet diameter to the .028 which means that 0 neck tension would be a .336 outside loaded neck diameter. I'm using a .335 neck bushing in a Reading neck only die which means I'm resizing .001 more than the .336. This is how I claim a .001 neck tension. This is what is shooting .5 moa most of the time out of a shilen 10 twist barrel.
The same math works for my 260AI. Same neck thickness of .014 with Lapua brass even though it's been necked up from .243, reamed, and turned. Anyway ((.014 X 2) = .028) + .264 =.292. I’m using a .291 Reading neck bushing die which again is a .001 neck tension. This is currently producing under .5 moa 5 shot groups all day long out of a Krieger 8 twist 30 inch barrel.
I ordered .289 and .288 neck bushings for my 6.5 Grendel AR which showed up today. The idea is that I want more realistic neck tension for a gas fed semi-auto AR platform. I should be able to get .003 and .004 neck tension for these rounds using the same math above. My question would be what neck tension is necessary to be safe in an AR platform with rounds that are not crimped?
Here are a couple examples of developing my rounds with that goal of .001 neck tension in mind.
308 using Lapua brass which has a neck wall thickness of .014 X 2 for each side = .028. Add .308 bullet diameter to the .028 which means that 0 neck tension would be a .336 outside loaded neck diameter. I'm using a .335 neck bushing in a Reading neck only die which means I'm resizing .001 more than the .336. This is how I claim a .001 neck tension. This is what is shooting .5 moa most of the time out of a shilen 10 twist barrel.
The same math works for my 260AI. Same neck thickness of .014 with Lapua brass even though it's been necked up from .243, reamed, and turned. Anyway ((.014 X 2) = .028) + .264 =.292. I’m using a .291 Reading neck bushing die which again is a .001 neck tension. This is currently producing under .5 moa 5 shot groups all day long out of a Krieger 8 twist 30 inch barrel.
I ordered .289 and .288 neck bushings for my 6.5 Grendel AR which showed up today. The idea is that I want more realistic neck tension for a gas fed semi-auto AR platform. I should be able to get .003 and .004 neck tension for these rounds using the same math above. My question would be what neck tension is necessary to be safe in an AR platform with rounds that are not crimped?