So what you're saying is size so the neck/shoulder junction is a crush fit. Do I lube the casing this way? I just received my Gunwerks 300 win mag brass for testing. I wanna get a system before I try that and ruin good casings.
I'll probably just load bullets. I have lots of cheap bullets but no pistol powder and cream of wheat.
Yes. The resized 300WM brass shoulder should be set back such that prior to fire forming (whether with a seated bullet, or fireforming with the COW), the casing shoulder is in form contact with the chamber shoulder. At this point you should feel some obvious resistance when closing the bolt. No so much as the bolt lugs snag on the action. The bolt should start to close and some low level of force will be required to close the bolt.
You asked about lubing the exterior of the cases during the fire forming when shooting a bullet. The powder charge, and pressure, when fire forming with a bullet should be reduced well be low a maximum load. Like a starting load, or mid-way between starting and maximum. If you reduce your starting load by ~10% less than maximum load, you should be able to lightly lube the exterior of the casing, which will help the casing expand completely to the dimensions of the chamber.
I wouldn't lube the exterior of the casing on a maximum pressure load developed on cases without any case lube. The gun should hold together just fine, but you'll be placing extra force against the bolt lugs because the side walls of the casing won't grip the chamber and assist/resist case head setback forces.
I like, and prefer, COW fire forming. No wasted bullet, reduced throat erosion, less powder burned, less barrel heat, lower (but sudden) pressures. When I COW fire form, I use the slipperiest substance known to mankind (slight exaggeration), and lube the exterior of the case with it as the last step, just prior to chambering the casing and fire forming. I don't have to worry about bolt lug thrust fire forming with COW, even with the exterior of the casing lubricated with super duper lube. It's clear from looking at the primers after firing with Cream of Wheat that the chamber pressure is moderate at best.
Warning: So to be crystal clear, I don't lube bullet loaded cases that are even near full pressure loads firing a bullet down the bore. When I fire form with bullets, I reduce the powder charge about 10% for the initial fire forming. This entire thread described my Cream of Wheat (COW) fire forming technique. It only applies to fire forming cases using Cream of Wheat. That was my communication, or at least my intention.
