You can fireform that brass without seating a bullet. Maybe try that and see how the brass mate with dies. Here's a link.
Well, crap. The forum doesn't allow a link. Maybe I can cut and paste the post. Okay, here it is.
Fire Forming Improved Rifle Cases Without a Bullet
INTJ [posted by]
I have done this with three sets of brass now and this last time I tracked things more carefully. The old rule of thumb is to fill the case 2/3 full of pistol powder then use Cream of Wheat, oatmeal, wax, soap, etc. to keep the powder in place. Here is how I did it this last time. Use this method at your own risk, I assume no liability whatsoever.
I fire formed about 200 Lapua 6BR cases into 6 BR Ackley. This process moves the shoulder forward a little and changes the shoulder angle from 30 degrees to 40 degrees.
I used Fed 205 primers, 20 grains of Bullseye, and 1/8 piece of toilet paper. I neck-turned these cases and cut a little into the shoulder. When I chambered the barrel I made sure that the bolt would just close on a 6 BRA go gauge.
After firing with the Bullseye and TP, the shoulders measured 1.148"-1.150" on my Mitutoyo calipers with a Whidden insert. Most were 1.1495", if I can reliably measure to .0005" with that setup (questionable). The shoulder diameter measured .463 and the base diameter measured .4685. After subsequently shooting those fire formed cases with a bullet during load development, the shoulder length was 1.149, shoulder diameter .463 and base diameter .470. I consider that close enough to begin load development. My die sizes the base back to .4685 and the shoulder is wherever I want it.
While I did not have to shoot any bullets through the bore during fire forming I knew there would still be carbon to clean out. I thought there would be a lot but when I looked with the Hawkeye borescope all I saw was a very light gray coating that cleaned up fairly easily. There was no throat erosion or fire cracking.
So far load development with this barrel is going okay, about like when I fire form with bullets.
A couple of notes.
You must use a softer primer for best results. From previous experience I know that a CCI BR4 will not reliably fire with a case neck-turned into the shoulder. The Fed 205s worked great.
The barrel gets very hot if you crank through 200 all at once. I put wet rags the length of the barrel and would shoot 50 in a row, then re-wet the rags. That was on a 40 degree day. In the heat of the summer you would have to go slower.
20 grains of Bullseye very noticeably shoots flame out of a 29.5" barrel. I don't know if I would want to try this with my 300 Ackley with 50 grains of Bullseye, but in theory it would work. Then again, with a hunting rifle I wouldn't need 200 cases--50 would be enough so I'd probably just use bullets.
If you think you need 200 rounds down your barrel before it's even worth trying to tune a load, then this method is of no value--you might as well fire form with bullets. If you think the barrel shoots it's best when its at its freshest and don't have a fire forming barrel, this method works well.
It's not any faster to stuff the toilet paper into the neck than it is to load a bullet, and you might want to wait until the toilet paper supply chain catches back up before using this method...........
Use this method at your own risk, I assume no liability whatsoever.
