Sorry, just saw your post.
I headspaced it using a 243AI Go-Gauge, it is a crush-fit for standard cases.
If hot is good for fireforming (and I've read you want to use full-power 243 loads) then I just made an couple of errors that created some VERY well fireformed cases.
First, I had been using IMR3031 and Nosler 55gr bullets to do some fireforming but I switched to RL17 and Barnes TTSX so I wanted to get the previous residue out of the barrel. I was short on time (how often does that lead to mistakes!) and I quickly cleaned the barrel and ran an oiled patch through it. I failed to use a bore mop to make sure the chamber was clean of oil.
I was working up the load using RL17 and Barnes TTSX bullets. I intended to have the bullets set .050 from the rifling. Somehow, I managed to set them 0.100 IN the rifling. I am surprised that I didn't noticed any additional force when closing the bolt but I didn't.
So, this is why we always start low and work up, eh? I noticed an unexpected amount of oil on the first cases but everything appeared otherwise normal until I got two loads below expected max, where I suddenly saw pronounced extractor imprints. After I noticed the obvious imprints, I examined the lower charged cases more closely and I could see very faint extractor marks on almost all of them.
Obviously, I stopped the work up immediately and began investigating. After a discussion with UncleNick and discovering the OAL problem, I went back to the first load that showed the problem and tried again.
Viola! No more imprints.
I was thinking about all those posts we see where someone says "If you're loading over book max, please stay away from my range!" while I was working on this project. I guess those people don't like wildcats much, since there's no such thing as "book max" or even minimum!
Still happily answering to the call-sign Peetza.
You do not HAVE a soul. You ARE a soul. You HAVE a body.
He is no fool who gives what he can not keep to gain what he can not lose.
-Jim Eliott, paraphrasing Philip Henry.