Interesting. I use a very thin film of CLP when I form 257 Rob AI cases. But I do get a funny on say 1 out of 50--by funny I mean that it's formed a crease somewhere.
I did get some shoulder dents fireforming 6.5 Swede cases, all lubed up with hair gel. Never happened before. Maybe a bug flew in the chamber.
I sized the cases, will shoot them, will put a thin coat of lube on them, and they will blow out.
I do the whole danged case as it's my understanding that the case head is forced rearward while the shoulder stays pretty much where it is upon firing.
That is true with a dry case in a dry chamber. But if you lube the case, it will slide to the bolt face and the shoulder will fold out. No case stretch inbetween. I am of the opinion this is why these 308 Win cases are longer than gage maximum after firing. These were fired, by me, in NRA XTC matches, in my M1a.
I lubricated the cases with Johnson Paste wax. The pressures and temperatures of firing melt the paste wax, it acts as a lubricant, just as the wax coating on 276 Pedersen cases. Pedersen's rifle was a delayed blowback and it needed case lubrication or it would not extract with high power cartridges. Pedersen patented his process and it would have worked but the Army was not interested. There were a number of delayed blow back machine guns and light infantry squad weapons that were fielded with oilers on top, but Pedersen decided on wax for his mechanism.
My M1a case life was extraordinary: 23 firings. I retired the cases because primer pockets were getting large. Most M1a shooters fire their brass five times and toss it, because they developed case head separations after five reloads.
This was due to the case shoulder sticking to the front of the chamber and, this is an extremely important concept, the fact that gas guns unlock while there is pressure in the barrel. This effect is called the residual blow back effect, look it up in Chin's Machine Gun series. The purpose of this is to "pop" the case out of the chamber and increase the time period in which there is useful energy to move the mechanism. You can see it in this chart:
The action unlocks, moves, while pressures are less than 650 psia. It might be hard to see, but the velocity is the velocity of the operating rod. The bolt is unlocked which there is still pressure in the barrel and the operating rod is moving backwards, extracting the case. This has the effect of stretching the case head, if the shooter is using dry cases in a dry chamber. However, with my lubricated cases, the case shoulder cannot grip the chamber walls, and so, the shoulder is folding out as the case is extracted. If however, a dry case is fired in a dry chamber, the shoulder is also moved, but the case sidewalls are stretched.
Reloaders using case comparators will measure the base to shoulder distance of a fired case out of a gas gun, thinking that they are measuring chamber headspace. They would be if their rifle was a bolt gun or single shot, but with a gas gun, what they are measuring is nonsense. And you can find all number of threads where reloaders set up their dies with comparators, after measuring cases fired in gas guns. And in that thread, at some point, the reloader is telling all that he is confused why his reloads won't chamber, or extract!. It is because, cases get stretched in gas guns.
