bigedp51, thanks for the explainations and the trouble you've taken here. Of course the process of fireforming with o-rings brings up a question.
After the case has been fireformed, and the bolt is closed on the round, the case is pressed into the chamber, thus shrinking the round. When locking the bolt, the bolt head comes back a couple of thousands. Wouldn't that create room for the case to stretch again? Or do you keep using the o-rings while shooting?
The two "standard methods" for fire-forming cartridges cases is seating your bullets long and contacting the rifling, this holds the case against the bolt face and prevents case stretching in the web area.
"PROBLEM" the Enfield rifle fired cordite powder and a used Enfield rifle will have throat erosion and you can't seat your bullets long because there is NOTHING for the bullets to touch.
The second method is making a false shoulder on your cases and letting them headspace on the shoulder while fireforming.
Below is a 30-06 cartridge case used just for the purpose of showing what a false shoulder would look like. The problem with the false should method on the .303 Enfield is it stretches the necks and causes split necks unless the necks are annealed.
If you fireform your cases using the o-ring method the shoulder of the case will be blown forward and the case will headspace on the shoulder of the case and hold the case against the bolt face. Just like a normal bottle neck case that is neck sized only.
Below the o-ring is holding the case against the bolt face.
Now after fireforming the case is held against the bolt face by the repositioned shoulder of the .303 case and the o-ring is not needed.
Once you understand that the present day commercial .303 ammunition is not made to military standards, and the SAAMI reloading dies do not conform to the Enfield military chamber dimensions the battle is won. Just neck size only and if needed you can use a .303 case forming die to just push the shoulder back without changing any other case dimension.
Below a case forming and trim die in .303 British, the case can be pushed into the die with just your fingers and stops when the shoulder of the case hits the shoulder of the die. (shoulder bump die)
