What should the base of a .220 rocket case measure after fire forming? Swift case measures .440" before fire-forming.

Thanks, any help will be apprec.

Bill

Help me understand what part of the cartridge case is the "base"? Be specific if your talking about the head of the case then is it the rim, ahead of the extractor groove or the expansion ring?

The .220 Weatherby Rocket is an improved Swift.

I know what the rocket is, I have one. After the case is fired in the rocket chamber, the area(above the web-expansion ring) will mike .448". The Swift case before fire-forming will measure .442". The CH(4D) die(Full length) I have is only .438 at the opening. So, when trying to size, the dies will start to peel brass off the case. I am not sure if the chamber is too large, or the dies are too small? I am thinking the dies along with 3 fired cases will be returned to 4D to correct. From what I can find out on the Rocket, it should be in the area of .447" at the expeansion ring.

Hope this will help you with my problem.

Bill

It sounds like your FL sizing die is grossly undersize. If the unfired, new case is .4420", the die should not be trying to reduce it .004" below factory new specs.... The dimension drawing for the .220 Swift case indicate that the max. case dia. just ahead of the extractor groove is 0.445".

The die has to size below the std case diameter to ensure it fits all chambers. The brass will expand a little when sized, just as brass shrinks a little when pressure drops from fireing allowing it to be extracted.
I agree .004 sounds excessive but if the factory case mics .440 and the die is .438 thats only a .002 differance, not a whole lot. This could very well be in spec of the cartridge.
If the die shaves brass when you resize I`d be more concerned that the die was scratched or dirty. I`ve sized brass from quite sloppy chambers with no sign of shaving or scratching. You might try cleaning the die and polishing it lightly with a bit of oiled 0000 steel wool on a bore brush spun slowly with a coreless drill or dremal tool. My thoughts are if you plan on sending it to be opened up a bit of polish can`t hurt and may just fix it.