Case deformed during fire forming

C

ciPeterF

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New to fire forming.. this happened to one of the 223 cases I was fireforming into 7mm TCU. The load used for the fireforming was about 15% less than suggested (eg 21.5 gr versus 25). Case was fine before firing..

Curious as to what happened??

thks

peter
 
Why are you fire forming for 7TCU? I just run .223 brass into my 7tcu die and out comes 7tcu brass. The expander ball does it for me.

You may need to make sure your expander ball has some taper, but thats all I do, I've resized hundreds that way, with maybe only a couple of split necks.

As to the deformed case, it looks very much like a hydraulic dent from resizing with too much lube, but don't ask me how that relates to it being fireformed and looking like that, just an observation.
 
Not enough pressure to seal the neck in the chamber. Gas is getting back into the body of the case and giving you the same effect as a major hydraulic dent. As Ted suggests use a load with higher pressure although you may not have to use a book max load.
 
scar270.. my dies do expand the neck, but the shoulder's need a firing to fill in perfectly..

stocker.. that makes sense, there was also some blackness on the case that I cleaned off..

thanks!
 
ciPeterF said:
scar270.. my dies do expand the neck, but the shoulder's need a firing to fill in perfectly..

stocker.. that makes sense, there was also some blackness on the case that I cleaned off..

thanks!
Click to expand...

Hmm, I'll have to compare the ones I just necked up to ones that I've fired, I havn't noticed any difference in mine, and they have shot very accurately.

That answer about the gas coming back around the neck makes sense, thanks for the info on that.
 
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