260AI Fire Forming Article

[palma]

I was glad to read the 260AI fire forming article as I've been looking for something on the subject for a long time. I did, however, have a question about the false shoulder - cream of wheat method, and have sent the author a PM. I thought I'd raise it in the forums also.

Ok...so doughnuts occur when sizing .243 brass to .260 prior to fire forming. Do the same doughnuts occur when creating the false shoulder by expanding .260 brass to 7mm? If so, is the false shoulder - cream of wheat method really superior to just the cream of wheat method?

 

[rstreich]

...Ok...so doughnuts occur when sizing .243 brass to .260 prior to fire forming. Do the same doughnuts occur when creating the false shoulder by expanding .260 brass to 7mm? If so, is the false shoulder - cream of wheat method really superior to just the cream of wheat method?

I have to add a counter-example to this. I use Lapua .243 brass as the parent for my 260 AI and my thrice-fired brass shows no doughnuts. The one difference may be that I turn my brass and I make sure that I get a solid cut into the shoulder. I also wipe the brass with a little Ballistol for lube when I fireform.

I may be completely off here, but I don't think these are typical doughnuts. That is, I don't think they formed from brass migrating into the neck. To me, it looks more like thicker shoulder brass that became part of the neck when the expander mandrel was run through it.

 

[techshooter]

rstreich:

You have it exactly correct: The thicker shoulder brass is moved into the new and longer neck. This is why your neck turned cases did not form donuts - you removed the thicker brass. Using the false shoulder for fireforming does not change the neck length in the end, and therefore no shoulder brass is moved. The expansion only serves to lock the case in place during the firing pin strike.

Cheers,

 

[palma]

danke