Home Forums Hunting & Shooting Ask The Gunwriters Question - recommend COW load for fireforming

I use the Lyman M expander die to form .35 Whelen from .30-06 with no problem, just lube the inside of the case necks well.

So far, so good. L to R is a fired .30-30 case, two cases run over an 8mm expander ball and a .357 Magnum neck flaring plug and finally a factory 38-55 case. The .357 plug was run in as far as it would go, the case mouth flaring is from the full diameter stem of the plug. A.375 plug should fit in but if not the cases can take a trip over the larger Lee universal expander plug to flare them out enough.

I was a bit surprised how little handle pressure it took to expand the brass using nothing more than RCBS II case lube in the necks. The .38-55 dies won't have an expander ball to run all the way through that constriction, just a plug like the pistol dies, but it should have a longer shank. Tracking indicates that the 38-55 dies will be here Thursday so I'll find out one way or another. As long as a bullet can be seated deeply enough to chamber the first firing will straighten the walls out completely. They'll be a bit short but that won't be a problem. Fun stuff.

I was thinking Trail Boss too. Like 11 grains

I just made up a little more than hundred 375 Whelen AI Brass. Most were from 35 Whelen, piece of cake.
I also opened up 30-06 brass just for the heck of it since I had some miscellaneous brass laying around that I wasn’t going to use in an ‘06.
1. First open to 8mm
2. Second opened to .338
3. Third opened to .358
4. Fourth opened to 375.
Then fire formed with cast bullets.
No losses...