Fire forming 303s into 444s

[mattd]

Not having much luck. My 303 is mil surp, converted from berdans. 9g of unique seems to be the magic number. Less and they don't form fully. Even at 9g there is slight gas leakage around the boxer primer (converted from berdans by drilling out the cup of the primer, leaving the sides so that a boxer fits).

The couple mil surps I did split at the neck, even being annealed. The 2 commercial brass I did worked great, but they are still a little tapered in the middle. And they are short like hornady 444s, LAME just like hornady 444s
100653

Maybe I'll just see about trading the berdsn 303s for real 444s

[mikeym1a]

Seem like you need an inside neck expander to open it up first, then anneal, then try fireforming. But looking at the cases, the .303 is about .045 smaller in diameter than the .444 at the head. Unless you were gonna put a shim around it, getting stock brass might be better. Not sure how available .444 brass is, but, if it's a bit rare, look up CustomBrassandBullets on the net. Decent prices.

[Tackleberry41]

Ive had good luck forming 303 into 410 shells. And 444 into 410, but they never lose that reverse bottle neck, guess brass is just to thick at the bottom. Another case to look at is the 9.3x74r or one of the shorter ones. Thought they made a 62r.

I know 444 marlin brass is nearly unobtainable for whatever reason right now, what is available is way over priced.

[jonas302]

I think I would hold out for 444 brass it comes up here sometimes at a real good price

[lar45]

I really like the Lee dies for expanding necks on stuff. The expander button has a nice long taper and is really smooth.
How do they look after a full pressure load?
If you want to keep the base centered when fire forming, you can cut a thin strip of masking tape to go around the base to make a snug fit in the chamber.

[sawzall]

I've thought about trying this as I had a fair bit of 303 brass. I thought maybe using my Harbor Freight mini chop saw and cutting some bushings from 45 acp brass. Once fire formed I'm positive it would stay put. My thoughts are the original case would expand and forma small step in front of the bushing to hold it in place. Then I found some 444 brass at the local gun show and sold the 303 brass instead.