I am picking up a .450 Ackley this friday. I have 50 cases of 375 Weatherby brass I want to fireform into the .450.
I have no way at this time to expand the necks larger than .416.
Using cream of wheat,paper over powder wad and a wax plug is looking like my best bet.
Question....
I have no idea how much pistol powder to load this size case with to blow it out properly.
Any suggestions would be appreciated.

Thanx Don

I use the tissue paper, corn meal and wax plug on several wildcats including, 270 Gibbs, 450 Alaskan and 338 Jarrett. All of these work well with 18 grains of Bullseye. I would try this and if the shoulder isn't fully formed go up .5 grain at a time. I would recommend that you use new brass. Fired brass unless it is annealed will usually split at the shoulder.

Thank You.

I loaded 30 cases. Will try them out as soon as I can.

Thank you again.

Ended up using 20 grs. Of Bullseye.It blew out the case perfectly.

Tried a quick load at the range just to get a feel for the round.

500 grain Hornady SP with 79.0 grs. of H335. There was still space between the charge and bullet base.

For 5 shots I got an average of 2280 FPS.

Good to hear that it worked well for you. I definitely prefer using this method for cases like this. If you neck up the case it always seems to end up with an uneven neck length. This way they come out nice and even.

I shot the fire forming loads straight up in the air.
I read some where that if you shot straight up the necks would be more uniform.
They were right. Almost perfect.