just got some 375 h&h brass that I want to fireform to 458 lott. I heard of cream of wheat and pistol powder....does anyone have a load that they have used to blow out the 375?

Jason

10% was running through my mind. So did a search and this if from Howell's book.

by Dr. Kenneth Howell in his book designing and forming custom cartridges.

He recommends starting with the 10% rule
Take the parent case with a fired primer still intact
Fill the case to the top with Bullseye (or similar speed fast pistol or shotgun powder)
Pour powder onto scale and weight
Divide the total weight by 10
If for example, your total is 63.40 grains.
Your starting charge should be ~ 6.34 grains
This will fill up your parent case about 10% of it’s total volume

When ready to form, start with a PISTOL primer, NOT a RIFLE primer

Add your forming charge
Then using a small wooded dowel that will fit through the case neck, lightly tamp a quarter of a sheet of folded or wadded up toilet paper onto the powder at the base of the case.

Then fill the case with your inert filler material
( Cream of Wheat)
Leave ~ 0.100” of the case mouth open so you can top off the case with a retention material like lead bullet lube or paraffin wax
Just “smear” off the top and wipe away any excess around the outside of the neck

I thank you sir

I have been searching these forums and will have some fun fireforming some brass. I am going to also try some 300 win if they work I will trim them to .458 win

Jason

Sounds like an awful lot of work unless you can't find .458 wm or Lott brass.

I have used the method Ken Howell described, with a twist, for over 50 years. The twist is that I do not put anything on top of the 1/16th sheet of single ply toilet paper, and I use rifle primers. Has worked perfectly for me for more than 5 decades. My powder for such forming is always either Bullseye or Nike. If the first time you try it the cases(s) don't quite fire form fully, increase the powder charge a few 10ths of grain. Different makes of brass are less "formable" than others due to different brass and different heat treat/annealing in manufacture.