I have no experience with fireforming. Someone gave me a box or two of 300 H&H ammo. I have a 375 H&H rifle. I understand that 300 brass can be fireformed for use in the 375. Do I need to disassemble the ammo into components, reload using pistol powder, etc or is it safe to just fire the undersize bullets right down the 375 barrel and fire form them as is? Thanks, "D"

D Hunter,
That is way more trouble than it is worth. Sell me the 300H&H ammo and buy a bunch of 375 brass. It's pretty cheap at Midway. What are the specs on your 300 ammo? Thanks, Bob

I agree with VFR, cheaper and easier to purchase the correct brass.
However, if you insist on modifing 300H&H brass instead, anneal than expand the neck, size in the 375 die, load using standard 375H&H data and shoot. Initional headspace is controled by the belt, so forming false shoulders and other fireforming tricks arn't necessory.

VFR I will gladly sell the cartridges to you. I will look to see how many I have. They are old factory loads. I will let you know this evening any additional info. "D"

VFR they are winchester loads. They have a slight hollow point. I have almost a box. 18 cartidges. Make an offer. "D'

Instead of fireforming,buy very cheaply once fired 375H&H from many sources on the web. - Lew