I built a 375-06AI on a Mauser action.
I picked the AI version for a couple of reasons. Dies and a reamer - both were available. I use both 30-06 brass and 35 Whelen brass.
The 30-06 brass is cheap and is not difficult to form into 375-06AI.
(I call mine a 375 Whelen AI - they are the same.). I annealed some of the brass. So far only one case failed and that was when I was learning how to form the cases.
If you’re building your rifle on a controlled feed action, you’ll probably have to open up the rails - I did. If you use a push feed such as a Remington 700, no need for modifying the action.
As far as forming the brass. The first few cases I opened the necks to .416 and then sized the cases in the dies. This method is the method where I lost one case.
The other method, I open the 30-06 necks to .32, then .338, then .358, then .375.
I then loaded ammo with cast bullets, with the bullets run into the rifling. I also used jacketed bullets a couple times, both worked. I then fire-formed the cartridge and I squared the neck in my forester case trimmer.
Most of my cases ended up being made from 30-06 brass because I had plenty laying around.
Last edited by Bugger; 02/18/22.
