Logan wrote on Aug 8^th, 2025 at 4:59pm:


His suggestion usually works, but doesn't always apply since it can vary as you've discovered. Especially so when a old rifle has a groove diameter that's oddball sized for the normal size chamber. It's not all that uncommon to find old rifles with larger than normal groove diameters that wont accept fixed ammo and chamber. I have a Hepburn in .32-40 that accepts all my .32-40 ammo chambered, but the groove diameter is .328" and it wont accept a .328" bullet seated in the case. I has a Saeco mold opened up at the base band to .328" and had Jerry Cleave build me a breech seating tool to breech seat the bullet and I shoot it this way.
I also have Ballard with a .38-55 Schoyen barrel that's a .384" groove diameter and only gets shot as a breech seater due to the large groove diameter. 
I You may end up shooting yours as a breech seater if you discover a .456"  bulleted seated in a case still wont chamber, or do as Tom mentioned and have a stop ring bullet mold made to make it a heeled bullet and fit the case and bore.

Logan wrote on Aug 8^th, 2025 at 10:08pm:


Odds are if you go less than groove diameter with BP it wont hurt at .001" smaller, but more than that will likely begin to lead the bore. Unless your smaller bullets were paper patched, and then you can get away without leading.

Logan,
Your dimensions make more sense now👍 good luck with your endeavor.

Updates!

I received my case neck turner yesterday and made a couple dummy rounds. Sizing a good inch of the case to 45 ACP then running it through the expander ball and turning. When the wall thickness was turned to 0.010" it still does not fit. Turned to 0.008", still with a 0.458" bullet, it fits! Not real easy by hand, I've ordered a Lee shell holder as that's the only one the tool accepts.

Is 0.008" too thin for the case wall? Wondering if it will crack but I suppose we will see. I can always get a bullet sizer too.

Logan

Alright, after a lengthy hiatus, I've returned to the Military Creedmoor. I've finally found a .456" (groove dia.) bullet sizing die in stock, it should be here any day now. That being said, I had another thought if this doesn't work. I don't really have the time or space to delve into patching bullets and loading with BP right now. Could I just shorten the case until the seated bullet fits in the chamber?

I'm sure accuracy would suffer but it would work, no? Same concept as shooting a 22 short in a 22 lr chamber. May even be a good thing to lessen the airspace in the case as I'll be using smokeless.

Logan