Oddball Cartridges and How to Make Them (Sometimes)

This post is brought  to you by a friend having bought an old German single-shot rifle chambered for 8.15x46R: 8.15 millimeter bore and a 46 mm long, rimmed, case.

https://commons.wikimedia.org/wiki/File%3AMunit07.jpg

No, I'd never heard of it either.

So now my friend has this lovely old boomstick with no ammo to be found for it. The saving grace of this is that it's a cartridge that can be made by taking a cartridge case that's close enough, and using the sizing die from a loading set to form it to the right shape,,, or at least close enough (which I'll explain later).

Making .300 Blackout from .223/5.56
First, I'm going to use a much more simple example.

1) Take a .223 case and trim it.

2) Lube it.
3) Run it into the sizing die.
4) Trim to final length.

(Read this post for a more step-by-step description of the process.)

Family photo:

L-R: .223/5.56 cartridge, trimmed cartridge, resized .300 Blackout cartridge.

For a lot of cartridges, this (sometimes with a little variation) is all it takes... but then you get to something like that oddball 8.15mm. 

Making  8.15x46R from .30-30 Winchester

Fortunately, the recommended case to start with (.30-30 Win) is an easy one to find. But we'll have to do several things to it to make it fit:

1) Cut it to approximate length (a little too long is better than short).

2) Remove any burrs from the new case mouth.

3) Lube the case, both the entire outside and the inside of the case neck.

4) Run it into the sizing/depriming die.

It comes out looking like the picture on the right. ->

That's the easy part, and often the only part. Some cases will need to be trimmed to final length (if they're a bit long) and deburred. After that, they're ready to load. Then, the first time you fire it, the heat and pressure will fire-form the brass to the chamber, and -- since it's a single-shot rifle -- you'll probably never need to resize it again. 

But not here, oh no. Because there was a lot of variation in these rifles, sometimes it needs more steps. 

5) The rim of the case was a little too large in diameter, so it needed to be cut down a bit. In this case. I took a coarse file and, holding it steady, dragged the rim down it while rotating the case to take off a few thousandths. 

6) Try it until it's right. In this case, it reduced the diameter from the standard .506" to .486".

7) At this point we discovered that the rim was a bit too thick for his rifle. To thin it, we used a piece of 220-grit wet-dry sandpaper on a thick piece of glass. Use plenty of water on the paper, work the base in a figure 8 pattern, then turn it in your grip a bit and repeat. (Yes, it's a slow process.) The original thickness was .063"; now it's .040" and the action closes on it snugly.

Yes, it's a lot of work for just one cartridge. We're going to find a small lathe to use, which should make trimming the diameter and thickness of the rim a lot faster. He'll never have a lot of cases, but they should last a long time.


That's the basic course in forming brass for a new use. In some cases, the actual forming is far more involved since the difference between the original case and the thing you're after is drastic enough that the forming has to be done in steps. 

For some old black-powder cartridges, there are companies that make, say, a '.45-caliber basic' case; it's long enough and large enough in diameter that with the correct dies you can form it to a number of different cases. And with most of these being for single-shot rifles, take care of these cartridges and they'll last many firings, so it can indeed be worth it.