7.8x19mm- Closer, But No Cigar

So the finishing chamber reamer I ordered was supposed to arrive today, and with minor modification I would have been able to ream the chamber. Sadly it did not arrive, and tracking now says it will arrive Monday. I’m not a patient man, so we’ll get back to that shortly…

One thing that was needed was for the gun to be .30 caliber, which meant lining the bore. I had a short section of .308 Winchester barrel rifled 1:10. A little research showed that .30 Luger also used a 1:10 rifling pitch and shoots bullets in the same weight range as the 7.8, so I figured this would work fine. I turned the section down on the lathe, then drilled the barrel through from both the chamber and muzzle ends. the liner was a gentle press fit. I slathered it in Loctite Red and pressed it in. Voila! .30-caliber Helwan.

Of course I’d still need to cut the chamber, and ordered a .32 H&R Magnum chamber reamer, which ought to be easy to modify for my purposes. Thank you, Patreon supporters! This is of course the very reamer that did not arrive on schedule today.

Earlier in the week I was dialing in my process for making cartridges. It all starts with the .30 carbine brass.

Sizing the brass using a .32 H&R Magnum resizing die. The case is not straight-walled, and it needs to be.
After running the brass into the die it’s mostly straight-walled, except for a bit at the base. Got to do something about that…
The lathe solves the problem. Of course it wasn’t that simple…

Brass needed to be removed at the base of the cartridge using the lathe, and there was definitely a learning-curve there. It also required making a special mandrel to fit the brass. First batch of five saw three fail, but by the end I was five for five. I wound up with a total of 25 cartridges. Good enough to start.

For test purposes I loaded 78gr LFP bullets over 3.0gr. and, after some consideration and calculation, 3.5gr. of Unique, so I had some loads to test. The goal was to drive a 75gr. bullet at 1150 fps. The math suggested I could drive it as fast as 1200 fps. without creating mechanical issues with the gun, but I saw no reason to push it that hard.

Finished ammo, 78gr LFPs over 3.0 gr. of Unique.

When I discovered that the reamer would not arrive today, and seeing as I had all of this ammo on-hand I sacrificed a .375″ chucking reamer to make my own chamber reamer.

My improvised chamber reamer. It’s ugly, but it works. Mostly. Sort of.

So I used my improvised chamber-reamer until the loaded cartridges fit easily. I used a carbide burr to cut the feed ramp, then cleaned it up with a 400grit sanding drum and a cratex polishing cone.

After tweaking the feed lips slightly the magazine presents the cartridge nicely and they chamber properly.

OK, all ready then. The rounds fit the chamber, they feed from the magazine, they extract and eject manually. Time to shoot. I set up the Caldwell Chronograph. The 78gr LFPs over 3.0 gr. of unique produced 1021 fps. for 181 ft./lbs of energy. Not bad, but far below potential. Now it gets sub-optimal- the gun cycled, but did not extract the fired cartridge. It also didn’t push the slide far enough to engaged the magazine hold-open.

Maybe the 78gr. loaded with 3.5gr. of Unique will have what it takes? Nope. It made 1147 fps. and 228 ft./lbs but again, the cartridge did not extract. On the other hand it showed no signs of excessive pressure, and the gun seemed to be handling it just fine. I decided it was time to be stupid. I loaded some 100gr LFPs over 3.5gr of Unique. This yielded 1086 fps. and 261 ft.lbs. Outstanding… but it still didn’t extract.

After looking over the gun carefully, I think the culprit is a sticky chamber. It is snug, and is not the smoothest so I am going to wait for the proper reamer, which is a few thousandths larger than my home-made reamer.

The 100gr. bullets certainly didn’t lack penetration. They passed through 16″ of Clear ballistics 10% ordinance gel, then through a 4×4 and retained enough energy to do this to a .50-cal ammo can.

When the cartridges extract properly that will change a number of things; the slide will get more momentum transferred to it for one thing. If the pressure is too high when the slide opens it could blow the case-head. I don’t think it will, but it could. Once the chamber is properly finished we’ll see what’s what.

In the meantime if anyone has any .30 Carbine brass laying around that they’d care to contribute…

Michael Tinker Pearce, 29 January 2021

If you like what you see here, please consider clicking the link above and supporting me on Patreon.

Advertisements

Leave a Reply