Did you ever encounter 45 ACP ammo running hotter in your Thompson?

[Doug Quaid]

I mixed up some 45 acp reloads with cast lead round nose bullets from a reputable maker and the max charge of Unique powder from the 2002 Lyman manual.

According to the manual, the velocity should be 905 fps.

When shooting the ammo out of my M1A1, the gun was really jumping much harder than it does with the Speer/CCI bulk ammo I normally buy.

There was plenty of gas blowback and the cyclic rate was way higher than usual.  It was surprising how much more recoil there was.

I loaded the max load because I'm used to shooting 9mm and most 9mm subguns run best on the higher end of the 9mm velocity spectrum.  Also, the load listed in the Lyman manual only showed 16,000 psi pressure, which is much lower than the 21,000 psi maximum, and that pressure would not be expected to harm a tank like the M1A1.

I was wondering if you have encountered this phenomenon before, 45acp ammo running a lot hotter out of the 10 inch barrel than expected.  

It occurred to me that since Unique has a medium burn rate, it might be adding a lot more energy to the bullet if the barrel is long.

I looked at this website and it seems that most 45acp ammo picks up between 50 fps to 100 fps when going from a 5' barrel to a 10" barrel.

http://www.ballisticsbytheinch.com/45auto.html

Anyway, I am going to try the minimum load and see what happens.  This is a good excuse to finally buy a bullet chronograph.

 

 

[Dan K]

Chrono them. PVin=PVout

Keep in mind with book data, you have a specific lot of components at a specific time in a pressure barrel, i.e. cut tight to minimum specs. It does not account for lot to lot variation, different bullet bearing surface areas, primer brisance, etc. 

I run book minimum in my Thompson, runs fine. I run mid range loads in my Uzi and it runs too.

 

ETA: I have an extra chrono here if you want one.

Edited October 7, 2023 by Dan K

[Chip]

I can't find my lyman book, but the other 4 manuals I have show a Max load range of 5.8 to 6.6 grains of Unique with a 230 grain lead bullet.  That's quite a range, likely to Dan K's point regarding powder lot and component variations.

Edited October 7, 2023 by Chip

[shadycon]

I run 6.6 Unique /230gr lead or FMJ in my rebuilt semi-auto with no problems. I like to see a bullet  not just bounce off a hard target. I have picked up factory loaded bullets that could be reused after hitting an old washing machine at 50 yds.