.45 ACP Pressure Problems

[dam555]

Today I tried some 230gr cast boolets in my semi-auto Thompson, fired 5 rounds and then checked ejected cases, 3 out of the 5 had flattened or missing primers. Load was 4.1 grains of RedDot. I have used this load in my 1911 with no problems. I'm wondering if the crimp was too tight. These were loaded before I got a Lee Factory Crimp Die. Any other ideas?
Thanks, Don

[HeavyMetal]

Just because a load works well in one gun does not mean it should work well in all guns!

The first manual I found on my desk was the Lee one. it show 230 gr j types at 5.0 grains Reddot and 230 grain lead at 4.0 reddot.

Thinking that bore diameter, boolit diameter, throat, head spacing could all be a little different in the Thompson I'd reduce the load or try something else.

But first I'd double check everything! Lee says the 4.0 reddot load only generates 12,800 PSI That should not have caused your problem. Start checking and then proceed when you feel both the load and the rifle check out.

[BD]

I'd chamber one, then eject it without firing it and re-measure OAL. One big cause of pressure increases in the .45 acp is the bullet being set back into the case.

BD

[MtGun44]

+1 on both posts above.

You need a solid taper crimp to keep from pushing the boolit back, and
there are huge differences in chambers and bbl dimensions and just
because the load is in the book is NO WAY a guarantee that it is safe in
your gun.

This concept is the most fundamental one in reloading and I am surprised
at the number who seem forget it.

You ALWAYS need to load down to the starting load and work up for a
new gun until you have enough experience to know that the particular
gun "acts normally". They do not all "act normally".

Bill

[Willbird]

I have never heard of missing primers as a pressure sign. it sounds to me like the primers are coming out of the pockets for some reason, did they seem to fit tightly when you seated them ?? Typically excess pressure in 45 acp leads to bulged brass. But in a semi thompson I'm not sure how large the feed ramp is.

Bill

[JW6108]

I have never heard of missing primers as a pressure sign. it sounds to me like the primers are coming out of the pockets for some reason, did they seem to fit tightly when you seated them ?? Typically excess pressure in 45 acp leads to bulged brass. But in a semi thompson I'm not sure how large the feed ramp is.

Bill

With high pressure, primers can expand sufficiently to stretch the pocket so that it can no longer hold the primer in place.

[dam555]

The primers were seated using a Lee hand primer and required a normal amount of pressure to seat them, I am going to pull down some loads and verify the powder and weight.

Don

[StarMetal]

I have one of those Thompson and they have a funky firing pin system on them. I think they rather chew up the primers pretty bad. Now I've fired all kinds of loads, bullet weights, and configurations in mine and nary had a problem or one that even showed high pressure.

For those of you that don't have the semi Tommy guns they have a rectangular firing pin hole except the short edges are rounded not square. The firing pin is a big long stamped out affair and I'd say the portion that fits through the firing pin hole is at least 3/8 inch wide and it had a little raised numb on it that is the pin. During bolt recoil the pin actually protrudes through that slot some distance, like 1/2 inch. I talked to Kahr about this as to why Auto Ordnance designed it like that and they said they hadn't a clue. They didn't like it either.

I'd try what was posted above see if the bullet is loaded out to far or is getting pushed back into the case. You all know I'm not a believer in taper crimps on any cartridges. The case should have enough neck tension and you can, contrary to popular belief, rollcrimp a 45 acp. NRA had a whole article on that in there Cast book.

Joe

[Willbird]

Star, is the throat such that you can headspace on the bullet ?? Does the firing pin also work as the ejector ?? I recently heard of a browning design pistol that works like that. Taking a quick look at an MAB pistol I have here it looks as though the firing pin functions as the ejector.

Bill

[StarMetal]

Star, is the throat such that you can headspace on the bullet ?? Does the firing pin also work as the ejector ?? I recently heard of a browning design pistol that works like that. Taking a quick look at an MAB pistol I have here it looks as though the firing pin functions as the ejector.

Bill

No none of my bullets touch and no the gun has the regular Thompson ejector.

Joe

[JW6108]

With high pressure at firing (not seating), primers can expand sufficiently to stretch the pocket so that it can no longer hold the primer in place.

[dam555]

Checked the powder load and OAL, both were ok, fired a couple in my SA MilSpec and they were fine, so fired some more, no signs of overpressure so it must be the way the Thompson chambers them. Thanks for the help. Don