Excessive Pressure

[dvraa]

This happened back in 89' I was younger and a little dumber and pretty broke raising 3 kids. I was shooting and reloading for my Marlin 1895 in 45/70. I shot this rifle a LOT, still have it and it's had well North of 5000 rounds through it .
I picked up a Hornady loading Manuel at a garage sale and found a load listed for 45/70 that looked fantastic. The top load listed was 300 grain jhp 50.6 grains of IMR 4227 with a muzzle velocity listed at 2400fps. I started low and worked up to 50 grains even, it shot fantastic, 3 shot cloverleaf groups at 100 yards. What it did to deer should have been declared a war crime. I'd shoot one in the lungs and you could put your fist clean through the deer.
I happily ran around 4-500 round of this load through my rifle without a hitch, shot everything from gophers, fox, squirrels and deer. I bragged about this load to my shooting friends and a couple gun smiths and several of them voiced grave concerns.
One day on a whim I called IMR powder labs and was able to talk to Bill Coles the head guy there. I told him about the load I was shooting and he also was alarmed. He said they normally didn't run customers loads through their pressure barrel but he told me if I promised not to shoot any more of them for the time being, he'd make an exception. He had me load up 10 rounds in new brass and send them in to him.
Two weeks later I got a phone call from him and later this letter and pressure sheet . I was shocked to say the least. I never had a sticky case or a blown primer.

 

[dvraa]

As you see they stopped after the 5th round. I kind of wish they had shot all 10 rounds but I suppose at 63000+ cup they didn't think any more abuse of their pressure barrel was advisable.

 

[Webster]

This happened back in 89' I was younger and a little dumber and pretty broke raising 3 kids. I was shooting and reloading for my Marlin 1895 in 45/70. I shot this rifle a LOT, still have it and it's had well North of 5000 rounds through it .
I picked up a Hornady loading Manuel at a garage sale and found a load listed for 45/70 that looked fantastic. The top load listed was 300 grain jhp 50.6 grains of IMR 4227 with a muzzle velocity listed at 2400fps. I started low and worked up to 50 grains even, it shot fantastic, 3 shot cloverleaf groups at 100 yards. What it did to deer should have been declared a war crime. I'd shoot one in the lungs and you could put your fist clean through the deer.
I happily ran around 4-500 round of this load through my rifle without a hitch, shot everything from gophers, fox, squirrels and deer. I bragged about this load to my shooting friends and a couple gun smiths and several of them voiced grave concerns.
One day on a whim I called IMR powder labs and was able to talk to Bill Coles the head guy there. I told him about the load I was shooting and he also was alarmed. He said they normally didn't run customers loads through their pressure barrel but he told me if I promised not to shoot any more of them for the time being, he'd make an exception. He had me load up 10 rounds in new brass and send them in to him.
Two weeks later I got a phone call from him and later this letter and pressure sheet . I was shocked to say the least. I never had a sticky case or a blown primer.

You did what a lot of guys do. You tried to shoot as close to max load as you thought was safe because you didn't have pressure signs. As everyone says the manual are just a guide every rifle is a little different. Bore dimensions, freebore, throat ect. Did you get good accuracy with maybe 1 or 2 grains less powder?

I think we are all shocked by how hot the loads can be and not always have indications of pressure. I am lucky I can always judge pressure by primer cup appearance and ejector smear marks in both my rifles.

 

[dvraa]

It's been a lot of years since this happened so I don't remember how the groups were with a lighter load. The 50.0 load though was EXTREMELY accurate I'm my rifle. The primers were flat but had a radius around the edges, fairly normal for my rifle. One old gunsmith friend of mine said he figured the sides of the case where clenching the chamber walls on firing if that makes sense.

 

[Old Navy]

Pure luck makes more sense!

 

[Krogen]

Thanks for posting this. For years people have discussed various ways of judging pressure. Pressure "signs" abound, but many of us have been fooled by false overpressure signs or very hot loads that don't show signs.

Certainly things like hard extraction, blown primers, scuffed case heads or exceedingly high velocities point to problems and we ought to pay attention. The absence of these "signs" doesn't mean we're good to go.

 

[M-61]

One old gunsmith friend of mine said he figured the sides of the case where clenching the chamber walls on firing if that makes sense.

Not only does it make sense, it is exactly what should happen. It is why the case and the chamber should be clean, meaning NO oil or grease. Clean.
It is one of quite a few things that take place when the cartridge is fired. The case momentarily grabs (clenching) the chamber walls. That momentary action prevents the cartridge from slamming, with full force, into the bolt face testing the strength of your locking lugs. Of course the case springs back from this death grip on the chamber walls, and allows extraction to work.
The Brits proofed their rifles with big over loads, but the final test was a coat of oil on the case. If it didn’t blow up, it passed.

 

[Murray Brook]

It's unfortunate that we don't have an accurate and inexpensive way to measure pressure in our own chambers. Just because it was 63000 cup in their test chamber doesn't mean it was that in yours.

 

[Webster]

It's been a lot of years since this happened so I don't remember how the groups were with a lighter load. The 50.0 load though was EXTREMELY accurate I'm my rifle. The primers were flat but had a radius around the edges, fairly normal for my rifle. One old gunsmith friend of mine said he figured the sides of the case where clenching the chamber walls on firing if that makes sense.

I consider any load 1 to maybe 2 gr under max published a hot load no matter what the results are and the primers look like. Sounds like a hunting rifle. There is no reason not to shoot a mild load. It's probably accurate enough and it will certainly kill a deer.

 

[Rock Knocker]

I need to get me an old Marlin!

Ive just got interested in getting shotshells pressure tested. Ive loaded for rifle and piston for awhile now but this shotshell thing is different. Trying to make up to 2oz buckshot loads and fire that with basically a pistol powder can get wild quick.