9mm Major Problem

[Airic]

Last weekend a friend of mine had multiple case failures in his STI 9mm major open gun. The gun was blowing out the bottom of the case at the rim or just blowing the rim of the case off completely. The ammo was tried in two other STI open guns and produced the same results. I gathered a sample of his ammo and brought it home with me and here is the load:

MG 124gr 9mm projectile

7.0 gr AutoComp powder

Brass was in good order, no cracks or problems with any of them

Primer appeared to be a Winchester Small Pistol (He wasnt sure, ammo was a common load for another local shooter)

OAL was 1.155

I'm not looking for comments on why you would keep shooting if you even get one case failure or why he doesnt know what primer it is. I'm just trying to understand the problem so that I can steer him to a load that will be safe for his gun. So that being said:

Any idea by looking at this load data what might cause this? I was thinking it had to be the Win SPP because I always ran small rifle in 9major guns. Would the primer blowing out also cause the case to blow out?

[EkuJustice]

A SPP won't do that to a case. Has he checked for major setback? That load isn't too bad and shouldnt be causeing the issues he is having.

Without knowing what primer even he has in his loads he dosent really sound like a very experienced or careful reloader. If that is the case, then 9mm Major probibally isnt the place for him to be loading. Not trying to insult or discourage the shooter but 9mm major isnt a load for the inexperienced

[Airic]

A SPP won't do that to a case. Has he checked for major setback? That load isn't too bad and shouldnt be causeing the issues he is having.

Without knowing what primer even he has in his loads he dosent really sound like a very experienced or careful reloader. If that is the case, then 9mm Major probibally isnt the place for him to be loading. Not trying to insult or discourage the shooter but 9mm major isnt a load for the inexperienced

I think I know what your talking about but will you explain what you mean by "major setback"

[mitchiepinoy]

Crimp too hard

[EkuJustice]

Bullet jams back into the case upon chambering causing OAL to become shorter.

[HoMiE]

Crimp too hard

I would think not enough crimp might be causing setback which would reduce OAL and cause higher pressure.

I would work a load with a chrono, even taking someone else tried and true load, start below and work up.

[mitchiepinoy]

But its weird... Maybe he need to lower down the powder charge. And work it up.. My 9mm major KKM with BRAZOR TC 124 AC i reached 168 at 6.4gr of HS6

[EkuJustice]

The load he used is in the ballpark for what others are using for major. My glock is doing it with 6.8 grains of autocomp at 1.145 OAL and zero pressure signs at all. That load shouldt be blowing the backs off cases uless its overcharged or the bullet is set back

[Airic]

forgot to add it chronoed at 1450fps avg

[al503]

I would:

1. Ask him to measure the OAL of a bullet and then push the nose of the bullet down firmly into the bench with his thumb. See if the OAL changes. If he's loading to 1.155" with a MG bullet, there should be enough case mouth tension to keep the bullet from setting back, but you never know.

2. back down the charge and shoot for around ~1375 fps.

3. Increase the OAL from 1.155" to whatever will fit in the chamber without engaging the rifling. He should be able to go up to about 1.2" As long as there is some room for the bullet to jump at ignition, loading longer will decrease the initial pressure spike.

[yoshidaex]

Has any of the brass been roll sized?

[vernbo]

The gun was blowing out the bottom of the case at the rim or just blowing the rim of the case off completely. The ammo was tried in two other STI open guns and produced the same results.

how did that conversion start "I have this load that is blowing the rim off of the case want to try it in your gun"

[Glockman1000]

Has any of the brass been roll sized?

You should look in to this as well as what type & how many times the cases have been loaded or if they were once fired. Also, was the powder confirmed to be AutoComp? I would assume you have pulled some of those rounds & verified the powder charge on another scale? I've gone up as high as 7.4grns of WAC in my open Glock that chronoed in at 194PF with the same bullet.

[Don_B]

"MG 124gr 9mm projectile

7.0 gr AutoComp powder

Brass was in good order, no cracks or problems with any of them

Primer appeared to be a Winchester Small Pistol (He wasnt sure, ammo was a common load for another local shooter)

OAL was 1.155"

I have been shooting 9 major for about 5 years and right away I discovered that the brass is the most important thing to watch. That is the one piece of information that you do not have. Many brands of brass are too soft to use for major.

I would first look at the type of brass that is being used.

[NogNog]

Velocity of 1450 FPS for 9-major with OAL of 1.155 is asking for trouble IMHO. That's in the 181PF with a short OAL. I load AC 7 grains but with OAL of 1.170 and runs around 174 PF. I suggest lower the charge and go as long as the chamber will take.

[BMartens]

This load blew out cases in three guns? The load that is listed should work in just about any 9 major open gun. That means the load listed is not what you are shooting. My guess is you have 7.0 grains of something other than WAC. There are a number of powders that would be quite dangerous at 7.0 grains in a 9mm case. Rule out setback and you have the wrong powder in those loads.

[lcs]

1450FPS with a 124Gr is 180PF. A 124gr bullet builds a lot of pressure with that much powder. Why ? The heavier the bullet, the harder it is to push down the barrel. A 115gn would not be so bad at 1450FPS.

Take on of his loads and see if you can twist the bullet in the case, see if you can push on the nose of the bullet and see if it pushes back into the case. See if you can pull the bullet out of the case with your fingers. If any of these conditions are present--The load is wrong.

If the case is not holding the bullet tight enough-The bullet goes up the ramp and can be pushed back in the case EXCEEDING safe pressure levels and blowing the case apart.

I experimented with WAC and when compressed it develops high pressure. What do the primers look like on the fired cases?

[Hi-Power Jack]

forgot to add it chronoed at 1450fps avg

Airic, you don't need to load that fast (PF 180) - you

should be able to load that down to PF 170.

BUT, even PF 180 shouldn't be causing that problem.

"As others said - it's either:

* not WAC

* not 7.0 gr

* the bullet is being pushed into the case on loading

I had three of the same problems two years ago - never found

out what the problem was, but haven't had the problem since

But, I know that 2 of my 3 problems were all with WW brass - don't

know why that would be a problem, since I use a LOT of WW Brass, but

they were.

Good luck solving the problem.

[BillChunn]

As already mentioned, brass just does not survive as long in 9mm Major. Coming from shooting .38 Super where I could get 4, maybe 5 reloads out of the brass and going to 9mm Major the lifespan is much shorter.

I was using range-pickup brass at a local "lost brass" match and had the same result with my SV barreled gun. Case blew out right at the rim causing the magazine to be sent completely out of the gun. Not fun. Black powder smudges on both hands and a new "case hardened" color job on the top of the beavertail behind the hammer....

Went with new Remington brass at the next local match and did not have a single problem.

I'm loading 6.8 grains of AutoComp under a 124 Montana Gold and Winchester Small Rifle primers, OAL is 1.15 with a .378 crimp. Chrono at 1400 to 1420 fps for a powerfactor of 173.

HH