Primers Backing Out of Rounds in Cylinder?

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9mmepiphany

9mmepiphany

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I was shooting a match (ICORE) with a friend over the weekend and he had a malfunction come up that I'd never seen and can't quite figure out.

He was shooting, .38Spl loaded with 158gr FPRN (looked a lot like Xtreme), in a 686 in DA when his hammer stopped moving . He was still pressing the trigger and it just jammed. As he continued to apply pressure, the hammer finally fell (after about 3 sec) and the shot went off.

We couldn't determine which case it occurred with as he continued to run the CoF, ejecting spent cartridges as he went. The cases were gathered by another squad member.

We discussed this later and it still has me stumped
1. It only happens occasionally....maybe 5-7 times in the last year
2. The ammo is commercially loaded
3. The cases are new Starline
4. It does NOT occur with an empty cylinder
5. It does Not occur with match ammo loaded in once fired W-W cases

I figured if it was a burr on the action that it would occur all the time or at least more frequently.

I was thinking it might be a burr on the rim of the case, but wouldn't that drag all the time?
Could it be a primer backing out and what would cause it?
Anyone every encounter this previously?
Anyone have any ideas of where to start looking?
 
Primer backing out on factory ammo would be unusual. That is a sign of excessive pressure. I had a similar problem with a revolver on 2 occasions. One was a tiny bit of unburned powder under the ejector star. The other was the ejector rod backed out a tiny bit and caused the cylinder to bind.
 
Brass sticks when its being pushed back into the chamber. Place empty brass in cylinder . Point muzzle up. Rotate cylinder , slow double action. Brass drops down and then is pushed back.

Not common, but had it happen. 20190225_215948.jpg
 
gunlaw said:
Primer backing out on factory ammo would be unusual. That is a sign of excessive pressure.
Click to expand...
You're backwards, it's a sign of insufficient pressure to reseat primers. All primers in a revolver back out against the recoil face on firing, and are reseated as pressure forces the brass back over the primer.

This is why revolver blanks, or very light rounds (ie rice shot for insects) need to have flash holes reamed out; it reduces primer backout.

Edit: ah, I see @Varminterror beat me to it.
 
I wouldn't expect this of Starline brass, but is it possible that a loose primer pocket would allow a primer to back out.

The loads were pretty light. For ICORE they only require a power factor of 120. He was shooting commercial reloads from one of his sponsors (Redline) and they usually run at least that hot
 
Yes, I have two different threads going.

This one in Reloading and the other in Revolvers...looking to tap into the expertise/experience in both areas
 
Primer pockets don’t have to be loose to allow the primers to back out. All primers in all firearms do, they are simply reseated by the case thrust, except in low pressure rounds which don’t produce enough thrust. This isn’t usually noticeable in rifle or pistol loads, because the primers don’t have enough room to move much in a rifle, and only in revolvers do they have the ability to so easily lock up the action.

Even with loose pockets, the case thrust of normal loads would reseat the primers. If they are left proud, it’s low pressure ammo.
 
Varminterror said:
Primer pockets don’t have to be loose to allow the primers to back out. All primers in all firearms do, they are simply reseated by the case thrust, except in low pressure rounds which don’t produce enough thrust. This isn’t usually noticeable in rifle or pistol loads, because the primers don’t have enough room to move much in a rifle, and only in revolvers do they have the ability to so easily lock up the action.

Even with loose pockets, the case thrust of normal loads would reseat the primers. If they are left proud, it’s low pressure ammo.
Click to expand...
^^^^ That Right There ^^^^
It really is as simple as that.
 
But...if the primer backed out after being fired, wouldn't the cylinder have locked up prior to bringing the next round up under the hammer.

I could see the cylinder revolve and lock in place before the hammer stopped. The shooter confirmed that he felt the bolt lock-up before the trigger stop moving
 
9mmepiphany said:
But...if the primer backed out after being fired, wouldn't the cylinder have locked up prior to bringing the next round up under the hammer.

I could see the cylinder revolve and lock in place before the hammer stopped. The shooter confirmed that he felt the bolt lock-up before the trigger stop moving
Click to expand...
If you look at the recoil shield face it's not completely machined flat, so the high primer could easily be stopping at some point around it even several shots after the offending primer remains too high. You might be able to find a witness mark or rub where this is happening and stone it down to help with the issue. Revolver manufacturers don't often machine the recoil face totally flat because there's no reason with normal ammo but in this case it could be worth a look.
 
9mmepiphany said:
But...if the primer backed out after being fired, wouldn't the cylinder have locked up prior to bringing the next round up under the hammer.
Click to expand...
No, it is immediately re-seated from the pressure of the round pushing the case back over the primer and against the breech face.
 
From the OP it was a "possibility" that the primer backed out it was not verified.

The thread title is "misleading"

I was thinking it might be a burr on the rim of the case, but wouldn't that drag all the time?
Could it be a primer backing out and what would cause it?
Anyone every encounter this previously?
Anyone have any ideas of where to start looking?
 
9mmepiphany said:
But...if the primer backed out after being fired, wouldn't the cylinder have locked up prior to bringing the next round up under the hammer.

I could see the cylinder revolve and lock in place before the hammer stopped. The shooter confirmed that he felt the bolt lock-up before the trigger stop moving
Click to expand...

You’re confusing yourself here:

The primer is seated fully before ignition. During initial ignition, the primer is pushed out of the back as pressure builds, just the same as the bullet is pushed out of the front. Once the bullet starts moving and the pressure builds substantially more, the cartridge case is thrust rearward as the bullet is pushed forward - the primer is resting against the recoil plate, nowhere to go, so the case reseats over it.

The revolver lock up timing has absolutely nothing to do with it, the hammer is down the entire time this is happening, all within milliseconds. All revolvers do this, all firearms do this. It’s just much more noticeable in revolvers due to the slack in the chamber/recoil plate/cylinder window, and it only causes a jam when low pressure ammo is used which doesn’t fully reseat the primer.
 
Size and deprime a few cases and just prime them. Put on your plugs and “fire” the empty cases. If you didn’t drill out the flash holes(like you were intending for plastic or wax bullets) the primers will be backed out.

After that exercise it will make more sense.
 
In reading these two threads in their respective environments: It’s very obvious revolver reloaders come at this problem very differently than the revolver shooters we have participating on the other thread. Same problem, two very different threads - a lot of speculation on the other thread about incredibly low likelihood problems in the mechanism (and even completely illogical suggestions), whereas the solution was hashed here within a couple posts.

Kinda sad to see so many revolver shooters unfamiliar with an incredibly common failure mode.
 
It happened to me once. It was about 50 years ago. Primer backed out on factory ammo. Had to send it in to S&W to get it fixed. We could not open the cylinder. We did not continue try to pull the trigger since it was locked up. Sent it in loaded.
 
I agree with the low pressure resulting in the primer being pushed out, but not back in.
This is factory loaded ammo, but that does not mean that there might be an occasional light load. Or the position of the gun during the course of fire, barrel up, barrel down, affecting powder forward or back, affecting the velocity/pressure of the rounds. Walkalong had a very informative thread on this a while ago.It's worth a read.

However, let me throw something out there out of the it happened to me camp. I had a couple of 38 Spcls I loaded that had slightly high primers. They of course bound up the gun, but not all the way and IIRC only in certain areas of the cylinder rotation.

So, maybe either the low pressure from a marginal weak round, powder position affecting pressure, or a burr on the face plate, or a slightly proud primer.
 
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