Primers back out & jam the cylinder

[Grouchy Spike]

   I have two new Cimmaron Open Tops, .38 Spec, Army, 7 1/2 bbls.  One has chronic problems since the third shot where the primers occasionally back out of the case slightly, become a 'high' primer, just far enough to jam the cylinder. 

All primers fired in this pistol  have a really deep indentation, nearly if not actually  piercing the primer.

I've loaded fired cases with spent primers into this Open Top that have been fired by the other Open Top that has no problems, and 'fired' these cases. The indentation into the primer caused by the firing pin strike did NOT deepen.  So my firing pin is NOT too long or striking too deeply.

The ammunition is not the problem, as I've used several different brands, and all primer strikes are deep and some primers will back out, jamming the cylinder.

I've primed empty cases and fired them with no  powder charge, and the problem continues with deep indentations and the occasional 'high' primer. 

Aha!  So the problem is not caused by the firing pin, at least initially.  And at least by eyeball, the firing pins on both pistols extend the same amount past the recoil shield when the hammer is down.

The problem appears to be that the cartridge case rebounds to the rear after firing, and loosens the primer, and there is a secondary hit of the primer on the firing pin.  Is this possible?

In the meantime I've ordered another Open Top so as to continue shooting.  And considering that I have a 50% failure rate on the first two Open Tops, I'll change that order to two Open Tops so as to be statistically assured that I'll have another Open  Top that has no problems.


Does anyone have any experience with these symptoms, and have a solution?

[Missouri Marshal]

Backed out primers are often caused by light loads.

[Grouchy Spike]

Backed out primers are often caused by light loads.

Didn't know about that, but these aren't light loads. 

They are factory cowboy loads including Magtech with 125 gr and 147 gr bullets.  When the cases were fired without powder, with primer only, the primers exhibited the same behavior as with factory loads.  I guess one could say that these are light loads since there is no powder in them. 

But I'll run some primer-only cases through the other Open Top to see what happens there. 

And I'd wonder why the problem appears only on one of the two pistols with the same ammo.

I'll run a feeler gauge between the cylinder and the recoil shield to determine in that clearance is reasonably similar between the pistols

[Grouchy Spike]

I've checked the diameter of the firing pin hole in the frame on both Open Tops - between 3/32 and 5/64 inch on both.  Don't have a drill bit between these sizes.

[Flint]

Firing a primer only in a case will tell you nothing, because a primer only empty case will guarantee the primer backing out.  Shooters who shoot wax bullets with no powder have to open up the flash hole to prevent primer backout, then make sure they don't use those cases for anything else.

As mentioned, too light a load can back primers out.  I consider 125 gr too light for Cowboy level load, usually that light a bullet is used for high velocity +P loads.  a 148 to 158 gr bullet will perform better internal ballistics.

I would venture excessive headspace, and the case is sticking to the chamber enough to allow the primer to be blown back and not reseat.   Primers ALWAYS back out when fired, normally the case recoils into the breech face to reseat it.  Yours don't seem to be recoiling, or recoiling hard enough to do the job.  Are the chambers too rough?

The proper position for the Open top wedge is with the head of the retaining screw just up against the inner face of the clearance cut on the wedge.  Drive the wedge in until the screw will turn against the barrel to lock it, then gently drive it back out until the inside face of the screwhead is against the clearance cut.

That wedge position is where the headspace and cylinder gas ring to barrel clearance should be correct.  The cylinder gap is set by the length of the gas ring, which is the cylinder gap longer than the barrel extension.

I found the Opentop firing pin to be too long, and too sharp.  Taking an Arkansas stone to the firing pin nose and blunting it and shortening it a bit will help, and prevent piercing.  I do not understand why Uberti made such a sharply pointed firing pin.

John Browning actually designed a Machine gun before WWI that used the primer backout to unlock and cycle the action.

[Grouchy Spike]

Thanks for your reply. You and Missouri Marshal have smartened me up. 

Headspace on both Open Tops is about the same, within a couple of thousandths.

The chambers so seem rough because some cases must be hit firmly with the ejector rod to be ejected.  I'll smooth them with Brownells chamber hone.  The rough chambers match the out of round mandrell where the wedge slot was milled, and the excessively tight wedge.  This must have been a Monday or Friday revolver.

Ill blunt the firing pin, shorten it slightly, and order a replacement from Smith Shop.

And if this doesn't solve the problem  I'll use the 147 gr loads.

Thanks again.

[Linn county ranger]

Hello Grouchy,

I have 2 friend that I shoot with that have had the same problem. There was a good thread on the SASS wire back in November about it as well.
What people have found out is that some of the open tops recoil shields are  soft and it is not letting the primer go all the way back in the case after firing. There are some smiths that are putting hardened bushing in the frame like a singl action army. I think someone on theer said to send it back to Cimmeron and they would fix it.

Hope this helps

[Grouchy Spike]

Thanks for your post.  Looked at that thread. 

Several cowpokes (and a local retired gunsmith) have said that the likely cause of the problem is that the cartridge case doesn't grip the walls of the chamber sufficiently during detonation, and the case moves to the rear, slams the primer to the rear.  That is likely the cause, as since I honed the chambers of both cylinders, both OTs now have the same problem.  Heavier loads reduced the problem, unfortunately added to recoil.  So the solution  appears to be roughing up the walls of the chambers.  How to roughen them up is another question to which I don't have the answer yet.

Turnaround time at Cimmaron is 60 - 90 days when I inquired.  I can't delay gratification that long!  Must find a local solution.

I've fired the same loads during last Saturday's match, in a pair of new out-of-the box Cimmaron OTs.  They don't have the problem, but one OT does show deep penetration of the primer.  Dont' know if it's the firing pin causing that upon initial contact, or the case moving to the rear and providing a second contact with the firiing pin.  In any event, I ain't touching the chambers!

I've ordered replacement firing pins from Smith Shop for all four.

These OTs are a hoot to shoot tho!  Nicely balanced, good feel.

[Fox Creek Kid]

Sir, this is inevitable with light  loads. All revolver cartridges will slide back upon detonation. It's called physics. The primer is pressed back into the case when the rear of the case hits the breech face. Revolvers have to have headspace in order for the cylinder to turn. You simply need a heavier load to solve your problem. This would happen in a Ruger Redhawk with light  loads.

Content edited by Deputy Marshal Rawhide Rio

[RRio]

Let's keep it friendy, boys.

[Grouchy Spike]

Sir, this is inevitable with light  loads. All revolver cartridges will slide back upon detonation. It's called physics. The primer is pressed back into the case when the rear of the case hits the breech face. Revolvers have to have headspace in order for the cylinder to turn. You simply need a heavier load to solve your problem. This would happen in a Ruger Redhawk with light  loads.

Content edited by Deputy Marshal Rawhide Rio

Thanks for your interest Fox Creek!  And your comments. 

These .38 Special loads are about 750 fps, max 800 fps.  All factory new or remanufactured.  And all loads have been shot in four Vaqueros, two Uberti Cattllemen, and two other brand new Uberti Open Tops.  All of these eight revolvers have no difficulty with these loads.  None whatsoever.

So somewhere in these two six guns is the problem. It's something with the first one of the OTs (#37) new out-of-the-box, and then after I honed the chambers in both, it's common to both of these two OTs (#36 too).

I measured the headspace between the recoil shield and the rear of the cylinder with the hammer cocked on all four OTs.  It's 0.063 on #37; 0.071 on #36; 0.69 on #27; and 0.63 on #28. 

#36 has some fore & aft play not found on the other three that allows headspace to increase to 0.079.  The other three OTs lock up tight.  #36 was shooting OK with this headspace variation before I honed the chambers.

Any ideas?  Otherwise I'll send it to a cowboy gunsmith for diagnosis, and while it's there let him tune it up, smooth it out.

[Fox Creek Kid]

G.S., I answered your PM with a PM.