What the heck is this? Double primer strikes?!

[Pyrex]

I sat down to reload some rounds for my 500 magnum, and I noticed a few anomalies on my primers while during my case inspection. I ran across two of these types of strikes, found it interesting, and dismissed it. As I got to thinking about what could possibly cause this, I found a few more and decided I should ask. Now, keep in mind there were 6 of these stikes out of 120 cases, so it certainly isn't happening frequently. However, any time a firing pin strikes a primer when it's that far out of time, especially on this gun, it could take your hand with it. I've been hand loading for years and I've never seen this before.



As you can see, I'm getting a double primer strike. I was trying to imagine how this could happen. Now, I load my 500 pretty stout. I bought it as an exhibition gun for the most part. Whenever I run into a friend who blows off any high powered pistol as unimpressive, I hand them my 500 with a 440gr loaded to 1650fps and humble them. The only thing I can think is it's possibly a bump fire/double fire situation. 500's are notorious for that. I had it happen the first time I fired one, but never with this pistol, and neither has anyone else that has fired it. However, The gun is frequently shot by other people not experienced with it, so it's possible during the discharge they are partially advancing the cylinder, but I wasn't aware the firing pin could make contact on a partial rotation. Anyone have some thoughts?

[Copper75]

My thought is that the firing pin is bouncing after firing and hitting the primer again in a slightly different place. I have no evidence to prove this but I know that the 500 has significant recoil so that is what leads me to this conclusion.
Copper

[Pyrex]

My thought is that the firing pin is bouncing after firing and hitting the primer again in a slightly different place. I have no evidence to prove this but I know that the 500 has significant recoil so that is what leads me to this conclusion.
Copper

Hmm... I'm trying to imagine this. For that to show off center it would have to be advancing to the next round extremely quickly. That makes sense if the gun recoiled in the shooters hand, reset the trigger, and then the reaction to tighten up caused a partial cylinder advance on the double action. All this would have to transpire during the time the firing pin is bouncing forward again, so fractions of a second. The firing pin has almost no mass though, you think it would have enough to even ding it?

[9.3X62AL]

Not sure those smaller spherical indents are firing pin strikes, but possibly ball/spherical powder granules trapped between primer and primer shield at time of firing. I've seen similar indents in case sidewalls created by unburned granules of WC-860 getting between chamber and said sidewalls on my 45-70 loads.

[Pyrex]

Not sure those smaller spherical indents are firing pin strikes, but possibly ball/spherical powder granules trapped between primer and primer shield at time of firing. I've seen similar indents in case sidewalls created by unburned granules of WC-860 getting between chamber and said sidewalls on my 45-70 loads.

These were loaded with 4227 which is an extruded powder, so I don't think that's probable, but that's interesting. How would that cause an inward indentation?

[9.3X62AL]

Granules are present outside the cartridge and are in place prior to shooting (from prior shot) on the chamber's surface. A considerable prompt to my duplexing of WC-860 with IMR-4198 as a booster charge was to eliminate these granules via more efficient combustion.

If I were to hazard a guess and assume the dimples were indeed primer strikes.......1) hammer falls and ignites primer/fires cartridge normally 2) under the considerable recoil of the caliber, the cylinder's locking bolt disengages from contact with the cylinder, allowing it free rotation after bullet is released--but trigger is still fully depressed 3) under this trigger stage, the firing pin is free to re-impact the primer, also under recoil force from original discharge 4) trigger stage also leaves advancing hand in place on cylinder ratchet, preventing reversed rotation and possibly prompting incremental forward rotation due to recoil.

Just thinking it through.

[Pyrex]

Granules are present outside the cartridge and are in place prior to shooting (from prior shot) on the chamber's surface. A considerable prompt to my duplexing of WC-860 with IMR-4198 as a booster charge was to eliminate these granules via more efficient combustion.

Interesting. I thought you were saying powder got in the cup itself earlier. The two prior cases had considerably deeper indentations. But that's certainly interesting. I do occasionally get unburnt powder, but overall it's a pretty clean burn. I will keep an eye on it.

[9.3X62AL]

We walked on each other Look at my upgraded post.

[nicholst55]

I've seen similar marks on very heavy .44 Mag cases fired in older M29 S&W revolvers. IIRC, the cylinders were actually unlocking and slipping backwards under recoil to cause those. This led to S&W's development of the M29 'Classic' model, with some minor lockwork changes which were supposed to eliminate this. It might be worth contacting S&W and asking them.

[Pyrex]

I've seen similar marks on very heavy .44 Mag cases fired in older M29 S&W revolvers. IIRC, the cylinders were actually unlocking and slipping backwards under recoil to cause those. This led to S&W's development of the M29 'Classic' model, with some minor lockwork changes which were supposed to eliminate this. It might be worth contacting S&W and asking them.

That's interesting. I do have an older Model 29 myself, I'll have to look at some of those cases and see if mine is doing that as well.

[Who's this Guy ?]

The one Hornady case looks to have a drag mark between the primer indentation and the other dimple. Something appears to be moving around to cause that. I would guess the cylinder unlocking theroy the most plausable. I do believe a call or email to S&W might help, but be prepared for them to deflect the issue to using reloads.

[w5pv]

It may be some foreign material on the primer seater.Have you checked to see that it is clean?

[44man]

S&W springs, none of you have seen my posts on them.
The cylinder stop spring is too weak and if it was weaker the cylinder will unlock and spin to another chamber and double. The cylinder stop design has inertia and needs a strong spring to hold it under recoil.
Next is hammer bounce from internal pressure on the primer, it kicks the hammer back even on a SA, weak hammer springs can let the hammer go almost full cock too.
Your gun is unlocking just enough to let the cylinder move and hammer bounce gives another strike. Cylinders on a S&W move BACKWARDS from torque.
S&W has new, stronger springs if you explain the problem.
I fixed several 29's when I had no springs by putting a tiny lock tumbler spring inside the cylinder stop spring.
Everyone, even S&W was calling it a double trigger pull with the .500 doubling, shooter error. It took a long time for them to find out I was right. As recoil increased with heavier calibers, the problem got worse.
The enhanced model 29 has the same internal parts except for springs. They also started to harden the cranes because too many guys were bending them. At one time I could bend the cranes back by hand because some jerk would flip the cylinder shut and bend it.
At one time they used a front bushing in the cylinder front. It would work loose, move forward and lock a gun or make it hard to cock. The 27 was famous for that with more recoil from the .357.

[Forrest r]

Thank you for an excellent post 44man, you nailed it!!!!!

[ole 5 hole group]

Jim - I believe you have the correct analysis. I had a 29-2 that would do the exact same thing after a couple thousand heavy loads leaving that double primer strike appearance. After a couple months of double striking, the cylinder would start rotating backwards a couple times per cylinder load, so your next pull of the trigger fell on the previously fired charge hole. Always sent it back to Smith and they would return it within a month ready for another couple thousand rounds. Several years ago they fixed it right and no problems since. Never heard of a 29 doubling from a weak cylinder stop pin before.

[Outpost75]

This illustrates both cylinder backspin and hammer bounce, which are characteristics of the S&W design in heavy recoil.

[44man]

Jim - I believe you have the correct analysis. I had a 29-2 that would do the exact same thing after a couple thousand heavy loads leaving that double primer strike appearance. After a couple months of double striking, the cylinder would start rotating backwards a couple times per cylinder load, so your next pull of the trigger fell on the previously fired charge hole. Always sent it back to Smith and they would return it within a month ready for another couple thousand rounds. Several years ago they fixed it right and no problems since. Never heard of a 29 doubling from a weak cylinder stop pin before.

True, never seen the 29 double but the click for the next shot happened with a few of them.
The .500 with the heavy cylinder and added torque can spin to the first chamber before hammer bounce stops. A gun prone to that should have the chamber under the hammer empty, then it can't double. New springs will fix it.
S&W tries to balance springs for good trigger pulls but they buy springs and never know what a batch will do.
I did a lot of part time locksmith work and have a lot of those tiny springs. Just the few ounces added by putting one inside the cylinder lock spring worked like a charm.
I save all springs from anything torn apart, have cans of them plus gunsmith springs but never found a match for the S&W spring.
By the way, the internals of the big S&W's are beautiful pieces of perfection.