Strange primer strike

[curioushooter]

See picture. These are 44 SPL+P loads.

262556

Load with the extra little dent was 12.5 grains of Blue Dot pushing a 240 grain MP-429244 small HP pin. This load should be less than 12.5 grains of BD as a standard weight (255 grain) 429244 is 12.5 grains of BD. Velocity 1225 FPS from my S&W 624 6.5."

Normal load is 8.5 grains of Unique pushing the same bullet for 1090 FPS in the same revolver.

I've noticed this before with heavy charges of 2400 with both the 429215 and 429421. It seems to be recoil related as the pressures of the 8.5 grain Unique load and the 12.5 grain BD load are withing a couple thousand PSI probably.

No measurable difference in case web expansion.

Anybody have an idea of what is going on? The revolver has two changes I've made from factory configuration. It has a Pachmayr presentation grip and I put in a Wolff Type I hammerspring which should run at factory weight and a reduced return spring. 624s were made in '84 and '85 I think. They have a regular type of firing pin attached to the hammer. They hammer on a 624 is odd...it is not case colored like other stainless guns. It is a stainless part as well and it is the target style so it is a heavy hammer. I thought this may be related to bounce. Endshake is ~.004.

[onelight]

Is that one strike from the FP . It looks like it was was hit with the cylinder / crane not fully locked in place but that can't happen on any Smith I have ever handled .
My mod 29 developed excessive end play and the cylinder would unlock during recoil but always locked up prior to firing.
I have no idea strange looking situation.

[megasupermagnum]

.004" end shake is not horrible, but S&W is not very tolerant. A .003" shim may be a good thing. The other thing is the cylinder stop or bolt has a weak spring. Every S&W 44 or 41 magnum I ever tried had the problem, mostly if you don't have a very strong two hand grip on the gun. Your loads are up nearing 44 magnum territory. Wolff sells an extra power spring that seems to have worked in mine.

[edp2k]

It looks like, after firing, the cylinder unlocked and indexed a bit and the hammer bounced and hit the primer
a 2nd time, making the 2nd smaller fp indent.
I can't see any other explanation.

I agree about getting a stronger cylinder stop/bolt spring. Try wolf www.gunsprings.com

[curioushooter]

I will get that cylinders stop/bolt spring. It makes some sense and in a way 624s recoil worse than a 629 because they have a much thinner barrel and weigh about a half pound less (6.5" barrels). These loads are approaching low end-44 mag territory and it is true that the loads using Unique or standard loads at 44 special power never do this. Only 2400 and Blue Dot loads have done this. It could be a weak spring letting the cylinder go and then the hammer bounces again on the primer before the return spring resets the action and moves the hammer block into place.

Might as well pick up some endshake bearings while I am at it with the bolt stop spring.

[EMC45]

Looks like hammer bounce

[alfadan]

It must be the new spring. Any idea what the headspace is? I think the fired case is blowing back, hitting the firing pin causing hammer bounce.

[onelight]

Good information cylinder shims stopped the unlocking on my mod.29 but it looks like I should replace the bolt spring I don't know why , only been shooting it 40 years :D
I hope the shims and springs cure yours.

[Silver Jack Hammer]

I had some hammer bounce with my .44 Special Colt’s SAA and I am not seeing the same strange primer marks

[Baltimoreed]

I can’t imagine that the cylinder is unlocking but I’m wondering how much play your cylinder and crane has. I couldn’t imagine the frame is flexing either. Back off your loads to see if it stops or replace the original spring one at a time to see what happens.

[onelight]

The unlocking we are talking about is from the bolt not the crane, it makes sense to me if excessive end shake allowing the cylinder to unlock from the bolt and turn under recoil combined with hammer bounce That could leave the second mark on the primer.

[megasupermagnum]

I never gave it much thought, but my guess is all hammers bounce. I would consider that normal. The video below is of a 22 lr. I think the only problem with this 624 is the cylinder unlocking, which is a well known problem with heavy kicking S&W's.

https://www.youtube.com/watch?v=RynFnKzt9JM

[Silver Jack Hammer]

I had a 1962 N frame Smith, S serial number .44 Mag, it spit shaved lead with medium range loads. When I visually inspected it I could not figure out the cause. I believed the cylinder was unlocking. I sold it to man who would treat it better than I intended to.

My 3rd generation Colt’s SAA .44 was hammer bouncing to the point it would catch on the safety notch occasionally. The loads were warm. I checked and verified I did not have a light SASS mainspring in it.

[Baltimoreed]

Try this experiment then. Get a sharpie and mark your brass at 12:00 and make sure it stays at 12:00 when fired to see which direction your cylinder is moving, L or R. Might give you another clue to solve your mystery. I have a couple of N frames in 45acp but never seen this trick.

[onelight]

The bolt cuts in the cylinder and the bolt are both round just the right shape to cam the bolt out of the cylinder with excessive end play combined with a weak bolt spring. At least that appears feasible to me . And it matches the experience I had with my 29 I could fire a round (full power only ) and then manually turn the cylinder with the hammer down and hear the bolt click back into place. But I did not have the hammer bounce deal going on that left a mark on the primer.

[osteodoc08]

It looks like, after firing, the cylinder unlocked and indexed a bit and the hammer bounced and hit the primer
a 2nd time, making the 2nd smaller fp indent.
I can't see any other explanation.

I agree about getting a stronger cylinder stop/bolt spring. Try wolf www.gunsprings.com

Had the same thing happen on a 29-1. Looked exactly the same. Realized my love affair with the 41 was alive and well and it went down the road