My thoughts on firing pin length and ignition

[Randy Lee]

Greetings all,

It has been a while since I have posted, so please forgive my intrusion... many have no idea who I am but I believe I have some experience in the realm of the current model Smith and Wesson revolvers.

I have had several people call or email asking about our firing pins and issues relating to reliable ignition in both centerfire and rimfire revolvers, so I thought I would post my observations and what has worked for me.

First let me state that the mechanics of ignition are VERY different when comparing rimfire rounds to centerfire revolvers. I will address the rimfire revolver first- in particular the 617.

Will an extended firing pin of any manufacture help ignition at lower trigger pull weights on a rimfire? Probably not.

The problem is that priming mixture has to be crushed between the fore and aft surfaces of the case rim. The brass alloy and thickness can have a substantial effect here. We also have the problem of air pockets or voids where the priming mixture may not be uniformly distributed around the case interior. So, the firing pin impression or footprint must cover a large enough surface area to ensure that SOME of the mixture gets crushed. Too large of a surface area, and the priming compound will not be crushed, just sandwiched between the rim surfaces.

In my tests, there was no net gain or improvement at lighter mainspring settings when switching between longer or factory length pins. There is also a much greater chance that a chamber will sustain damaged by the accidental dry fire... So in this case I cannot recommend using my or anyone elses extended pins.

I have had more satisfactory results by using a heavier target hammer in the rimfire revolvers. This is opposite of what I do with my ceterfire action work. To that end, I am currently working on a drop in trigger pull reduction kit for the current model 617. The kit will contain an extra mass hammer to achieve the results I desire. A more advanced version will make it's debut at this year's Steel Challenge in Piru CA.

Centerfire revolvers:

Many of my customers are law enforcement who carry J frames as off duty/backup. Many LEOs have complained about misfires with their duty ammunition in new, out of the box guns. This for me is of serious concern as I am sure it is for them. The factory supplied pins in these instances measured .483-.486 in length. In these instances, replacing the shorter pins with ones measuring .494 or greater solved the problems. My XP firing pin measures .500 and is intended for general purpose applications(current J,K,L & N frames) such as personal defense/carry or where moderate to no action work has been done to the gun. If your pin measures at least .494 there is no need to replace it.

About competition action work and firing pins:

What I have learned is that all things being equal ( minimal endshake, acceptable headspacing and chambers that aren't over chamfered for the sake of speed reloads), the length of a pin measuring .494-.496 is the optimal length when running trigger pulls in the 4-5 lb DA range. Of greater importance than overall length is the free run distance- or the distance the firing pin travels before it hits the primer.

By increasing the free run length I have been able to run sub 4 lb trigger pulls. Granted, there is much more to achieving a reliable ultra light trigger than just a firing pin. But the pin factor was the final component I needed to prove that a 3.0 lb trigger pull is doable.
At this years International Revolver Championship, Lisa Farrell ran this gun with ZERO malfunctions. With any luck, the Shooting USA episode will air with a brief segment on this gun. My only error in judgement was giving the gun 2 weeks before the big match (sorry Lisa).

In the competition circuit, the singlemost common cause of light strikes has been inadequate primer seating depth. In order to run the absurdly light triggers we do, the legs of the primer anvil MUST be firmly bedded against the primer pocket. If you speak to any of the top level competitors, they will tell you the same. I load on a Dillon 650 and my primers run .008-.010 below flush. This means that if you run your thumb across the back of the cartridge, you will feel a marked "dip" when you come to the primer. I believe most reloading manuals address this point.

With the centerfire revolver, a lighter hammer absolutely allows you to run a lighter trigger pull.

More to follow...

 

[Wayne M]

Great post, Randy. This should be put up top permantely.

 

[TSQUARED]

Randy,
Thanks for your insightful explanation.
Tony

 

[judge]

Excellent information Randy - we really appreciate it. As you know, those who shoot competition are always looking for a little "edge". Exrtended testing is the only way to be sure of the results. Good job.

 

[lobosolo]

Randy
Thanks for the info r/e fireing pins but how do you get the 650 to seat primers that deep? When I was not successful with my 650 I had to start loading my match ammo on my old star that has an adjustable primer seat.
Thanks
Jim Webb

 

[Lynyrd Skynyrd]

Cleaning the primer pockets is worthwhile too especially if they've had a few reloads.

 

[Randy Lee]

Thanks guys,

I will try to keep people updated on what I learn as time goes on.

Jim, all 3 of my 650s seem to have enough range to fully seat the primers. As long as the vertical floating of the shellplate is kept to a minimum and enough pressure is applied to the handle primers should fully seat. For match ammo, I also rotate the case and reseat again. I have found that on modern progressive reloaders such as the 650, the seating of the primer causes the shellplate and therefore the case to tilt towards the center of the plate. This means that one side of the anvil may make a firm seat in the case, but the other side is not. I can feel a slight "give" when I rotate the case and reseat. This may slow down the process, however I would rather lose time at the reloader than on a field course.
In the event that you have a short seating stem from Dillon, you could contact them and see if they have any longer ones.

For what it's worth, I now have a firing pin specifically for light action competition guns using Federal primers. They have a greater free run length and are .495. Yes, a shameless self indulgent plug...

Randy

 

[bountyhunter]

Pretty much what I found as well. As long as the length is "enough", increasing the length beyond that does nothing. As for free run length, that can be increased by relieving the front edge of the "notch" that the frame pin goes through. I had to do that anyway on some "extended" pins I bought which stuck through the breech face far enough to drag on the ammo when fully back. Theoretically, you could shave that edge more and let the pin go farther back but it might require shaving the rear surface of the pin as well.

I never did any experiments on this, but moving it back and reducing the FP mass probably would give more strike energy as it allows the pin to get a little more velocity before it hits the primer. Would be interesting to see if there is more to be gained.

 

[lobosolo]

Thanks again Randy
I have not tried the extra step with my 650 but I will. I have one of your hammers,and firing pins and I will say they do as advertised. By the way Dillon tells me their seating pins are one length only.
Thanks again for taking the time reply.
Jim Webb

 

[Randy Lee]

Hi Jim,

You are welcome. I am not sure what the manufacturing tolerances are for the primer seating rams from Dillon, but I have seen several samples of reloads from customers where the primers have been crushed onto the pocket to the point of deformation.

You can test the max travel of your priming ram by placing a primed case in that position and pressing forward on the handle until it stops. Note the position of the handle relative to the reloader's frame. I used the plastic akro-bin on the strongmount. With the handle pressed forward, I simply slid the bin until it contacted the handle. Then remove the case and press forward on the handle again. It should move considerable farther forward and push the bin towards the rear. Mine show quite a bit of travel.

One point of consideration is that when dry firing, the factory pin's forward travel is limited by the retaining cross pin that rests in the frame. The rear ledge of the cutout(in the firing pin) must stop the pin's forward travel. If the firing pin travel is not limited in this fashion, damage will likely occur:

-Fracture of the firing pin
-Breakage of the firing pin return spring
-dislodging of the firing pin bushing from the frame

Firing pin travel is usually limited by striking a primer. Under dry firing conditions, a pin that has too long of a retaining pin cut will fully compress the return spring and bind the coils. Eventially one of the three events listed above will likely occur.

The rear impact surface of a firing pin must also be considered. A domed surface is not, I repeat NOT recommended. If the gun is shot a lot with major power factor or hot magnum ammo - the back face of a hardened firing pin can over time break through the case hardened surface of the hammer. I have seen more than one instance where this has occured. Whenever the gun is fired, the rearward recoiling force of the cartridge slams the case against the breech face. Since the firing pin is embedded into the primer at this point, some force is transmitted thru the pin to the hammer which it is in contact with. This may be why the factory pins have a flat impact surface- to spread the forces over a larger suface of the hammer.