Off-center firing pin strikes

[cascadecoyotekiller]

Hey everyone, I just finished putting together a rifle chambered in 300 WSM using a Zermatt Origin short action, and while checking for pressure signs on the first 20 rounds through the gun noticed that my firing pin strikes are about 10 thousands off of center. I called Zermatt and won't be able to speak to a tech guy until next week, so I figured I'd see what you gentleman had to say.

 

[quigley257]

It's more likely that your brass has the primer pockets drilled off center than the bolt being out of spec.

 

[Winkfish]

I have an Origin and TL-3 that are both like that. I have no less than 5K rounds on each of those actions and I have never had an ignition or accuracy issue with them. I have had 6ARC, 6 Creed, 6.5 creed, .223, and 7mm-08 barrels on them. The barrels have been Brux, Bartline, Proof and Rock Creek. This is also across brass from Alpha, Lapua, Hornady, Starline, Nosler, Peterson, and ADG.

I was told it shouldn't be an issue and I have not see it produce any accuracy issue. Unless you are seeing something odd on your primers, it would not raise concerns to me based solely on my personal experience.

 

[Radman]

Hey everyone, I just finished putting together a rifle chambered in 300 WSM using a Zermatt Origin short action, and while checking for pressure signs on the first 20 rounds through the gun noticed that my firing pin strikes are about 10 thousands off of center. I called Zermatt and won't be able to speak to a tech guy until next week, so I figured I'd see what you gentleman had to say.

The only ones I have that do this are semiautos.
Though I hate to see this I cannot say with surety that it affects accuracy at all, (although it is one of the 1st things that I check on a new firearm ). IF it's a shooter I would ignore it.

 

[cascadecoyotekiller]

It's more likely that your brass has the primer pockets drilled off center than the bolt being out of spec.

I just checked a few pieces and they are all within 1 thousandth.

 

[cascadecoyotekiller]

I have an Origin and TL-3 that are both like that. I have no less than 5K rounds on each of those actions and I have never had an ignition or accuracy issue with them. I have had 6ARC, 6 Creed, 6.5 creed, .223, and 7mm-08 barrels on them. The barrels have been Brux, Bartline, Proof and Rock Creek. This is also across brass from Alpha, Lapua, Hornady, Starline, Nosler, Peterson, and ADG.

I was told it shouldn't be an issue and I have not see it produce any accuracy issue. Unless you are seeing something odd on your primers, it would not raise concerns to me based solely on my personal experience.

Thanks for the reply. That's good to know that you are seeing it on multiple different chamberings. I trust my gunsmith but was thinking there was a slight chance that the chambering was off center. I wonder if it has something to do with the design of the controlled round feed and floating bolt head. Since you've got a few of these actions I have another question for you. The magnum bolt head grips the base of a piece of magnum brass well enough that a round will easily stay on it if you snap one into there with the bolt out of the gun, but I also have a standard bolt head and noticed that a standard piece of brass is pretty sloppy when you snap a round onto it, to the point that it will pretty easily fall out of the bolt head. Any thoughts on why that might be?

 

[Winkfish]

I have all 4 bolt heads sitting around, I can take a picture of them with various cases. I do have the magnum head as well. I am tied up from now till Sunday night so I will get you some example and images then.

Regardless, I have not had any feeding issues with any of my cases from a magazine or just placing a round in the chamber and closing the bolt.

Just another data point for you, I have tried the Timney 210, and HIT. From Triggertech, the special, primary, and Diamond triggers with the TL-3 and Origin. All work great depending upon application.

 

[memtb]

I don't have any "high end" custom rifles…..but if memory serves me well, most hit off-center. 0.010" doesn't seem to be a great deal off-center……at least to me!

Heck, most of my bolt firing pin holes have several thousandths, probably 3 to 5, larger than the firing pin. memtb

 

[cascadecoyotekiller]

I have all 4 bolt heads sitting around, I can take a picture of them with various cases. I do have the magnum head as well. I am tied up from now till Sunday night so I will get you some example and images then.

Regardless, I have not had any feeding issues with any of my cases from a magazine or just placing a round in the chamber and closing the bolt.

Just another data point for you, I have tried the Timney 210, and HIT. From Triggertech, the special, primary, and Diamond triggers with the TL-3 and Origin. All work great depending upon application.

I really appreciate that, thank you.

 

[cascadecoyotekiller]

I don't have any "high end" custom rifles…..but if memory serves me well, most hit off-center. 0.010" doesn't seem to be a great deal off-center……at least to me!

Heck, most of my bolt firing pin holes have several thousandths, probably 3 to 5, larger than the firing pin. memtb

It's not a lot, but it's enough to see with the naked eye, especially if you roll the brass along a flat surface. I'm not losing any sleep over it, but this is my first high end action and since none of my factory rifles do this I was curious. It's also my first controlled round feed versus push feed and I thought there's a chance that it had something to do with that.

 

[MagnumManiac]

Do you understand how the firing pin indent is formed?
Being off-centre AFTER firing is NOT the indicator that anything is off-centre, it is the movement in the firing pin and which way it settles as the case is slammed into it changing the look of the indent and it's position. Some action types cause this excessively due to 2 things, plunger ejector spring strength and, amount of clearance between firing pin assembly inside the bolt and firing pin clearance.
The initial strike may just be centred perfectly, but the subsequent pressure drives the case off-centre or the firing pin off-centre.
Have seen so many rifles from customers that believed the rifle was eccentric due to this off-centre firing pin indent, but shown on the lathe spinning, there was no eccentric condition anywhere…

Cheers.

 

[cascadecoyotekiller]

Do you understand how the firing pin indent is formed?
Being off-centre AFTER firing is NOT the indicator that anything is off-centre, it is the movement in the firing pin and which way it settles as the case is slammed into it changing the look of the indent and it's position. Some action types cause this excessively due to 2 things, plunger ejector spring strength and, amount of clearance between firing pin assembly inside the bolt and firing pin clearance.
The initial strike may just be centred perfectly, but the subsequent pressure drives the case off-centre or the firing pin off-centre.
Have seen so many rifles from customers that believed the rifle was eccentric due to this off-centre firing pin indent, but shown on the lathe spinning, there was no eccentric condition anywhere…

Cheers.

Pulling the trigger on a piece of primed brass with no powder or bullet would eliminate any pressure back into the bolt face, correct? I tried this when I got back from the range that night and it was consistent with everything that I had shot earlier.

 

[MagnumManiac]

Pulling the trigger on a piece of primed brass with no powder or bullet would eliminate any pressure back into the bolt face, correct? I tried this when I got back from the range that night and it was consistent with everything that I had shot earlier.

Well yes and no. You stated it appears .001" off-centre, this may be true, or it may be what it appears due to pressure pushing it one way in the body. All firing pins move in the body, if it moves to one side consistently, then there is a force pushing it that way, if it was consistently all over the place, then it is from too much clearance. If you draw a line across the case head and align it the same way each time you chamber a round, this will tel you a lot about what's going on.
Remington had a huge problem with 2 things, the firing pin spring would go into an 'S' shape when cocked, this would force the assembly off-centre and drag inside the bolt causing a harmonic disruption, often causing bent firing pins, the other problem was that the entire bolt was being forced in the opposite direction of the plunger ejector causing a crooked bolt condition, which was evidenced by off-centre primer strikes. It took us some time and effort figuring that one out. New springs in both rectified the problem.
Have you had the bolt apart?
I have found swarf and other objects inside brand new bolt bodies on several occasions, even broken firing pin springs, retaining pins protruding and poorly machined holes with huge burrs on the edges.
All of this can and does cause alignment issues, even bending firing pins…

Cheers.

 

[Winkfish]

Here is an image of a 6 ARC case:

Here is a magnum case:

Here is a 308 based case:

Here is one of the bolt heads with close to 7K rounds on it:

The all fit in there fairly snug when out of the chamber. As noted there is a little movement, however very minimal.

Is there anything else you would like to see?