Off center firing pin… to the side? Problem?

582 Views 12 Replies 5 Participants Last post by azpoolguy, 3 mo ago

JoeyMac

Discussion Starter · 3 mo ago

So I’m fitting my barrel. I’m at .044 radial engagement and have about .005-.010 to go. I tossed a piece of lightly resized 10mm brass (for a snug fit) in the chamber to check to if I’m high enough yet… and while not yet high enough I saw it was quite noticeably off center left to right.

I triple checked everything about my barrel and brass. No issues found. Even with the barrel bottom lugs perfectly centered with gage pins and the hybrid barrel slot centered with shims… it’s still off center. If I had to guess, it looks .015 off center or so, to the left.

So I checked the FP hole. This appears to be the culprit. The FP channel backside is dead straight left to right, but the little hole has some angle to it. Is this a problem? Firing pins fit pretty tight in their holes (usually .001-003).

These are snug-fit gage pins:

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View down the FP channel; up is up and I added crosshairs to the apparent centers of the FP (red) and primary flash hole (blue).

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azpoolguy

· #2 · 3 mo ago

Who made the slide?

I had a Springfield Armory pistol that was off. It required a bushing to center the firing pin hole.

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Slapshot

· #3 · 3 mo ago

Probably not. The firing pin protrusion is minimal. You’re pic looks bad because the pin is so far out but in reality it’s probably not a bid deal.

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TStone

· #4 · 3 mo ago

I'm sure it's within tolerance

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wrmiller

· #5 · 3 mo ago

I do a high lockup fitment on all my 1911/2011s, resulting in a fairly low primer strike. I have never had an issue with light primer strikes.

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JoeyMac

Discussion Starter · #6 · 3 mo ago

azpoolguy said:
Who made the slide?

I had a Springfield Armory pistol that was off. It required a bushing to center the firing pin hole.

It’s a Caspian.
Wow, if that bushing center is where the original FP hole center was… that’s way off the mark.

wrmiller said:
I do a high lockup fitment on all my 1911/2011s, resulting in a fairly low primer strike. I have never had an issue with light primer strikes.

I read Caspian’s had higher than normal FP holes to offer more positive lockup (I don’t know if true). But I was planning to shoot for .050+ engagement regardless because this is a 10mm.

I actually don’t care about how “centered” my strike is. This is my first build… I just want reliable and tight. My concern is a firing pin hole not parallel to the FP channel with a tight .068 EGW FP binding in the hole. I’d rather not undersize the firing pin to avoid binding because 10mm can/will have primer flow issues if the pin is too loose.

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azpoolguy

· #7 · 3 mo ago

JoeyMac said:
It’s a Caspian.
Wow, if that bushing center is where the original FP hole center was… that’s way off the mark.

I read Caspian’s had higher than normal FP holes to offer more positive lockup (I don’t know if true). But I was planning to shoot for .050+ engagement regardless because this is a 10mm.

I actually don’t care about how “centered” my strike is. This is my first build… I just want reliable and tight. My concern is a firing pin hole not parallel to the FP channel with a tight .068 EGW FP binding in the hole. I’d rather not undersize the firing pin to avoid binding because 10mm can/will have primer flow issues if the pin is too loose.

I have found Caspian firing pin holes to be undersized from their spec. I have had to “turn down” my firing pins.

Depending on the brand if firing pin they range in size also from manufactures.

Isnt building 1911s? One quick example.

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wrmiller

· #8 · 3 mo ago

JoeyMac said:
It’s a Caspian.
Wow, if that bushing center is where the original FP hole center was… that’s way off the mark.

I read Caspian’s had higher than normal FP holes to offer more positive lockup (I don’t know if true). But I was planning to shoot for .050+ engagement regardless because this is a 10mm.

I actually don’t care about how “centered” my strike is. This is my first build… I just want reliable and tight. My concern is a firing pin hole not parallel to the FP channel with a tight .068 EGW FP binding in the hole. I’d rather not undersize the firing pin to avoid binding because 10mm can/will have primer flow issues if the pin is too loose.

TBH I don't even measure this stuff on my own 10mm builds. I fit the barrel as high as I can and buy an oversized FP that requires fitting so I can get a snug fit in the FP hole. The last one, based on a JEM frame and slide, had a perfectly centered (according to the old Mk I eyeball) aligned FP hole and channel. IIRC there was a small burr on the inside of the slide's FP hole that I cleaned up with a small ball end mill.

And the pistol runs great.

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JoeyMac

Discussion Starter · #9 · 3 mo ago (Edited)

I was 100% going to go JEM, but then found this Caspian slide for $175 and then Caspian offers long dustcovers officer frames (JEM did not). Gotta save money where I can… a non-MIM build sheet is already like $1500.

If this experience doesn’t scar me for life, I’m going to make it a point to do a JEM frame next. This new obsession is going to hurt (my wallet and fingers and elbows)… although I just got off of a nightvision kick, so it could always be worse.

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wrmiller

· #10 · 3 mo ago

If I could afford it, I'd like to build one more (only one, promise) Jem-based pistol.

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JoeyMac

Discussion Starter · #11 · 3 mo ago

Welp, I finished fitting my top lugs.

I ended up at .051 (give or take a thou) of engagement. Used playdoh to see the firing pin alignment. It measures ~.001 center and .015 left. It’ll probably be fine even for small primer 10mm.

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JoeyMac

Discussion Starter · #12 · 3 mo ago (Edited)

Update: got my EGW .068 FP in and it has a healthy amount of “drag” in this slide. It drops in smooth until the pin gets to the small hole, then I have to wiggle it around a bit to find the hole and is all drag from there. It’s not the diameter either; the FP hole gaged exactly at .070 and the FP measures .068 and dead straight. All my other 1911 firing pins drop right into their firing pin channels unrestricted (all the way) without a spring installed. Those firing pins (that fit) drag in this Caspian slide too.

I measured the friction/drag at about 13-14oz. I measure the spring force of the FP return springs in my other pistols to be 40-50oz, with essentially free-floating firing pins. I think it will ignite primers just fine, but I’m worried about it retracting the FP fast enough to prevent primer drag. A pin with~13oz of drag is about 25-30% of the FP spring return force when it’s expecting a free fitting pin to begin with.

I don’t think it’s bad enough to need bush’s… but I’m wondering if I should use a Wolff XP (+40%) or XXP (+85%) firing pin return spring and lap the tip of the pin a bit in its hole with some compound to reduce the frost ion some; working it back and forth by hand with a punch.

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azpoolguy

· #13 · 3 mo ago

JoeyMac said:
Update: got my EGW .068 FP in and it has a healthy amount of “drag” in this slide. It drops in smooth until the pin gets to the small hole, then I have to wiggle it around a bit to find the hole. All my other 1911 firing pins drop right into their firing pin channels unrestricted (all the way) without a spring installed.

it’s not the diameter either; the FP hole gages exactly at .070 and the FP measures .068 and is dead straight. It’s got to be dragging in the off center/angled firing pin hole. I measured the friction/drag at about 13-14oz.

I think it will ignite primers just fine, but I’m worried about it retracting the FP fast enough. I measure the spring force of the FP springs in most of my 1911s to be 40-50oz, with essentially free-fitting firing pins. A pin with~13oz of drag is about 25-30% of the FP spring return force.

My Springfield slide with the off-center firing pin hole, was nearly impossible to get the pin in.

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