Just bought a 1943 Inland.  Everything looked ok upon receipt.  When I stripped it down to clean and lube I noticed the firing pin wasn't moving freely.   As I planned on doing a spring refresh,  I added a new FP to my order from Numrichs.  Got the new pin, bolt take down tool and Wolff spring refresh kit.  Put in a new extractor and ejector spring along with the new FP and a new hammer spring and recoil spring.  New FP floats just fine.  Took the rifle to the range today and the first shot of Korean Surplus got stuck in the chamber and would not extract.  Managed to get the brass out and found the primer completely pierced and standing proud.  I loaded one round of Wolf (the only other ammo I have) and it fired and ejected fine, but the primer is slightly pierced and appears somewhat flattened.  Fired one more Wolf and got the same result, so I packed it in for the day.

I was under the assumption,  perhaps erroneous, that M1 carbines were made to have most parts, like firing pins, be drop in interchangeable.  It seems that the FP is protruding too far, but I have no FP protrusion measuring tool.  Would the piercing of the primers also cause the primer on the Mil round to start coming out or is that an indication of improper headspace?

That's what I thought also.

Started looking to see if there was a firing pin gauge available, couldn't find any reference.  Maybe in the original tech manual.

I did find these numbers that might help if you can measure this small: minimum firing pin protrusion - .044 and maximum protrusion - .059

Thanks for those numbers.  Of course my calipers are dead and I can't find any batteries, so I can't even get a rough measurement.

It could also lead to an OOB detonation, there is an angel in the receiver that keeps the firing pin from moving until the bolt lugs are locked. Your bolt could be out of spec as well.

A headspace gauge or two is never a bad idea. Some bolts could be a little different, same for firing pins. Check your chamber too, the round shouldn’t be sticking in there.

USGI (don't want to use the M-spec word) parts?
If not (why not?) you don't know what your getting.

The safety bridge seems to be doing it's job.  Can't get the firing pin forward with the bolt out of battery.

Sure it's a GI bolt & bbl?  Most clone parts will fit even if they're not wholly dimensionally correct.

Field gauge is on the way.

As far as I know everything is USGI.  The replacement FP is a NOS Inland.

Barrel is a 43 Underwood.
Bolt has an A.I. stamped on the left locking lug, which indicates an Inland bolt.

What was the physical issue with the original firing pin?  Can it be reinstalled for diagnostic purposes?

The original pin would stick forward in the bolt after the hammer dropped (or I pushed it forward when out of the reciever).  It took some force to push it back in.  While I think the safety bridge might have prevented a slam fire, I was uncomfortable with that condition. I don't know why the pin did that as nothing appeared out of the ordinary. I do still have it.

Old cosmoline on the pin?

You could try another complete bolt. They can still be found new in the grease, in perfect shape. Not cheap, though.

Might be worth a pot of boiling water to see if there is and clear it.  

I would compare the old and new firing pins visually and measured.

there is a reason I buy dial six inch not battery operated digitals calipers.

Get a bolt disassembly tool and take it apart, soak in mineral spirits. Clean everything and anything in there that could be causing issues.

Do it right. Don’t just check the bolt in a pot of boiling water, stupid idea.

Done

Not following how temporary immersion in boiling water will rust a bolt.

Ultrasonic cleaner would be a better idea IMO

 This is a method used to clean muzzle loading rifles. The hot water evaporates quickly. If you want to err on the side of caution, use pressurized air on it.

Well, protrusion seems ok.  A little long maybe at .55, but within specs.  Still waiting on the headspace gauge.

ETA, maybe not.  I measured it a few more time and came up with .59-.60. Once my headspace gauge arrives I'll tear down the bolt again, check headspace and throw in the old pin to check protrusion.

Got the headspace gauge in.  Won't close on a field gauge, so I don't think headspace is the issue.  Checking the protrusion of the firing pins I'm having some trouble getting consistent readings with my caliper depth gauge. I guess I'm going to boil the pin and bolt, dry in the brass dehydrator, re-oil and grease.  I'll throw the old pin in the bolt and see if it pierces primers too.

If none of that works, I guess a trip to Fulton is in order.  Anyone used them before?

I've sent 3 Carbines to Fulton for work, their excellent IMO. Here's links to range reports on them

https://www.ar15.com/forums/armory/-/2-506869/?page=1

https://www.ar15.com/forums/armory/-/2-505279/?page=1

https://www.ar15.com/forums/armory/-/2-501867/?page=1

I've deleted the pictures of targets on these threads on my hosting site but the rifles themselves have been running great



The 3 in the middle are the rebuilds by FA (the one on the left is a FA, the right a Plainfield)

They are honest in their appraisals of any work you'll need IMO. I didn't "need" new barrels on 2 of 3 I sent them (the Blue Sky and "Howa") but had them installed for my own reasons.

Fulton is backed up right now, expect a 18 week turnaround (I ordered a Paratrooper model Carbine Oct 1st and don't expect it till February).

As to how they run, "Ol Blue" as I call the 1944 Inland runs like a scared rabbit

Range Report 1944 Inland ex Blue Sky

The 1943 has seen fewer rounds but so far so good. The Howa has seen 2000 rounds since I got it back, some issues with FTF the past couple range trips but I think that was the Choate stock I've been using (tight fit that needed some work) and I've been testing a wider range of mags and ammo through it. It hates Aquila brand ammo, loves Armscor and so far the Korean surplus is running fine through it.

I use very hot water and simple green to clean parts. The very hot water flash dries on parts. Works great.....