Do NHM 91 bolt, firing pins and/or carriers have a reputation for soft steel?

I recently bought a lightly used NHM 91.  I took it shooting today and couldn't get through a magazine without several fail to fires.  I'd say that every 3rd round or so failed to fire.

I also brought a Century Yugo M70AB2.  I bought this also used but in good shape.  I had no FTF's with the Yugo.  

I compared the fired Yugo brass to the NHM 91.  To my eye, the Yugo firing pin strikes are deeper than the NHM 91.  The light primer strikes below are on rounds that did not fire.  

The ammunition was Wolf but I also had some Golden Tiger and had the same problem with light primer strikes with the NHM 91.

I am also posting this in the general AK section, but I am trying to determine if the NHM 91 is known for soft firing pins, bolts and/or carriers, so hopefully the mods don't delete it.

I did find this in a search for my problem.  I'm simply copy/pasting it and don't know if this is generally true or not:  Link



In this thread, I would like to know if this is a known problem with NHM 91's?

Yugo left, NHM 91 middle, and the right is a Golden Tiger round likely with only the firing pin mark from chambering it:



Yugo on the left, the other 3 are NHM 91:



Yugo bolt face left, NHM 91 bold face right:

The profile on your NHM's FP looks much squarer (hits with more surface area) than your Yugos. Try a new FP, RPK types(that are fluted work nicely), or carefully taper the edges of your original by carefully stoning it. Don't make it pointy or shorten it,  you'll pierce the primers or it may not fire at all.
Try swapping the FP from your Yugo to the NHM first and see if it works first. Also check your hammer spring.

As for metal hardness, unless your seeing any deformation, it should be fine.

I will look into the hammer spring possibility as well.  I think changing the firing pin out and maybe the spring are both good ideas, but possibly changing out the hammer, bolt and firing pin is something to think about.

Update:

I got more pictures.  I dug through my parts bin and came up with two other AK bolts.  One uses a free-floating firing pin and the other has a spring-loaded firing pin.  I wanted to get an idea about the total length of the bolt to see if the NHM-91 was shorter or not.  I also wanted to see if the firing pin was not only "flattened" but also shorter than it should be.  I also took a picture of the NHM-91 hammer.

Polytech bolt with free-floating firing pin, Left
NHM-91 bolt, middle
Spring-loaded Chinese AK bolt, right



Rear of those same bolts showing what I think is a shortened NHM-91 bolt.  You can also see that the NHM-91 bold is more "cone" shaped.  If you ignore the part of the spring-loaded firing pin that is protruding on the bolt on the right, then the right bolt and left bolt appear almost identical in length.



Rear of bolts in same order:



Front of bolt face. Polytech free-floating firing pin on left, NHM-91 on right.



Side view of front of bolt face.  Polytech free-floating firing pin on left, NHM-91 on right.  To me, it appears that the NHM-91 firing pin is not only "flattened", but it doesn't protrude as far as the Polytech bolt which could explain the FTF's.



"Stepped" hammer of NHM-91:



I'm really wondering if there is any way to replace the bolt with a standard length one, make sure it headspaces properly, and use a regular hammer.

I know very little about AK's so your theory certainly seems valid.  I'm having someone else take a look at this in person to see what direction to go, but I think you're exactly on the right track about replacement.

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Wow, never would have thought the NHM bolt would be shorter than standard Chinese bolts.Does the stepped hammer strike the FP squarely? I had an NHM that had a similar issue but it was sporadic -- only once or twice a range session. Was the NHM converted with US trigger parts or are they OEM? If the rifle has a low round count, you might try re-profiling the hammer face.

Good post. Keep us posted.

I'll check on the hammer.  It's hitting but I think the issue is in part the shortened firing pin which doesn't penetrate the primer enough.  It's supposedly all OEM parts.  I only have what I've read on the Internet, but the changes such as shortening of the bolt and firing pin as well as changing the hammer profile were all done in China/OEM.

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I have already contacted an AK gunsmith to fix this.  I'm not touching this since it will need to have the headspace checked.  In the end, the changes you posted will have to happen.  There's just no other way around it.  There's no way to replace the firing pin as it would have to be heat-treated after cutting it anyway which would be a recipe for it to fail again.

ETA:  I actually already have all the parts that would be needed anyway.

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Update:  03/18/2016

I got my rifle back from the gunsmith.  I sent him both spare Chinese bolts I had and the one with the spring-loaded firing pin head-spaced perfectly.  He said it was even better than the one with the short bolt!

He replaced the FCG as well and it test fired well.

I'm going to take it out to the range this weekend and hopefully everything goes well.

Not sure what to do with the spare bold.  Probably the only thing I can use it for is a spare extractor.

I buy stuff off the EE every now and had the two spare bolts I had gotten over the years.  Chinese bolts are very expensive at Polytech's website.  A stripped bolt is $155!  So I'm very glad one of the ones I had head-spaced correctly.  I also have some spare spring-loaded firing pins I bought a while back.
 

I had this problem with my 56S-2

Kept getting random FTF with primer hits like yours.Maybe 1-2 out of a 30 round mag.

Put in a free float flat firing pin and tossed the spring loaded firing pin.Also changed out the disconnector spring in the sear which had a kink in the spring.

Fixed it right up.You dont have to use the spring on the spring loaded firing pins.You can remove the spring and reinstall it free floated or replace with a regular AK pin.

I did not know that.  Thanks!

Still have to put it through its paces so hopefully that goes well.

Let us know how it does with at least 3-4 mags through it

It sounds like you may have it fixed, but have you thought about disassembling the original bolt and making sure the firing pin channel was clean and free of any burrs as well as inspecting the firing pin for any kind of hidden deformation?
I had an sks (free floating fp also) give me the same fits once. It ended up having some grit near the firing pin hole inside of the bolt.

I know that definitely can be an issue sometimes, especially with SKS's, but mine shook freely inside the bold.  The gunsmith also didn't find anything wrong either other than the bolt being short.

I took the rifle out last weekend and fired full:

1) Hungarian 20 round magazine

2) Russian 30 round Bakelite magazine

3) Bulgarian 40 round Circle 10 waffle magazine

The magazines all seated nicely.  I didn't have a single failure of any kind in the 90 rounds I fired.  The primer indentations were deep and sharp.  Again, I am lucky that one of the two spare Chinese AK bolts I had headspaced perfectly.

Great news,now go warm up that barrel

Indeed.  I have Chinese rear-loading and Romanian top-loading drums.

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