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FBP Bolt and Recoil Assembly in MP40


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I bought a really great condition FBP bolt and recoil assembly from IMA to use in one of my original MP40s. I tested it on Friday and was disappointed. With PMC 115 gr ammunition, it fired and ejected fine but ran away. With S&B 124s, it didn't run away but it have frequent failures to eject. Any thoughts?

 

Dan

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Hi,

 

I have one of those bolt assemblies in my MP-40 tube gun. I just cut coils from the FBP recoil spring until it ran with the ammo I like to shoot. I did not have any trouble reaching the safety slot. It has been years since I was into the recoil assembly but I think there are 2 springs in there. The plunger on the second spring could be stuck. Remove the stake and see what is in your recoil assembly (and clean the 60 year old lube out of it :) ).

 

Just a thought,

 

Grasshopper

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when you are tired of guessing the fix, contact Bob Naess of Black River Militaria blackrivermilitaria.com

he reworked my Fbp assembly to preserve my original parts

Bob is pretty busy these days. I have another project he is working on. If I can do this myself, I will.

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  • 2 weeks later...
  • 4 weeks later...

Dan,

 

I do the exact same setup. I have a vet bring back MP40 and didn't want to risk breaking the firing pin. I've purchased 2 FBP bolts from IMA and they both run fine. I typically run Fiocchi 115 which is considered on the hot side. Sounds like you already know this and I've always considered PMC and S&B hot ammo too so I think your on the right track. Might try some Fiocchi?

 

As far as the runaway gun, this is very indicative of a bolt not cycling far enough back to catch the sear. I would think if you can run some hotter ammo through your MP40, it will solve the problem. Perhaps just keep trying other brands. It doesn't take long to use a box in a subgun and always fun to test!

 

The failure to extract is a bit of a mystery. You would think a faulty extractor or ejector but since it runs fine with the PMC, that seems to eliminate that as the culprit. Do you have the same issues when running the original MP40 bolt with firing pin? Also, you might want to case gage and measure the overall length of the cartridges your firing. Some ammo is manufactured to NATO specs and others to SAMMI specs. Ammo that doesn't spec well with your gun typically manifests itself as a failure to feed, but heck, I've seen stranger things.

 

My workflow for solving any firearm issue is to ask my wife . . . just joking . . . it's to isolate. I number my mags, change only one thing at a time, etc. And if you order a new recoil spring from Wolff, I suggest you order a package of magazine springs as well. Half my issue are solved when I have full power springs in the mags.

 

Looking forward to hearing how you solve this one.

 

Cheers! Scott C.

Edited by imageaudio
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