DZelenka Posted April 13, 2020 Report Share Posted April 13, 2020 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 Link to comment Share on other sites More sharing options...
villafuego Posted April 13, 2020 Report Share Posted April 13, 2020 Replace the FBP spring with an actual MP-40 spring and you'll not have any more problems. FBP springs seem to be a bit too stiff/strong Link to comment Share on other sites More sharing options...
DZelenka Posted April 13, 2020 Author Report Share Posted April 13, 2020 Replace the FBP spring with an actual MP-40 spring and you'll not have any more problems. FBP springs seem to be a bit too stiff/strong Wolf replacement springs work? Link to comment Share on other sites More sharing options...
DZelenka Posted April 13, 2020 Author Report Share Posted April 13, 2020 One more thing that I noticed but forgot to mention. It was impossible to pull the bolt far enough to the rear to put the bolt handle in the safety slot. Anyone have any suggestions for that? Link to comment Share on other sites More sharing options...
Grasshopper Posted April 14, 2020 Report Share Posted April 14, 2020 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 Link to comment Share on other sites More sharing options...
JayP Posted April 17, 2020 Report Share Posted April 17, 2020 when you are tired of guessing the fix, contact Bob Naess of Black River Militaria blackrivermilitaria.comhe reworked my Fbp assembly to preserve my original parts Link to comment Share on other sites More sharing options...
DZelenka Posted April 17, 2020 Author Report Share Posted April 17, 2020 when you are tired of guessing the fix, contact Bob Naess of Black River Militaria blackrivermilitaria.comhe reworked my Fbp assembly to preserve my original partsBob is pretty busy these days. I have another project he is working on. If I can do this myself, I will. Link to comment Share on other sites More sharing options...
Petroleum 1 Posted April 18, 2020 Report Share Posted April 18, 2020 Why not jut buy a real bolt and recoil assembly they come and go all the time on gun broker for not out of line money. Link to comment Share on other sites More sharing options...
DZelenka Posted April 19, 2020 Author Report Share Posted April 19, 2020 Why not jut buy a real bolt and recoil assembly they come and go all the time on gun broker for not out of line money.I have a spare, but I also have the FBP so I might as well make it work. Link to comment Share on other sites More sharing options...
Frank Iannamico Posted May 1, 2020 Report Share Posted May 1, 2020 I have used an FBP bolt in my (original) MP40 for years, no problems, my friend has a Erb tube gun, the bolt would not go the whole way in; tube ID too small. Link to comment Share on other sites More sharing options...
imageaudio Posted May 24, 2020 Report Share Posted May 24, 2020 (edited) 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 May 24, 2020 by imageaudio Link to comment Share on other sites More sharing options...
pitfighter Posted May 24, 2020 Report Share Posted May 24, 2020 Been running an FBP bolt in my 1943 MP40 for almost ten years - only ISS FF movie blanks, so perhaps a slight difference in what it has to do.But, it performs flawlessly. Just my ten cents. Link to comment Share on other sites More sharing options...
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