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FBP bolt and recoil disassembly question


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Been running tests with my MP40 and read on this form a post which advised to change out the springs in the FBP recoil assembly with MP40 springs. I can purchase these springs from Wolff

 

https://www.gunsprings.com/MP38%20&%2040%20GERMAN/cID2/mID130/dID349

 

But I can't find directions anywhere for disassembling the FBP recoil assembly. I'm guessing I unscrew the face of the assembly that is inserted into the back of the bolt? This part appears to be staked?

 

Can anyone provide a little direction prior to me attempting to break it open?

FBP recoil assy face 2.jpg

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Interestingly, if you examine the assembly closely, it appears that it has been staked previously? My guess is based on the other two dents in the assembly that are exactly 180 degrees separated as appears in the attached picture. I bought this FBP bolt from IMA but it definately appears to have been used.

 

Especially in comparison to a much better quality FBP system I own. The recently purchased IMA assy is on the top of the picture, the higher quality I already owned is on the bottom. The recent assy purchased from IMA is very loose as can be seen by the way the sections are somewhat crooked. I'm afraid if I ran this in my gun, it may get caught in a bind during cycling.

 

Any way to tighten up the sections or is it just too worn out?

 

 

 

 

 

Previous Stake?.jpg

FBP bolt comparision 2.jpg

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First, are you having some symptoms that indicate that the recoil spring in the assembly needs to be replaced? If the assembly functions properly there is no reason to change the springs.

Staking is really only overcome by torque which will shear the stake and. new stake will be needed when reassembled.

The telescoping sections that are “loose” will not bind when assembled in the receiver assuming that the rear end with the centering boss on the end of the rear section is secure in the hole to align it in the end cap inside of the receiver. The sections generally are self aligning but if the rear section is not secured and aligned in the hole, the bolt will not fully retract. HTH

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The purpose in changing the springs is so that I can easily reload inexpensive ammo to run in the gun. I already reload 9mm in a minor power factor (approx 135) and it would be very convenient to be able to run this softer ammo in the mp40 since I can reload it for around 11 cents a round. Plus, I load on a Dillon 1050 so can easily make 1000+ rounds an hour without breaking a sweat.

 

I currently have 3 bolt/recoil systems. One is the MP40 original matching to the gun with firing pin, etc. which I don't want to risk breaking. However, this original system will run almost any ammo I put in it including my 135 pf loads.

The other two are FBP bolt/recoil assemblies and the springs are noticably stiffer. When running the FBP system, I have to use pretty hot ammo to cycle the gun properly. Otherwise, I'm having mag dumps.

 

So, I'm assuming either the MP40 spring system is lighter or the original springs are worn and loosing power. I recall reading somewhere that the FBP system used stronger springs. (maybe incorrect?) My thought was simply to install either a new MP40 spring set from Wolff and if they were too stiff, simply cut a coil or two off so that it would run the ammo I'm already set up to reload. (I know I could increase the powder drop, etc. but I'm currently loading with WST and the pressure curve begins to increase dramatically if I begin to add .5 grains or more.) Life would just be better if installing a lighter spring could magically allow my MP40 to run the same ammo I run in my competition pistol.

 

If anyone has alternative suggestions on how to run my softer reloads, please post.

 

Black River Militaria, if I choose to attempt to install different springs in my FBP recoil assembly, it appears there are two holes in the face of the assembly in which I could put a tool to unscrew the face/top. Is that correct? (see picture on first post please)

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