MP40 Barrel Nut Retaining Washer Installation Instructions

[hatrick]

Can anyone explain the proper procedure for installing the thin barrel nut retaining washer and getting it properly aligned and getting the tabs peened to properly lock the barrel retaining nut. Is there any specific tightness the retaining nut should be tightened to or is basically as tight as possible (within reason)? Does it matter which way that thin washer faces?

Any help would be greatly appreciated as I don't want to damage anything since all the numbers are matching. Very odd that it is missing to begin with.

Thanks

[TSMGguy]

Photo of barrel nut and locking washer that have not been tampered with. Reproduction MP40 barrel nut locking rings have been available in the past. It looks to me that the factory used a small square tapered punch to stake the ring.

The MP40 is of mostly of pinned construction. Staking was used extensively, which prevented tampering at the user level. An MP40 that has not been disassembled past field strip is a rare bird today.

 

Edited December 12, 2023 by TSMGguy

[hatrick]

So is it as simple as putting unscrewing the barrel nut and removing the barrel, sliding the washer on and retightening the barrel nut as tightly as possible and then peening the tabs towards the muzzle?

Is there anything I need to align or be aware of or is it that straightforward?

I want to make sure I get this right. 

Thanks

[DARIVS]

That is correct.  The barrel nut should be tight, but I am aware of no specification for torque.  The staked washer only ensures that vibration or temperature change will not loosed the nut over time, as well as act as a temper proofing device.   The barrel's rotational angle is ensured by the locking slot and tab so tightening the barrel with a spanner with the receiver in appropriate vice won't cause any front sight cant.  When I changed my barrel (which was already mismatched), the original staked washer cracked and broke, so I carefully fabricated a couple new ones to use from sheetmetal of the same thickness, and they are indistinguishable from originals.  Stamped reproduction washers are available, but the two tabs on the washer had radiused corners, not sharper ones like the original washer I removed.  The original washer was not flat either.  It had a circumferential step or offset stamped into it, making it function as a crush washer.

[TSMGguy]

The bnz 41 gun in the photo three posts above is mine. The barrel nut has never been loosened, and the barrel has never been removed. The staking on the locking ring is factory original. While the barrel and nut are tight, the sling mount still wiggles slightly. I won't be "correcting" this, or the slight wiggle between the folding stock and the grip frame. Both conditions existed when the gun left the Styer factory. My OCD only goes so far!

Edited November 20, 2024 by TSMGguy

[tommyboy]

Here’s another picture of a gun with a barrel nut that’s never been removed since original assembly.

[hatrick]

Thanks guys… this is super helpful! I think I’m going to make a “wrench” from a 2x4 in order to not risk marring the barrel nut.

I already have an original ring as well as a DK Productions repro ring as a back up. 

[tommyboy]

You can just use an adjustable wrench with leather or some other material inside the jaws to prevent metal on metal contact. The nut is not usually super tight.

[hatrick]

14 minutes ago, tommyboy said:

You can just use an adjustable wrench with leather or some other material inside the jaws to prevent metal on metal contact. The nut is not usually super tight.

Good to know the the nut isn’t crazy tight. I certainly don’t want to over torque it. 

[StrangeRanger]

I don't know crap about MP40s but in trying to follow this thread I found this on YouTube:

https://www.youtube.com/watch?v=NlHj3nEg0v0

If you haven't seen it you should.  Aside from being informative, it's a very impressive piece of work. He's done a lot of similar videos for other guns including a 1928 TSMG

I think Heinrich Vollmer must have owned stock is a company that manufactured roll pins

 

[Rekraps]

Great info you guys! 

[TSMGguy]

Have not noticed any original roll pins on the MP40. They seem to be solid with concave ends allowing peening. They're easily driven out using a punch that's about half of the diameter of the pin.  

Edited November 21, 2024 by TSMGguy

[Rekraps]

5 hours ago, TSMGguy said:

Have not noticed any original roll pins on the MP40. They seem to be solid with concave ends allowing peening. They're easily driven out using a punch that's about half of the diameter of the pin.  

Interesting. My MP40 (BNZ41) was an unmolested numbers matching gun and the roll pins did not seem solid, but were flared at each end when installed. 

[hatrick]

I’m ready to give this a try… any advise on holding or clamping the receiver or barrel so not to damage anything? The stamped receiver makes me a bit nervous. 
 

I’ve got it soaking in Kroil right now… should I also warm it up with a heat gun?

Edited November 23, 2024 by hatrick

[hatrick]

I can’t get that muzzle nut to budge and I don’t want to damage anything. I may have to have John Andrewski or Robert at Black River take care of it for me. 

Edited January 4 by hatrick