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MP40 recoil and buffer disassembly question


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Hello all,

 

I've recently purchased an MP40 and am waiting on my form 4 approval. In the meantime, I'm trying to acquire all the spare parts I would need to run the gun. It is listed as a C&R with the ATF and has all matching serial numbers so I want to make sure I don't break or damage any of the serialized parts. Mr. Iannamico has been kind enough to suggest I consider using a parts kit barrel, bolt and lower if I choose to shoot it, which I want to do.

 

MP 40.jpg

 

In reading the forums, I have noticed many recommendations to replace the springs in the recoil and buffer assemblies. I have found them available from Wolff https://www.gunsprings.com/MP38%20&%2040%20GERMAN/cID2/mID130/dID349 but I don't know how to install them. I have also been advised by one gentleman who told me to never take the recoil assembly apart as he did and it took him forever to get the recoil assembly back up and running again. Said it would hang up and not recoil or telescope smoothly until he manually cycled it several thousand times.

 

Can anyone give me step by step instructions on how to replace the springs? Or alternatively, tell me why I should not?

 

(I do have some experience with limited gun smithing. IE: I regularly take down my 1911's completely to clean, do a little tuning on feed ramps, triggers, etc. I am by no means an expert but have been successful in what I have attempted thus far. I have not done any staking or peening)

 

Also, on the wolff gun springs link, they offer mag springs for sale. But they are listed for 30 round mags. The magazine's I've purchased are 32 round mags and that is all that I am aware were produced for the MP40. Are they just suggesting we only load to 30 or are these springs for some magazine I'm not aware of? (I understand underloading a mag to avoid FTF but seems like Wolff would list the springs for a 32 round mag if that is how it is nomenclatured?)

 

One other question. If I switch barrel's back and forth on the gun, do I need to purchase multiple crush washers or will one be sufficient? And I guess the same question about the resting bar? I hear they break easily?

 

Any help would be greatly appreciated.

 

 

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The magazines are originally designed for 32 rounds, but they were down loaded for multiple reasons, one of which you mentioned. Another reason that more than likely applies to us modern users is that they do not like to be loaded to 32 and anything past around 28 gets exponentially more difficult. I personally only load to 25 after that it is not worth the effort/time. I can only guess, but a quick phone call to wolf springs to verify, but one might suggest that their springs are only rated for 30 and not 32, that they are not in the know the magazines were for 32 rounds, and so on.

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Congrats on your purchase!

 

My advice is colored by the fact that I never purchased any new springs and have made no mods to my all matching bnz 41 gun. But then again, I don't shoot it that much. I just never bought into the notion that a gun should be run with mismatched parts to "save" the originals. After all, it's the receiver by itself that's so valuable, and can't be replaced.

 

May I suggest shooting your gun with NATO M882 (or equivalent) before making any decisions regarding springs? That way, if there are problems, you've ruled out weak, under-performing ammo as the first cause. You want true M882, the full-power rounds with the triangular bullet profile (like WWII German P.08 ammo) and NATO cross-in-a-circle, for reliability in chambering. If this ammo works well, you can try other loads.

 

There are actually two springs inside of the Vollmer telescoping spring housing, a recoil spring, and a much shorter buffer spring. You can feel the buffer spring when you pull your bolt all the way to the rear. When firing, the bolt should move far enough back to engage the buffer spring, and be propelled forward by it. Weak ammo won't engage this spring, and your rate of fire (never very fast anyway!) will slow. Really weak ammo may not let the bolt engage the sear, and the gun will just put-put-put until the mag is empty.

 

Magazines are another problem area. The original double stack, single feel mag design is not a particularly good one and some mags will work better than others. I recommend mags maker-marked kur or 98E (Steyr) as these had the best overall quality. All original magazines held 32 rds, and were so marked. Loading to 28 or 30 rounds will increase reliability. An original mag loader is a must. It should fit well. Again, loaders marked 98E or kur fit best.

 

If you're going to switch barrels back and forth, a single crush washer will do. Just re-use it. If the barrel is original and the staking on the barrel nut has not been disturbed, then I recommend not removing the barrel. Doing so will disturb the gun's original factory targeting and lower the gun's value. Same for the staking on the recoil spring housing, IMHO.

 

All I've laid in for spare parts are a couple of extractors, which have never been needed. Beware of extractors that are original but are well used and already worn out.

 

FWIW.

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The Portugese F.B.P. SMG bolt and recoil springs are an excellent substitute for original parts and way less expensive. Also, the mags for the Vigneron will fit the MP40. Unless you want original parts as spares, the FBP parts work fine.

Belgian Vigneron SMG magazines are reproductions of the MP40 mags, work well and are very inexpensive.

There is no reason to replace the spring in the tube assembly unless there is an obvious need for it. The firing pin holder unscrews from the large tube and the springs come right out. It is difficult to imagine that anyone would have trouble with reassembley of such a simple part! The pin holder is staked to the tube after tightening. If your assembly has not been previously disassembled, the pin holder is tight and the stake is strong, if you unscrew the holder you will disrupt the original stake. On reassembly you will have to restate it, or you can use Locktite, but the damage will have been done. Minor issue, but there it is. Again, unless there is a broken spring or function issues with the recoil tube assembly, there is no need to fuss with it.

The FBP SMG bolt has a fixed firing pin so the recoil tube assembly does not have the firing pin attached to the front. These show up on gunbroker.

The entire barrel assembly can easily be removed without removing the resting bar by unscrewing the barrel nut. The resting bar only needs to be removed if the barrel collar needs to be removed. The Bakelite resting bars are very fragile. Driving out the retaining pin will damage the Bakelite which is very thin on the off side of the bar where the hole goes through and often they are very tight in the mount. Original Bakelite resting bars are extremely scare and expensive now and if yours is in good condition and has never been removed do not remove it.

If you are going to use a substitute barrel, it is advisable to replace the entire assembly so you do not have to remove the resting bar. If the bar is aluminum, there is less possibility of damage. FWIW

Edited by Black River Militaria CII
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Thanks all for your input.

 

I have not actually met my new gun yet. It is in jail right now at the FFL.

 

Black River Militaria, thanks for the detailed description of the recoil disassembly. The gentleman I previously spoke with evidently didn't know what he was doing. Simply unscrewing the firing pin holder to remove the springs makes much more sense and fits in with my concept of the German mind for engineering. Does the firing pin holder require a special tool to unscrew or does it have any pins,etc. Or is it as simple as using your fingers?

 

Also, thanks for the vote of confidence on the FBP bolt. I've read mixed reviews but knowing of your experience, I'll go ahead and purchase one. I already own a STEN MKII and love the simplicity of the fixed firing pin.

 

 

 

TSMGguy, thanks for info on mags and ammo. I already load my 9mm for my STEN (load it hot) and figure the same loads that function it well will be equally reliable in the MP40? Regarding the mags, I did purchase a loader (ghn 40) and it works but does not clip in as securely as my STEN loader on STEN mags. The hook is a little worn but I don't see a way to repair it other than perhaps welding a little metal back on the hook and reshaping. But would that really be worth the effort? Life is too short for some perfectionism.

 

ghn 40.jpg

 

The mags are a different issue. I have already purchased 8 spare mags, of which 6 are the manufactures you suggest. So, guess I was lucky on that part. One of the mags I purchased was dented and I thought I could reshape it using my STEN mag tools.

 

Damaged mag.jpgSTEN armours tools.jpg

 

Unfortunately, the mandrel doesn't fit into the shell. The mandrel is too wide. I had assumed since the STEN mag was something of a copy of the german design of the mag, that the mandrel would fit, but now I know I was wrong. In cleaning the mag, the follower functions correctly without any hang ups but when loading ammo, the double stack won't push the cartridges past the dent. I've considered cutting a wood mandrel and trying to run it through the shell to push the dent out since I'm not trying to adjust the feed lips, only the outside dimensions of the shell. But if anyone else has experience or suggestions, I'm always open to ideas.

 

 

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Hi Imageaudio,

 

The Sten mag is a copy of a German magazine for the MP-28. So much a copy that they interchange. Unfortunately I don't have experience with body & fender work required to fix the magazine.

 

Enjoy your new piece.

 

Grasshopper

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Personally, I would put the original bolt and recoil assembly in the gun safe and find an FBP bolt and recoil assembly to shoot with. You won't have to undo any staking on your original parts and you will have eliminated about 90% of the actual moving parts in the system from wear and tear. Install a Wolff spring kit in the FBP assembly and find a replacement extractor (just in case). That should hold you for the next several decades of shooting.

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The ghn mag loader is one of the ones that's been often reproduced. (Look closely at the WaA eagle on yours). Some won't slide onto a wartime mag at all because they're too tight. You really do want to find a 98E or kur loader. You'll be happy with how it fits and locks into place.

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Question, the Sten magazine tools, will they set the feed lip too? Or are they just for removing dents?

The following statement is in reference to Sten mags. I do not have experience with MP40 mags yet.

 

The mandrel usually comes with a tool that helps form the lips. The mandrel slides all the way into the magazine up to contact the feed lips and then the tool goes over the feed lips. A few hits with the hammer and the feed lips are supposed to be correctly formed.

 

STEN armour's mag repair tool directions.tiff

 

I have found however that with some worn lips, they don't form perfectly. In this case, I attempt to tune the lips a little more by gently hammering them over a conical punch. Usually, the tuning requires bending the lips near the base of the cartridge in just a little more. Some articles state that feed lips on a Sten mag are supposed to be parallel but that has not been my observation. The mag feed lips are typically at about a 3 degree angle from horizontal on the mag. But the cartridge needs to be presented about about an 8 degree angle. The measurements are provided in Peter Laidler's excellent book on the sten in a sketch on page 327.

 

Sten Mag Lips correct dimensions copy.jpg

 

 

The area of the mag feed lips that retain the base of the 9mm cartridge needs to be 0.330 wide and the mouth area of the feed lips needs to be 0.360 in width. So, while the feed lips appear to be parallel to the naked eye, they are actually spread just a little wider towards the front of the feed lips.

 

Final note is that after much patient experimentation and observation, I've come to the conclusion that some mags are just too worn to mess with. They won't hold their shape for very long even if you download to 20 something rounds. While Sten mags are becoming more expensive, the cost is not so prohibitive as to simply buy a few more and pass the old ones that don't work along to collectors of dummy guns or someone else who is not trying to get them to run in a full auto Sten IMHO.

 

In summary, the armorer's tool is a neat piece of history and works in some instances. But it is not a cure all fix. If you want one for your collection, it may be worth the price. But if you just want something to fix your mags, I conical punch is a much more economic method to accomplish your task and can be adjusted to form any angle you need for your feed lips. And as I posted earlier. The Sten tool only works on Sten mags. The conical punch can be used on any type mag. (just one small tool to carry in your range bag when running tests!)

 

I use an old snap-on tools 3/16 center punch.

 

Center punch.jpg

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  • 10 months later...

I bought this spare some time ago with the thought of switching it out of my C&R BNZ41 MP40 to preserve the original with a matching number. It seems to be in very good condition. From a post above, it sounds like I would need to put some locktite on the threads that screw in and hold the assembly together, is that correct? If so, what type (color) locktite should I use? I tried to take the picture in the bright light but there are some shadows. Thanks. Robert

IMG_20171130_101837053_HDR.jpg

Edited by Robert Henley
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Sorry for the sideways pic it always does that with pics from my iPhone. I would use the blue for starters, clean the threads with some alcohol and go for it. If that doesn't hold go with the red threadlocker. I only use the red as the last resort as it is a pita to remove requiring some heat to get the parts to move.

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I pulled the original numbers matching recoil firing pin assembly from my BNZ41 MP40, and it indeed looked to be staked where the firing pin assembly screws into the rest of the assembly. So thinking about putting the above mentioned extra assembly in the gun and seeing how it does. The MP40 continues to amaze me with its great quality and engineering. A terrific gun from 76 years ago. Robert

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