MP40 Buffer Spring Replacement

[hatrick]

Do you have to remove the firing pin in order to replace the buffer spring?  I really don’t want to remove that staked pin that holds the firing pin in place. 

Thanks

[Rekraps]

No, you do not. The buffer assembly has (I'm on the road today or I'd pull my units out) three separate pieces with individual springs. If I remember correctly the firing pin/firing pin retaining nut (pin is pinned to the nut) screws on. When I get home tonight I'll pull my extra buffer assemblies and provide more details. What I like about the  buffer assembly is that in its disassembled state, it collapses into a easy to store package. 

Also, remember that the FP is serial numbered to the gun..

[Rekraps]

I'm probably wrong.... again, when I get home I'll pull my units out and provide details.

[hatrick]

Thanks for the help. I was able to take apart the three telescoping sections and remove the main recoil spring but the buffer assembly is still attached to the back of the firing pin assembly. It it really solid so I’m not sure how the buffer spring tube is attached to the back of the firing pin. 
 

Thanks

[TSMGguy]

MP40 bolt and Volmer telescoping recoil spring housing diagram. Note that there are two springs, the recoil spring, and the buffer spring. The buffer spring has its own guide.  

[hatrick]

I’ve stared at this diagram for a few days and just can’t figure out how parts 46 and 47 are connected. Odd diagram since it doesn’t seem to have recoil/buffer assembly parts in the correct order. The buffer if I’m not mistaken are parts 51 & 52 inside of part 47 which then attaches to 46. 

[Rekraps]

TSMG to the rescue! I love the diagram. 46 and 47 are not joined at all . #46 serves as a "stop" for 47. For me the hard part is separating the firing pin from the firing pin retaining nut. Be careful especially if the FP is matching SN. I just bought two spare buffer units. 

[hatrick]

So in order to remove the buffer and replace the buffer spring you need to remove the pin holding the firing pin in place correct and remove the firing pin? Then the buffer spring tube (47) slides through the firing pin retaining nut (46) and the firing pin is reinstalled. Basically in the end the buffer spring assembly becomes a single unit with the firing pin and firing pin retainer nut.

I really don't want to remove the firing pin if at all possible since it is staked in place.

[TSMGguy]

58 minutes ago, hatrick said:

So in order to remove the buffer and replace the buffer spring you need to remove the pin holding the firing pin in place correct and remove the firing pin? Then the buffer spring tube (47) slides through the firing pin retaining nut (46) and the firing pin is reinstalled. Basically in the end the buffer spring assembly becomes a single unit with the firing pin and firing pin retainer nut.

I really don't want to remove the firing pin if at all possible since it is staked in place.

I've never had to remove or replace the firing pin on my MP40, so can't help much. Like you, I want to keep the factory staking undisturbed. Hopefully BRMCII will weigh in. He's got plenty of experience with these guns. 

Is your buffer spring needing replacement?

[hatrick]

I don't think my buffer spring needs replacement per say but I picked up a spare complete recoil assembly so I don't risk breaking the original matching numbered part and I figure on my spare I may as well replace the springs with Wolff springs since it will be my shooter recoil assembly and I may as well have brand new springs to reduce overall wear on the rest of the gun.

[TSMGguy]

I picked up many MP40 original spare parts over the years, but none were ever needed. Acquiring them was enjoyable, though. As was selling them. My parts stash is down to one each armorer's spare firing pin and an extractor, both WaA623 inspected. The MP40 is not often fired. Other less valuable guns scratch the Class III itch!   

[Rekraps]

Listen to TSMGguy, and NO the firing pin does not need to be de-pinned in order to replace the springsl.

[hatrick]

That’s encouraging to hear test you can replace both springs without taking the firing pin retaining pin out. I guess my buffer tube is just stuck in the firing pin retainer nut as it doesn’t want to come off. Any advise on getting if off?

[Rekraps]

3 hours ago, hatrick said:

That’s encouraging to hear test you can replace both springs without taking the firing pin retaining pin out. I guess my buffer tube is just stuck in the firing pin retainer nut as it doesn’t want to come off. Any advise on getting if off?

I just pulled both my "extra" buffers out and the piece that fits in the firing pin retainig nut on one is tapered, two piece. The other is not tapered two piece. 

So here is the official answer. The buffer piece that fits into the firing pin retaining nut is removed ONLY when you remove the firing pin. It then slides out the hole. the firing pin retaining cross pin (that holds the firing pin in place) will have to be pushed out and the firing pin removed. Only then will the two piece smaller buffer(s) with spring be able to be removed. 

So we were wrong. 

[Rekraps]

I am sorry for the misinformation earlier. I had to get home and pull out the parts. So much for old man memory!

[hatrick]

No worries at all. I’m so thankful for the time and help! Thanks so much for confirming things and the great pictures. I think I’ll just swap out the recoil spring and leave the buffer spring alone. A new Wolff recoil spring should be more than enough to help reduce wear and tear. Replacing the buffer spring would have been great but it isn’t worth messing with the original staked firing pin. 
 

Thanks again!

[Rekraps]

2 hours ago, hatrick said:

No worries at all. I’m so thankful for the time and help! Thanks so much for confirming things and the great pictures. I think I’ll just swap out the recoil spring and leave the buffer spring alone. A new Wolff recoil spring should be more than enough to help reduce wear and tear. Replacing the buffer spring would have been great but it isn’t worth messing with the original staked firing pin. 
 

Thanks again!

I tried to remove the firing pin you see in the unit above and the retaining pin did NOT want to budge. I just left it as is. The internal spring in that part is essentially sealed and just can't go bad. 

[StrangeRanger]

I don't own an MP40 and have no interest in ever doing so but I read this thread and look at the parts breakdown of the bolt ass'y and all I can say is what a Godawful complicated mess.  Typical German engineering: why use one large simple part when you can use 5 small complex ones instead.  Has anyone ever looked at making a replacement system that used a simple bolt like a Sten Mk2, an M1A1 or a Beretta 38/44 as a replacement? Even a separate FP with a heavier spring but without the buffer like an MP28/II or a Lanchester would be an improvement.

[hatrick]

Rekraps... that pin must really be in there tight if you can't knock it out. I wonder if it is tapered and needs to be removed only in one direction. I agree that it really isn't worth it unless that buffer spring really feels shot. I'd rather not remove an original pin for no sure reason. A new main recoil spring should be more than enough to keep the wear to a minimum. My recoil spring has a very slight kink/twist to it which is why I want to replace it. I'll probably order a spare butter spring just to have in case of an emergency since Wolff has them and it is only $4

Strange Ranger... I think the reason they went with a telescoping recoil assembly is that now that they were making stamped receivers they didn't want any risk of springs binding. The old milled receivers like the MP18, Lancaster and Beretta were more robust and conducive for a larger heavier spring. I certainly am not going to ever argue the overly complex German designs and it amazes me the simplicity and dependability of the MP18 and how that jumped to the MP40.

[StrangeRanger]

FWIW The Beretta receiver was formed out of sheet metal and the Lanchester and Sten receivers are made from tubes not milled from billet.  The MP40 looks like it was designed by a guy who made cuckoo clocks in civilian life

[TSMGguy]

The reason the Vollmer telescoping recoil spring assembly was adopted was not because it was a better idea. It was because Haenel owned the patent and wanted to collect the royalties on each gun produced. STEN and Swedish K submachineguns proved that a big, exposed recoil spring was easier to produce and worked just fine.

Same with the MP38 & MP40 Haenel patent double stack, single feed magazine design. A double stack, double feed magazine would probably have worked better and been less prone to jamming. In 1942 the Germans introduced measures to improve magazine reliability. They included the pressing of ribs in the magazine bodies to reduce internal friction, and the issuing of magazine cleaning brushes. Feeding problems were never fully solved.

I know the Germans did not internally lubricate MP40 mags in extremely cold weather. I also find that original mags seem to work better if no grease or oil is used at all.      

[StrangeRanger]

Profiteering, graft and corruption in the Third Reich? I am shocked! Shocked! Didn't the Nazis claim that sort of behavior only happened in weak decadent democracies?🤣

[Rekraps]

And, the bolts of the MP 18, 28, MP40, Sten, & Lanchester are all remarkably similar. Its the recoil spring design that varies. 
As it turns out, the larger diameter recoil springs function best and have lithle tendency to kink or bind.  The Swedish K is the pinnacle of open bolt simplification   

[Mad Machinist]

On 12/2/2023 at 3:01 PM, StrangeRanger said:

FWIW The Beretta receiver was formed out of sheet metal and the Lanchester and Sten receivers are made from tubes not milled from billet.  The MP40 looks like it was designed by a guy who made cuckoo clocks in civilian life

What beretta reciever are you referring to as sheet metal.......the M38 and M38/44 stuff I have is all machined......

[StrangeRanger]

The receiver of the 38 series guns is actually formed into a keyhole shape from a flat sheet rather than a tube and is then machined after forming.  Look at where the sides of the trigger housing abut the receiver. There are no welds present.  There is a visible radius where they have been shaped.