GSG MP40 light primer strikes

[68coupe]

I have this GSG semi-auto MP40 that has been having light primer strikes & increasing in frequency lately. Has anyone else experienced this and figured out what is causing it/how to fix it?

 

Thanks in advance, Karl

[reichstall]

sounds like main spring getting weak

[Petroleum 1]

Just one type of ammo??

[NFA amnesty]

I assume you checked your barrel collar and made sure it is still tight? They usually don't come loose but no harm in checking it. I have never looked at a semi-auto and the bolt set up so not sure how it is configured but make sure the bolt freely moves (oil it) and ensure it goes into battery.

 

As Vinn mentioned, have you tried different ammo manufacturers to see if you have the same problem?

 

Wish I could be more helpful.

[68coupe]

I've tried several types/brands of ammo. It WILL NOT eat any 147gr (nose of bullet too blunt to feed properly), but will consume some types of 124gr. It seems to prefer 115gr. It's really fun to shoot, when it's working. The bolt moves quite freely. At first, it ran well, with the light primer strikes coming infrequently later on. Now it occurs with every mag, several times. I have followed cleaning instructions per the manual, but feel that they are inadequate. They state that no real attention is required for the lower save a little light oil around the hammer. I have never attempted to disassemble the lower to get a look at the trigger assy or how it functions internally. I can't find anything with my many internet searches for complete disassembly/reassembly.

 

Thanks again in advance,

 

Karl

[68coupe]

After a good "douching" of the entire lower with rem-oil, I took it for a trip to the range today, with mixed results. 1st mag ran beautifully, with no problems. Second mag, not so much. After 5 or 6 rounds, it started doing the same thing. It seems to me that the mfgr. instructions for cleaning/lubrication are woefully inadequate. Next, I will disassemble the entire lower to clean, inspect & lube. What a pain in the a$$. I expect more from the Germans. They usually do a great job of engineering and manufacturing. "Learn as you go". Any and all suggestions are appreciated, as always.

 

Karl

[colt21a]

Another 9mm fun clone and will never perform like a original. I had a new one in sbr form.Sold it to a local buddy he still has it new in box. since he has a postie and a trans original MP-40 After the MP-38 import fiasco ended i gave up on all of them.I watched "Where Eagles Dare" Twice. and also sold him off my entire German collection.

 

yeah when you get frustrated i just SELL IT.

he is a happy man.FLAGS, HELMETS, BAYONETS, P-38'S PPK, HOLSTERS,POUCHES, MAGS, SLINGS,HE CAN FILL A 12X12 ROOM. I wish you luck with the one you have. and you don't have to spend 20 g plus for a real one.have a nice year.

 

RON K.

[volker11]

I had the same problem. After months of trial and error I think I found the solution.

I did three things:
1.   In front of the hammer is the screw that holds both halves of the gun together in the front. I loosened the screw about half a turn to a turn.
2.  There is a pin in the side of the hammer. It stuck out a little bit on the right side and may have touched the frame. I hammered it in a little bit, so it is flush.
3.  I loosened the right front screw that fastens the plastic handguard about half a turn, it may have touched the workings of the hammer.

I don't exactly know which one of these things fixed the problem, but it seems something impeded the hammer and caused the light primer strikes. I fired two full magazines without a malfunction yesterday, before that I had 10 to 13 light primer strikes out of 20 rounds.
I hope this helps.

Edited February 20, 2023 by volker11

[68coupe]

Thank you Volker. I'll take another look at it. It's just been collecting dust. It was fun to shoot, until I started having issues. I've been trying to contact ATI for months now. They haven't replied.

Karl

[Rekraps]

On 2/19/2023 at 7:09 PM, volker11 said:

I had the same problem. After months of trial and error I think I found the solution.

I did three things:
1.   In front of the hammer is the screw that holds both halves of the gun together in the front. I loosened the screw about half a turn to a turn.
2.  There is a pin in the side of the hammer. It stuck out a little bit on the right side and may have touched the frame. I hammered it in a little bit, so it is flush.
3.  I loosened the right front screw that fastens the plastic handguard about half a turn, it may have touched the workings of the hammer.

I don't exactly know which one of these things fixed the problem, but it seems something impeded the hammer and caused the light primer strikes. I fired two full magazines without a malfunction yesterday, before that I had 10 to 13 light primer strikes out of 20 rounds.
I hope this helps.

Excellent point. Any friction at all will impede the hammer strike force which can cause light strikes. I don not own a GSG but is the firing pin spring loaded or free floating? That could be another thing to look at. 

[68coupe]

I FINALLY got ahold of ATI, and was able to order all of the suspect parts. A hammer spring, a hammer, two firing pins and a firing pin spring, all ringing in at a low 34 bux and change. I started with the hammer spring, took it to the range, and taaa daa, cycles & runs fine, UNTIL the last round in the mag. The bolt bound up on the lock-back bar. I took it home and disassembled it again, looking closely at the IPB (Illustrated Parts Breakdown) and got another revelation, the spring washer for the lock-back is in the wrong position. I switched it up & it runs like a gazelle. Thanks for all the feedback & input. Now I have a fully functioning GSG MP40 & few spare parts.

Karl, 68 coupe

[volker11]

On 4/18/2023 at 9:14 PM, 68coupe said:

I FINALLY got ahold of ATI, and was able to order all of the suspect parts. A hammer spring, a hammer, two firing pins and a firing pin spring, all ringing in at a low 34 bux and change. I started with the hammer spring, took it to the range, and taaa daa, cycles & runs fine, UNTIL the last round in the mag. The bolt bound up on the lock-back bar. I took it home and disassembled it again, looking closely at the IPB (Illustrated Parts Breakdown) and got another revelation, the spring washer for the lock-back is in the wrong position. I switched it up & it runs like a gazelle. Thanks for all the feedback & input. Now I have a fully functioning GSG MP40 & few spare parts.

Karl, 68 coupe

Where exactly is the spring washer for the lock-back?

[68coupe]

Excellent question Volker. There is a stud that is cast as part of the barrel, where it mates with the frame. The lock-back is mounted on it, before screwing the two halves of the upper together. If that spring washer is on the wrong side of the lock-back, it will not work properly. It needs to hold the lock-back away from the frame, not away from the barrel.

Karl