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I bought a Fleming MP5 conversion with an autosear and I'm having a huge problem with the gun destroying carriers and locking pieces. The first time this happened I went to disassemble the carrier group and the locking piece would't come out of the carrier. I gave it to an MP5 armorer and he put it through an ultrasound bath and had to remove the locking piece with pliers. He said the locking piece was slightly bulged in the rear and was catching inside the carrier. He removed a slight amount of material from the looking piece using a lathe to get it back in spec. I bought a new locking piece recently and it would't fit in the carrier. Just bought a new carrier this week and installed the new locking piece with my existing German bolt.

Approximately 400 rds. into my range session today and the gun started firing at a crazy high cyclic rate and I noticed when my buddy was shooting that there was a lot of fire coming from the ejection port as if it was unlocking prematurely. I stopped firing and headed home. Same issue as before. The locking piece would not budge free from the carrier. I kept spraying it with oil and finally got it out using some vice grips. I cleaned everything up really well and the locking piece won't fit into the carrier at all. It seems like the same thing happened again where the rear of the locking piece is belled ever so slightly to where it won;t fit in the carrier. Now I'm down two locking pieces and two carriers. Any idea what the hell is happening?

I was using a new recoil spring assembly with the new locking piece and carrier.
 

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If the bolt gap cannot be corrected with rollers it has problems with the trunion and barrel set. Basically if you cannot adjust the bolt gap with replacement rollers I recommend contacting one of the fine HK Smiths on this site and send the rifle to them.
 

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If the bolt gap cannot be corrected with rollers it has problems with the trunion and barrel set. Basically if you cannot adjust the bolt gap with replacement rollers I recommend contacting one of the fine HK Smiths on this site and send the rifle to them.
Why could a new locking piece not also help correct the bolt gap.
 

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The face of the bolt hits the face of the chamber end of the barrel. The angle of the locking piece and the inertia of the carrier plus the push of the recoil spring pushes the rollers into the recesses of the trunnion. If the face of the barrel is too far into the trunnion, the rollers are not held into the trunnion and against the locking piece tightly. So the rollers aren't in place to divert the right amount of recoil energy into the trunnion or the bolt group for proper function. The angles need to be precise and everything needs to be tight or the system is imbalanced.

By the same token, the barrel can't be too far out of the trunnion. If it is, the the rollers aren't deep enough into the pockets of the trunnion and again the angles won't be right and the right amount of recoil energy won't be diverted to the trunnion or the bolt group for proper function. That is why the proper bolt gap is so important.

Scott
 

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Are there any roller marks in the rails anywhere? What stock are you using? Does it have the proper buffer in place?
 

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Why could a new locking piece not also help correct the bolt gap.
Grasshopper, we were all new at one time to the roller locks, so enjoy the study and journey as all us have made. Read, learn, read, learn and then ask questions. Your problem is not the LP it is bolt gap that maybe (if you are lucky) corrected by replacing the rollers with a different size. Worst case you have bigger problems as I mentioned. It all can be fixed. MG's are like race cars, they require maintenance that most owners can perform, but the bigger problems will have to require skilled talent.
 

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Why could a new locking piece not also help correct the bolt gap.
It can, provided the existing locking piece is worn significantly. Bolt gap is not likely all of the problem, I believe. This is the first time I've personally heard of the issues the OP is having, with all the thousands of roller types out there, I'm sure we'd have heard of this before it it were a simple bot gap problem.
 

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The LP will need to be replaced, but you will also be changing rollers (at best). My guess is you have a trunion / barrel issue.
 

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I bought a Fleming MP5 conversion with an autosear and I'm having a huge problem with the gun destroying carriers and locking pieces. The first time this happened I went to disassemble the carrier group and the locking piece would't come out of the carrier. I gave it to an MP5 armorer and he put it through an ultrasound bath and had to remove the locking piece with pliers. He said the locking piece was slightly bulged in the rear and was catching inside the carrier. He removed a slight amount of material from the looking piece using a lathe to get it back in spec. I bought a new locking piece recently and it would't fit in the carrier. Just bought a new carrier this week and installed the new locking piece with my existing German bolt.

Approximately 400 rds. into my range session today and the gun started firing at a crazy high cyclic rate and I noticed when my buddy was shooting that there was a lot of fire coming from the ejection port as if it was unlocking prematurely. I stopped firing and headed home. Same issue as before. The locking piece would not budge free from the carrier. I kept spraying it with oil and finally got it out using some vice grips. I cleaned everything up really well and the locking piece won't fit into the carrier at all. It seems like the same thing happened again where the rear of the locking piece is belled ever so slightly to where it won;t fit in the carrier. Now I'm down two locking pieces and two carriers. Any idea what the hell is happening?

I was using a new recoil spring assembly with the new locking piece and carrier.
I feel your pain http://www.hkpro.com/forum/hk-long-gun-talk/313625-mp5-locking-piece-stuck-going-out-carrier.html I sent mine to my GS as well........FWIW I checked my bolt gap I believe it was on the low end or under just put some +4 rollers in brought it into spec but not by much I am going to def keep an eye on it based on what yours did.

This is the first time I've personally heard of the issues the OP is having, with all the thousands of roller types out there, I'm sure we'd have heard of this before it it were a simple bot gap problem.
Just last week http://www.hkpro.com/forum/hk-long-gun-talk/313625-mp5-locking-piece-stuck-going-out-carrier.html I would have thought noway on the bolt gap but after reading OP experience and checking mine after I got mine back I am second guessing.......
 

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Who setup your sear? Did they use a properly retimed hammer?
 
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