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MP7 Gas efficiency Problems


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#1 lorddave551

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Posted 12 April 2013 - 03:01 PM

Hey guys first post here and what else its about a problem :/.  This particular mp7 is roughly 1 yr old but hasnt been used in about 3 months i'd say.  Before beginning here's a parts list:
Dytac enhanced recoil spring
Ra tech enhanced recoil system

Ok now the problem:  This MP7 refuses to finish a magazine even on semi automatic.  About 30 shots in the bolt no longer recoils enough to load the next bb.  When the enhanced recoil spring is replaced with the stock recoil spring the mp7 BARELY finished the magazine.  Additionally after the bolt stops recoiling or the magazine is empty, manually dumping the mag's gas reservoir shows that there is plenty of pressure left.  This problem manifested with all 4 of my 40 round mags.  I'm not sure whats going on at this point.  From what i understand these mags are supposed to hold enough gas for 1.5 to 2 magazines.  Prior to this the gun worked just fine with the enhanced spring...

I think the problem may be either a worn hammer spring or a worn hammer, but i've heard reports of neither producing a problem like this...  I do have a 150% hammer spring lying around but im not sure if installing this will address the issue.  Thanks for any feedback!

#2 lorddave551

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Posted 12 April 2013 - 04:23 PM

Update:  Installed 150% hammer spring

It appears that the bolt is not traveling very smoothly.  Manual cocking of the mp7 does not feel smooth and sometimes the bolt even locks up upon release and does not return to battery.  I think the increased spring strenght may be pressing the hammer up on the bolt but im not sure how i would fix this.  If anything this aggravated the problem

Edited by lorddave551, 12 April 2013 - 04:41 PM.


#3 General Pickle

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Posted 13 April 2013 - 09:37 PM

So you've upgraded the recoil spring to be stiffer? If that's the case... there's yer problem. That increased strain on the blow back action forces it to use more gas and is likely sucking away more power than it normally does. This is often a problem in M4 GBBR's when they're given stronger buffer springs, as the load that the blow back has to push is now much more than it was meant to handle. Did this problem occur before you installed the recoil spring or did it only start happening after you installed it? That could narrow it down.

Good luck!

#4 lorddave551

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Posted 13 April 2013 - 10:57 PM

It had no problems with the enhanced recoil spring before and its been installed in this MP7 for about  year now.  But as i previously stated, even when the enhanced recoil spring was swapped out for a stock recoil spring the MP7 BARELY finished the magazine on semi auto(both recoil and sound were EXTREMELY weak).  It does not finish a magazine on fully automatic fire with the downgraded spring either.  These tests were also run in 80 degree temps and the magazines were allowed to warm up before firing.  Emptying the magazine's gas reservoir reveals plenty of leftover pressure in the mag, but for whatever reason it isn't making it into the gun.  This problem manifests itself in all 4 of my high cap magazines.

Edited by lorddave551, 13 April 2013 - 10:58 PM.


#5 General Pickle

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Posted 13 April 2013 - 11:03 PM

Have you taken a look at the bolt assembly? See if you can find a person with an MP7 that works fine, test the mags with that gun and see if the problem persists. I'd say it sounds like something is wrong with your gun, but who knows it could be worth a shot. Look at the NS2 nozzle carefully and see if there's any cracks or deformations. Also pull the nozzle forward to check the internal seal; that is the part that always worries me most, as it provides all of the seal for the blowback and the firing gases. How often do you clean/lube the gun and/or the nozzle? What lube do you use?

#6 lorddave551

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Posted 14 April 2013 - 07:50 PM

On the nozzle i did not see any cracks/deformations, there is a small amount of damage at the very back of the piston where one of the return springs got chewed up.  I have examined that area particularly closely and found no cracks.  

However, i do believe you are right about the internal seal.  After completely disassembling the bolt i checked the seal between the reddish plastic head and i found the seal to be a bit loose.  I was able to slightly wiggle the piston head in the nozzle which im guessing is bad since this is supposed to be an airtight seal.  I think you may be correct in saying this is the source of the issue.  I had similar problems with a 4 yr old marui 1911 and an upgraded piston head solved the issue.  Luckily, evike sells an upgrade part by pro arms so i'll pick that up in day or two and test it out.  Thanks for the help and i'll keep you posted

Edited by lorddave551, 14 April 2013 - 07:51 PM.


#7 General Pickle

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Posted 14 April 2013 - 10:45 PM

No problem! I look forward to hearing the verdict. My MP7 hasn't had gas issues, but there was a point where a piece of the rocket valve came off and lodged itself inside the nozzle return springs... it seems that is rather rare, but in any case it made me open up the bolt to fix it which in turn gave me a really good look at what was going on inside that whole assembly. Perhaps you could simply tighten the head? I assume you'd have tried that but ya never know, and I mean who doesn't like new parts anyway :P

#8 lorddave551

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Posted 15 April 2013 - 03:39 PM

Picked up the ugrade part and it still has not solved the problem.  I'm at a loss now.

#9 General Pickle

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Posted 15 April 2013 - 07:27 PM

How is the range? Do you notice a lot of excess gas coming out of the muzzle or breach? My next guess is that maybe the seal between your hop chamber and loading nozzle is not functioning properly, so perhaps that gas isn't going where it is supposed to? Aside from that I really wish I could do more, without looking at it in my hands it's just kind of speculation. See if you can post some pictures that might better describe the problem, or maybe we'll be able to identify some parts that need repair/are missing.

#10 lorddave551

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Posted 16 April 2013 - 03:19 PM

I don't notice excess gas popping out of the breech upon firing.  Haven't checked the muzzle since its covered by a barrel extension but i'll make it a point to do that.  I've since replaced everything with stock parts and tightened everything up i could think of and i think i fixed the power issue although i'm not sure how.  FPS looks pretty stable and i can now finish a magazine on automatic, i wont be able to verify fps stability until i get my hands on a chrono.

That being said, another issue has popped up due to swapping out the stiffer recoil spring for the weaker stock one.  In short, after loading in a new magazine and releasing the locked bolt, it fails to return to battery.  Here's a picture of the problem.  Notice the small gap between the bolt and frame.  The bolt will also semi occasionally fail to return to battery mid magazine but again this is rare.  The only way to get the gun to fire is to eject the magazine, recock and release the bolt, and then reinsert the magazine.

Heres a picturePosted Image

Edited by lorddave551, 16 April 2013 - 03:24 PM.





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