Well MP7 fps questions

[luke213]

Hey guys spent the better part of today fighting with an AEP I offered to help a friend with. Started with working on the hopup and getting it working as well as converting it to a lipo. Well those two things are done and I know these aren't FPS machines but from what I've read these should shoot between 200-240 stock. Well I've been pretty consistently in the 180FPS range and it's sort of driving me nuts.

I tore down the gearbox stretched the piston oring confirmed good compression. Greased the box and did general clean up of the china grease that was in there. Shimming looked alright and I decided to leave that be. Same FPS after reassembly. So since I didn't like the fact that there wasn't a way to do an oring between the nozzle and cylinder head I started thinking it over. I ended up shortening the end of the cylinder head that goes past the cylinder itself(which the nozzle rides in). I took and super glued an oring there after trimming the nozzle reinforcement(between the spot it rides in the tappet plate), so that I could get 100% airseal from the box going forward. So that worked, I left enough of a ridge to index the box to the hopup chamber while still having an oring making connection around the nozzle sealing that section. It's also held in by the chamber area with this setup works pretty well. After putting it back together I gained 10fps. But I'm still holding around 190fps. I tried teflon tape on the bucking, and a few other little things with zero gain. Can't tell 100% but I don't believe I'm loosing anything between the nozzle and bucking, looks like a good connection can't feel any air leaking, also don't see a piece of paper moving while cycling with it upside down.

So I'm sort of at a loss, I don't know the history of the gun so the spring in the mech box could be weak. That's about the only thing I can think of at this point since I've pretty well addressed any other place it would be leaking air. But I'm open to suggestions of things I might not have tried etc, since I spent nearly the entire day working on what I thought with be at most an hour project;) But I tend to get pissed at things like this and sit and work on it for 9+ hours until it works. Except tonight I've done that and ended up nearly back where I started, engineered some interesting things in doing it but didn't solve the FPS issue.

Take care!

Luke

[T6e9a]

I just picked up a couple AEPs to play with(teching wise). I have a few projects I gotta do first, but if I find any insight, I'll let you know.

[luke213]

Appreciate it, I'm thinking it's almost certainly the spring because I just can't see what else it would be but I'm open to suggestions;)

Also if you want next time I've got it apart I can take a couple pictures of the oring mod I did to the cylinder head, it's a little bit of a cobble but it was the only way I could think to add an oring seal between the nozzle and cylinder head fairly easily. It works and is held in by the chamber as well as super glue to the cylinder head. It does require modifying the cylinder head and I likely wouldn't have rolled the dice on it but I know that this guy I'm working on this for has a parts gun with a complete gearbox. So I figured if nothing else I've got a spare of everything in the box.

I am planning on getting that other box from him tossing it in and seeing if there is any change as well. But I suspect the solution is just getting an upgraded spring for this one. I will say though I really like these AEP's despite being difficult and weird parts. For the size they are impressive it will be interesting to see where this project goes, because if with the upgrades it's stable at around 300fps that is plenty acceptable for a side arm or CQB in my mind, and with a lipo the ROF is quite good. Right now this MP7 running a 7.4v lipo is putting down just over 16RPS which is good enough in my mind;) Probably would be even better if I took the time to shim the box properly as well.

Luke

[Ancalos]

How did you convert that into lipo? Currently I use a 9.6 NiMh and it has about 17-18 rps.

[luke213]

Couple different ways to do it. This one I took some Kydex some aluminium grounding rod and made a connector that fit on the end of the lipo so that it slides into the stock system. My glock 18c I took and made a dean's adapter from the end of an old battery so I can change them easier. But it's different sized batteries depending on handgun Vs smg. I can take some pictures of the finished setup if you'd like.

Luke

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[Ancalos]

But how could the gun handle the lipo? did you modify the gearbox?

[luke213]

Actually using a 7.4v lipo shouldn't do any more damage than an 8.4v or maybe a 9.6v. But that said it is pushing more current which could break things. My 18c has had roughly 500 rounds through it since I did the lipo without an issue. This mp7 has probably had a little over a thousand so far in testing. So hard to tell long term but from what I've heard from other guys they seem to handle 7.4v pretty well.

Once I get to a computer in a bit I'll post some more info rather than typing on the phone.

Luke

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