Two guns not up to spec.

So, a couple of guns are playing up. The newest is a JG-108 - basically an MP5 sized G3 rifle complete with sliding stock. Sometimes known as a Heckler & Koch MC51 - although, technically, it's not; an HK51 variant would be a more accurate description. It seemed like a good idea at the time. On reflection, I should have bought the Classic Army version. The other is a G&G UMP bought second hand without a gearbox. The idea was to custom build a V3 gearbox for it but the UMP gearbox requires some custom bits so I caved and ended up buying a complete new G&G gearbox. Again, it seemed like a good idea at the time... :)

Both guns are firing at around 255-265 fps. They should be around the 330 mark.

It's probably air-seal issues with both. I've discovered in the past that no amount of fiddling I've done will fix air-seal issues on A&K, Cyma or Jing Gong guns. The best solution  I've found is simply to replace the cloned part with the original or an aftermarket bit. In this case, for the HK51 a Tokyo Marui Hop Chamber, Lonex Airseal nozzle, Lonex Cylinder, Lonex Bearing spring guide and an M100 spring should put that right. I've got shed loads of Nitrile o-rings so I'll swap that as well. 

With any luck the UMP is just a piston head o-ring problem but, I've got another M100 spring on order so I can swap that over if needed. The battery compartment door is not staying closed; the door itself is fine it seems to be the notch in the upper receiver that has worn. A bit of brass cut to shape and epoxied in should solve that. I can't remember but I think I fitted an SHS high speed motor in either this one or the DE one but I've got a spare Lonex A1 short motor that I'll drop in if its a standard one. The G&G has been rewired to deans and I've recently bought a couple of 9.9v LiFePo4 batteries which fit - just.

On a side note, although firing at a more respectable 320fps and despite using a 20C 7.4v Lipo, the TM Type 89 is firing a tad slow for my liking; that 700rpm sewing machine noise just irritates me. I've ordered a Lonex Titan A3 high speed motor which will hopefully be an improvement .