Day 39 - Monday 3rd December
We'd taken the M2 out for a skirmish on the 25th November for another trial by fire where it recieved some 'extensive testing' to check out the modifications we'd made. Two issues were raised: we noticed that the gun became weaker FPS-wise and that the RPM had dropped to about 300rpm. On closer inspection we found that the barrel was coming loose from the hop-up unit and trying to down the barrel. The return springs looked unchanged but it was pretty clear that they'd slackened a bit.
After a bit of dicussing we came up with some ideas to fix this problem. First we removed the PSG-1 barrel and worked out that we could put a circ-clip between the plate and hop-up unit to stop it moving forwards. A few minutes on the lathe and the circ-clip groove was cut :)
Apologies for the quality of the photos, I'm without my camera and have had to resort to taking the pics with my phone (and that's why there's only 4 pics) :o
We attach a new plate and stainless steel rod to the tappet plate extension. We use an old AEG spring out of an MP5K for the spring
Assembled onto the piston:
Installed in the gun:
In an interesting turn, the 4 return springs at the front coupled with the new AEG spring proved too much and would send the gun into a bizarre full-auto half-firing cycle, so we disconnected two of the front return springs with fantastic results: We had a theory that the AEG spring would also serve to up the FPS, we weren't sure just how much by. We tested it and we were getting a reported RPM of 410 and a pretty consistant ~375fps with only 120psi which is a nice improvement as we were having to go to 145psi to get that kind of FPS :)
Now we need to modify the tappet plate so it opens the valve quicker, hopefully this will also allow us to re-attach the two return springs and get nearer 500rpm and higher FPS - even though we've surpassed the FPS level (350) we want to make the system as efficient as possible, we'll attach a air-bleed so we can bring the FPS down to legal playing limits and even tune it down to 328fps for away-games.