G&P M4 double firing and locking on semi.

[SunSpectre]

I have a custom built M4 with an aftermarket G&P 8mm bearing gearbox that had an m120 spring in it, which i changed to about an m90 for 300-330 fps. The motor I had was a stock SRC which wasn't able to pull the spring all the way due to the bearing which provided a little more compression than the motor could handle, so i removed this and all was fine and well. Not I have put in a G&P m120 motor and the rate of fire as shot up (between 15-20 rps is my guess) which sis great, but on semi the trigger is responsive but if i pull it multiple times very quickly it sometimes double fires on some shots or doesn't cycle on others and sometimes locks up. This was a problem the SRC motor did not have on semi and fired as fast as i could pull it. By double firing on semi i mean it is able to cycle twice before the anti reversal latch cuts off the system, not that 2 bbs come out in one cycle. All of this has been done on a reasonably charged 8.4v large type battery. Any help?

Thanks guys

[dave38x]

Re: G&P M4 double firing and locking on semi.

Over-run would be my guess - your gearbox isn't stopping quickly enough when you let go of the trigger and is able to wind up almost a complete cycle, causing a lockup or second shot.

[North West Outpost]

Re: G&P M4 double firing and locking on semi.

By custom I take it you mean externals are custom not the internals.

It is over run, you would not get this happening with the M120 spring.

The ARL is not in there to cut the system off it is there to stop the gear box unwinding from the tension from the spring. It catches the bevel gear where ever they stop spinning from the previous cycle. Which can lead to 'lock up.' However a properly set up gear box with ultra torque motor and decent battery can help to over come it.

Unless the spring is that long it is jamming with the bearing spring guide there is NO way it would add enough force to lock a gear box up. Who ever did your 'custom' work if they new what they were doing would have short stroked the gear box to bring the fps down keeping the M120 spring and adding an Ultra torque motor and not crappy standard one. Adding a fet will also help particularly if you wanted to add to your 'custom' work with an ASCU.

[SunSpectre]

Re: G&P M4 double firing and locking on semi.

Ok, firstly I said anti reversal latch when i meant cut off lever, the problem appears to have nothing to do with the ARL. The m90 spring is a short spring, its been previously clipped, the gearbox internals are completely stock with the exception of the spring. So you recommend I get a new battery and replace my new G&P M120 motor that I got yesterday. As well as putting the m120 spring back into the gearbox and short stroking the sector gear and piston?

[North West Outpost]

Re: G&P M4 double firing and locking on semi.

No I wouldn't do that now.

Keep the parts you have with maybe the exception of the spring. A short week spring will not help with over run. I would get either an M90 or M100 which ever gives you your target fps.

If you are looking to upgrade the gear box, how would you want it set up? What would you want it to do?

[dave38x]

Re: G&P M4 double firing and locking on semi.

The G&P M120 is (as i have discovered through two guns im working on at the mo) quite a nippy bit of kit when combined with an m120 spring and a short stroked 13:1 gearset

[North West Outpost]

Re: G&P M4 double firing and locking on semi.

But no where near as nippy as a Neo Ultra torque one with an 11.1....

[dave38x]

Re: G&P M4 double firing and locking on semi.

Indeed - on a 7.4 i've got an shs HT with that gearbox to 25rps, the m120 pushes that closer to 30

[SunSpectre]

Re: G&P M4 double firing and locking on semi.

I am achieving 22 rps off of the current set up. And I'm quite happy with how it is and I'm not looking to upgrade, all I want done is the issue of semi auto solved. I'd hate to have to put in my stock SRC motor just so semi works well enough for indoor fields. So I think I will get a better spring, as I have a systema hop up unit and a prometheus barrel, i'd like to think that an m90 would give me 300-330 without any clipping required.

[North West Outpost]

Re: G&P M4 double firing and locking on semi.

New spring it is then.

If you are able to tweak internals you should now know what you have to do

If you do, do not forget to remove the corresponding teeth from the rear of the piston and correct AOE. Or it is bound to end in tears.