How to Get the Most From an AEP Gearbox?

[HuttArmouries]

Im currently looking at building an m1 carbine based around an aep gearbox. Im mainly looking at these gearboxes because I have stacks of them for spare parts and other bits and it is small enough for me to keep real m1 carbine dimensions. Im looking to get around 250-300fps out of the 18 inch barrel though I may cut down the inner barrel a bit if it proves to be too long. Ive repaired a lot of aeps but never really looked into upgrading them. What parts to people recommend?

 

[Rogerborg]

The usual route is an Eagle6 M80 spring: https://eagle6.co.uk/shop/catalog/product/view/id/206/s/eagle6-airsoft-upgrade-spring-for-aep-cmg-series/

However, it's an absolute sod to fit - you really will want a third hand - and under serious compression even with the piston right forward.  I've tried it full length, and I've tried it with some coils lopped off, and got pretty much exactly the same 240fps both ways.

The inherent problem is that the cylinder is just so small.  I'd expect an 18" barrel to be counter-productive and you'll want to use a shorter one.

The other issue on the pistol systems (dunno about the SMGs) is, as you'll have seen, the nozzle mechanism.  The air enters the nozzle from the bottom, and the nozzle is sealed at the back by an o-ring on the guide pin, but I'm suspicious about both of these seals.  I've tried pushing another o-ring inside the back of the nozzle to give the guide pin o-ring a greased rubber surface to seal against, but it didn't help.  I peak out at 240fps regardless of spring or seal.  Maybe I need a longer barrel, but again, there's very little volume to exploit.

Eagle6's claim of getting 300fps out of an AEP... well, I'd love to know what else was done to it.  0.37J vs 0.83J is a huge increase.

 

[HuttArmouries]

The usual route is an Eagle6 M80 spring: https://eagle6.co.uk/shop/catalog/product/view/id/206/s/eagle6-airsoft-upgrade-spring-for-aep-cmg-series/

However, it's an absolute sod to fit - you really will want a third hand - and under serious compression even with the piston right forward.  I've tried it full length, and I've tried it with some coils lopped off, and got pretty much exactly the same 240fps both ways.

The inherent problem is that the cylinder is just so small.  I'd expect an 18" barrel to be counter-productive and you'll want to use a shorter one.

The other issue on the pistol systems (dunno about the SMGs) is, as you'll have seen, the nozzle mechanism.  The air enters the nozzle from the bottom, and the nozzle is sealed at the back by an o-ring on the guide pin, but I'm suspicious about both of these seals.  I've tried pushing another o-ring inside the back of the nozzle to give the guide pin o-ring a greased rubber surface to seal against, but it didn't help.  I peak out at 240fps regardless of spring or seal.  Maybe I need a longer barrel, but again, there's very little volume to exploit.

Eagle6's claim of getting 300fps out of an AEP... well, I'd love to know what else was done to it.  0.37J vs 0.83J is a huge increase.

Click to shrink...

Thanks. ill have a look at that. I will be converting the aep to have an inline nozzle and use mp5 nozzles so hopefully that should give a better airseal if done right. 

 

[Rogerborg]

I will be converting the aep to have an inline nozzle

Click to shrink...

Now, that'll be interesting to see.

 

[Samurai]

I gave up on mine too, because whatever I did, I couldn't get it above 240fps either. I've changed all O rings to better sealing ones and re-shimmed, re-lubed it.

I even printed a nozzle that's closed on the inside with a shorter nozzle guide. Also changed the O rings and maximized the seal on the factory one as much as I could. No difference. Neither with the Eagle6 M80 spring.

I've made about 8 different springs from vsr springs with different lengths and power. Still 240, even when the motor could barely fire it.

I have the one with the updated barrel and hopup rubber that are almost VSR compatible. But they aren't so I couldn't change those.

 

[Rogerborg]

I even printed a nozzle that's closed on the inside with a shorter nozzle guide.

Click to shrink...

Now that's dedication. I was pondering sealing off the back of the nozzle and shortening the guide, but it sounds like it's not worth it.  I reckon it's just limited by the small cylinder volume available.

So I've given up trying for more than 240, and am back to a cut-down M80, mosfet and 1200mAh 7.4V lipo, which just (barely) fits after cutting a hole in the receiver under the barrel and pushing it in from the front.  Along with a heated-and-weakened trigger spring, the trigger response is vastly improved over stock and that's what I care about in CQB.  It's getting dressed up as a las-pistol anyway, so is just for LARP-larks.