first shot always misfeeds
 

Ares G36:

There are no BBs in the gun. I put in a mag, and the first shot misfeeds, no BB. All other shots after the first shot, fires fine, no double feeds, misfeeds.

I've ruled out the hop-up, magazine, by putting in another gearbox. It fires fine with the replacement gearbox.

Does anyone have any idea what might be wrong in the gearbox?

Thanks.

If it's always the first shot after a mag is inserted that mis feeds, it's not an issue. There's no bbs loaded into the hop up chamber when the mag is inserted because the nozzle is forward. After the first shot, the nozzle retracts and a bb is now loaded. If you're lucky, the nozzle is retracted when you insert a mag which will allow a bb to be loaded. There's nothing wrong with the gun.

Yep, that's totally normal, although, I haven't experienced that problem since I installed an AWS raptor mosfet in my gun! :P

Put a full mag in shoot a few rnds off then do a mag change (without having emptying first mag), now with fresh mag take one shot, if a bb comes out and doesnt missfeed then it means that the gears are stopping in an overclocked state.(means that on trigger pull guns doing over a full cycle causing the tappet to be pulled back while the mags empty and doesnt load a round on next shoot as the loading part of the cycle was completed on an empty mag). If this isnt the case then theres something else.

It isnt uncommon but can cause you issues in a game when you might realy need that first round.

Er, when the spring isn't under tension, the nozzle should be all the way forward. The sector gear doesn't release the tappet plate until after the piston has started retracting. If your gun loads a shot after it fires, it means your mechbox is stopping mid-cycle. End-of-cycle should be tappet plate and piston fully forward. Ie, no BB loaded.

Looks like you guys are right.
At the end of cycle, the nozzle is sitting a little too much forward. There is not enough gap between the air nozzle and the hop-up bucking for a BB to fit in between. So when I put in a mag, the BB is prevented from being pushed in front of the Nozzle and the hop-up bucking.

Comparing my new gearbox and the old gearbox, the difference in the nozzle position is like 1-2 mm.

An active braking mosfet would remedy this.