I built my mech cocker myself and played around with QEVs. Although I did eventually get it shooting nicely (much like your slider), I ran into the same problem you're having.
I'm pretty sure its that your lug isn't catching on the sear. The reason it cocks and fires when not gassed up is that when you cycle it by hand, you're doing it much more slowly than when the ram does it. The sear simply isn't coming back up fast enough to catch the hammer as it blows past. The QEVs certainly aren't helping.
I'd remove the QEV on the front of the ram. If that doesn't fix it, lower the lug and re-time it. If that still doesn't fix it, use a stiffer sear spring. Lastly, flat-topped lugs work better than round ones for mechs simply because they seem to catch better than rounded ones.