Okay, so.....
If another atty (the RM4) fires on the reo fine, then it's not your button cover (which sometimes restricts the action of the button and firing pin). It's also not the 510 connector on the reo.
If the atty reads consistently on an ohm reader (one with a 510 connector), then you should have a good build and the atty should be capable of firing.
That would seem to leave the 510 connector on the reo - as in, the atty is not making a good connection with it. The atty center pin might be a tad short (hard to tell from the pic), but I still suspect that the atty is not screwing in enough to make contact. I have a cyclone that screws in tight on two reos but not far enough to make contact, yet screws all the way in on another and works fine. All other atties work great on all those same reos.
Now, I've not adjusted the center pin on those particular atties, so I'll bow out of advice on trying that - Filthy Beast is most likely your man there. If it is a threading issue, maybe PM'ing Rob (redeyedancer) would get you some good advice.