I've got a second hand 1911 that I've test fired a couple of times with Abbey Ultra, however the slide doesn't lock back on the last shot. Is this likely to be because Abbey isn't powerful enough and it needs green? The mechanism is all there and it locks back if I slide it back, but just not when the pistol is fired.
Some of my pistols often don't do that... My WE is one of them... It doesn't do it on Propane either.
Generally I just don't worry about it.
give it a good lube. try it on green. if it still doesnt work dont worry 
it dosent afect the function of your pistol in my expirience it is not enought presure whit the gas field strip it and clean it, lub it and try on green gas
I could be an a luftwaffe ace you know?..........................................................................Die Unsichtbare Waffe!
Cheers guys, I'll give it a clean and lube later on and see how it goes.
Hi WhosWill?.
Dunno if you've solved your problem yet, but even if you have I hope the following might help other WE'ers with similar troubles.
I've a number of WE gassers in my collection and in my experience this is not an unusual problem with both 1911's and Hi-Cappa's. It's usually down to one of four problems (or a combination of 'em).
1. The mag follower spring is too weak to push the holdback catch up far enough to latch the slide back. Push out the pin holding the top bb guide from the mag (left to right viewed from behind the mag) and gently streach the spring a little. Not too much or you'll make it worse 'cos the spring will loose it's temper (No, it won't get the hump!) 
Try and stretch every turn of the spring a little, rather than make one or two big stretches.
2. The mag follower and/or the moulded channel it runs in is a bit rough.
A gentle smoothing with it bit of fine wet or dry paper wrapped around a matchstick solves this.
3. On Hi-cappa's sometimes the little projection on the front of the mag follower which stops it rising up too far prevents the follower from pushing the hold back latch high enough. Using a sharp scalpel cut a tiny sliver off the top and try it again. Only cut the tiniest amount each time and try out the mag before cutting more.
On 1911's you need to file away a little of the plastic on the BB guide where the mag follower stop hits it.
4. There's a little "nib" formed on the hold back latch which is supposed to prevent the latch rising whilst the gun is in use which is sometimes a bit too pronounced and stops the latch being pushed up by the mag follower.
I generally give the "nib" a gentle filing to flatten it a bit and allow it to ride over the latch spring rod. Again, take a little at a time and keep trying it out. If you end up removing too much of the the nib there's nothing to prevent the latch rising when the gun is in use.
I'd try each of these in turn before doing the next 'cos each is a little more destructive than the last.
I'm not a great lover of lube around mag followers, it usually only attracts grit which makes the problem worse. If, as is the case with WE mags, the follower is plastic then it's self lubricating and shouldn't really need oil or grease.
Remember though, WE spares are VERY hard to come by and usually bloody expensive even if you can find someone to sell 'em to you, so do BE CAREFUL...
Good Luck. 
Forgot to say, all WE's are designed to be used with Green gas as standard. Abbey Ultra ain't man enough.
Happy Days.
