Introducing the ayatollah of lock-and-rollah! DMM has had their kick-butt Revolver wiregate pulley carabiner out for a few years now and it has proven itself in the field. See that review for how to put together an ultralight crevasse rescue hauling system. Now our fine Welsh friends have done it again, this time with lockability.
Available in three different locking formats, climbers will want the screwgate. The action on the screwgate is buttah smooth, and unlike the wiregate it's a keylock nose for snag-free unclipping. The screwgate adds minimally to weight for a total of 2.2oz. The gate opening is a little tight but workable at 16mm.
The Revolver is fully certified as both a carabiner and as a pulley. The pulley makes wandering ropelines pull smoothly for less leader effort, and the ease of lowering saves wear on your 'spensive thread for top-roping. If you're still wandering the icefields with old-school pulleys, do yourself a big favor and chamber some Revolvers.