Bulk fill adaptor without Cap (Front screw caps sold out, I can bore out you standard front cap if required), with inlet valve  to prevent the air coming out, for the XS/TH or QB 78 so you can bulk fill with Co2, or even air. It is best to use Co2 so that you get quit a lot of shots. The trouble with air is that you don't get many shots. If you use air then you must not exceed around 950 PSI pressure. Although you don't get many shots, you can get more power so check the power after fitting if running on air, then set the power to be below the legal limit if required, this will then increase the number of shots when using Air. This will give you more shots. Set so that the gun cannot exceed the legal limit of your country.
 This can be used with our longer reservoir to get more shots, as it has double the capacity.

Check where your relief hole is at the end of your reservoir, to make sure the O ring is positioned back enough to block it. They varied the hole position on the later ones and these had a longer front cap.

If you have the type that needs the O ring nearer the rear then you can sometimes get away with putting one or more O rings on the smaller Outside  diameter behind the O ring.

Please note, that these only fit the 78 and 501 models, not 79