barrel cap it the thing on end of the barrel, two, i know stock hop up for ca m24 will, but it is an upgrade that works for aps2 as well
Stock barrel length for a CA M24 is 515mm. The closest you'll find is 509mm (M16 length) without having one custom cut for you.
A APS II PDI hop up will not fit in a CA M24, it isn't wide enough for the barrel. PDI does make a M24 hop up, which is damn near impossible to find, without ordering direct from the source. It will support an AEG barrel, as does the stock CA hop up. However, it is well worth the hunt to procure a PDI chamber for your M24.
Also, you will not find a barrel cap specifically for an M24, unless you can find it somewhere second hand. An APS barrel cap will fit, and you should be able to find it at some overseas retailers, but they're not quite the same size, so it's going to look out of place.
CA M24's need a lot of upgrades to be a reliable sniping implement. But once you get them up to scratch they are very nice. I almost bought one but didn't have the money at the time. I've wanted one for a looooong time. Pretty much since I was introduced to airsoft. If I come into a lot of money randomly it's quite high on the list of things I'd buy.
Jump, does the gas cylinder leak like crazy? You were talking about it on SEMIA
It worked great at first, but it's made pretty shoddy. There are some sharp edges along the sides where some screws are set, and they started to bend upwards and snag on the reciever after time. I filed them down which helped, but then the whole damn thing started warping, then leaking. It worked great when it was new, but after time it just turned to crap. It wasn't the internals, it was just the build quality of the bolt itself.