Slide to Glock is sticking

So my friend gave me his Glock to fix. Every time you to fire it the slide sticks. It's been cleaned and it still is jamming. Anyone have any ideas?

Sticking in what way? Mine did the same thing. Does it stick on the way back and leak gas?

Don't know about the gas leaking, but I'd assume so. But yeah it's sticking all the way back.

Is it sliding like its supposed to? As in, is it able to glide or does it have a stick to it like theres sand in it?

It cocks normally the first time, but after you fire it once the slide stays back. What I do to push the slide back in is turn the safety off (seems to catch the slide each shot) and then pull back like I'm cocking it again.

Is this a KWA GBB?

The "empty" mag indicator may be messed up. Most blow backs have a mechinism that locks the slide back when the last round is fired. It is located where the mag meets the chamber. It may be messed up causing the slide release to lock.

It's a KJW one

And Auto how do I check it to see if it is working?

There is usually a tab on the side of the mag where the bb's feed. The Tab comes in contact with the slide release when the last shot is fired.
I would pull the slide off and reinstall everything except the slide. Insert an empty mag to see where the tab hits to lock the slide.
Than I would load a few BB's into the mag and reinsert it to see what happens with everything.
You may also notice something out of alignment with the chamber nozzle and it may be making contact with the BB feed tip on the mag.
Do this with the slide off to see if anything jumps out at you.
After that, reinstall the slide and look in through the mag well to see where everything is fitting and rack the slide a few times.

I had the same problem with a ksc Glock 26c.

What i ended up doing was taking the slide off and GENTELY sand or file down the guide parts the slide.. slides on.. Normally you will see a little wear taking pait off the guides inside it. File them down a little bit lube em, then try it. took a few trys but it doesnt get stuck back like theres 10 pounds of sand in there anymore.
Mine functions Like a dream now.
It used to get cought up on the ejector cover deal. Where on the real steal the shell ejects out