I have a problem with my glock.
 

When ever in full automatic mode, my glock 18c never shoots the last shot. The slide remains back while 1 more bb is still at the top of the mag. Is this normal or abnormal?

Not normal but maybe a simple problem. The slide lock mechanism is very simple. On the mag there is a little tab that is connected to the bb pusher that catches onto the slide lock bar. When there are several bb's in the mag the tab is slid downward and away from the slide lock. As bb's are consumed the tab slides upward until at the end of the bb's it contacts the slide lock bar, pushing it up and against the slide (locking it back).

It sounds like from your description that the slide lock bar is catching when there is 1 bb in the mag.

First try another mag, if the problem still occurs then check the slide lock bar mechanism. Take off the slide and load a mag with several bb's. The slide lock bar should not lift up. Try with no bb's, it should lift up. Try with 1 bb, if the slide lock bar still lifts up then it is catching too soon and you may be able to file the bottom tab (be careful) enough for this to not happen.

Be careful, personally I'd just live with the last bb problem it sounds like everything else works.

Reference:

Slide lock bar is part # 66 & 67 on this diagram --> http://tech.airsoftcanada.com/KSC/ksc-g18cs.jpg

The little tab on the right hand side of yours is probably bent downward a little and catching sooner then later.

i did what you said and w/ 1 bb it does not lift w/ zero bbs it lifts. but whenever i fire it in full auto the slide locks while 1 bb is still in the mag.

there is probably not enough gas int eh mag to make the slide go all the way back. most probably from yoru mags freezing up on you. try this .. fire full auto about 10 shots, wait a couple minutes, fire off 10 more shots, wait a couple minutes, then fire the rest.

if i'm right then the slide should lock back after all the ammo is gone. by a couple of minutes I actually mean use your watch and count 3 minutes. you can even take he mag out of yoru gun and hold it in your hand to warm it up a bit faster

kk ill just wait for it to warm up. But why do you think the slide locks up while 1 bb is still in the mag? isnt it supposed to lock after there is no more ammo.?

Next time that happens, try to see what is causing the slide to lock back. Is it the tab on the mag lifting the slide catch up even though there is still a bb left, or is it something more sinister.

The problem is, the tab on the mag lifting the slide catch up even though there is still a bb left in the mag.

Does the BB follower looked damaged in any way? Is may cause the BB to be recessed more into the magazine in which case it won't load once the follower reaches the top and engages the slide catch.

Or, does the groove where the tab comes through the BB lip to engage the slide catch look damaged?

Does the problem occur with every mag you have?

What happens if you pull the slide back when it locks open? Does the mag catch drop down and allow the slide to chamber the last pellet?

yes it chambers the last slide. And I see no damage to anypart of the mag, the tab, or the bb lib that chambers the bb.