My CZ-75 started locking its slide open 1/2 way through a clip. I will be shooting and the slide will lock open like the mag is empty but there will still be rounds in the mag. I'll move the slide release and the slide closes and everything is fine.

Another problem is sometimes the slide does not close all the way. The slide stops about an 1/8" from full closure. Most of the time I just push on the slide and it closes up.

Any ideas. Most of the ammo I shoot is reloads. The gun has had about 1000 rounds through it. Both problems happen with new ammo but not as much. The gun has been cleaned. Also the problem does not happen as much when my friend shot it.

Quoted: Also the problem does not happen as much when my friend shot it.

It doesnt like you...
give it to me. I never met a gun that didnt like me.

Usually stuff like that is caused by magazine problems. Often times by the mag spring. Dissasemble the magazine and stretch out the mag spring a little to give it more power (only a temperary solution). Clean the mag very well and test the gun. Test the gun with a different mag. If that fixes the problem replace the mag spring.

Given a good firearm with good mags and ammo, most "gun" problems are actually "shooter" problems. The two clues here are that you are mostly shooting reloads and that the gun does not do it as often when your friend shoots it. I would first clean the gun and all mags (do not stretch the springs) making very certain to clean as well as possible the area in and around the extractor, breech face and the chamber, then lube and reassemble. Check to be certain the mag springs are replaced correctly...high end toward the front of magazine...and use almost no lube inside the mag body (I put a little on my fingers and rub it on the spring...that's all) If these are aftermarket mags, get some factory made ones.

Next, get some good quality brass case factory new ball ammo and try the pistol out. My guess is that it will run like a sewing machine. Factory hollowpoints, too, should work fine, but it is remotely possible that certain bullet designs could bump the slide catch on the way up and cause the slide to lock back with a partial loaded magazine. More likely you are bumping it with your support thumb, so watch your grip. Also, the slide not always going fully forward could be: dirty chamber, breech face and/or extractor area; improperly resized reloads; or the shooter "breaking the wrist" when shooting. While this most often shows up as a failure to eject, a heavy, reliable 9mm like the CZ may also occasionally barely get the case ejected, but not quite have enough energy to complete the "feed" and "lock" stages of the cycle of operation.

Try this and see if your problems don't disappear. (and tell the reloader to use a taper-crimp die and jacketed bullets)

Could it be that your thumb is riding the slide stop while the gun is cycling?  This could lock the slide back and it could cause enough resistance to keep the the action from locking.  I had this happen a few time to me with my Glock.

Try changing slide stop spring. Friend of mine committed same problem with his Tanfoglio Limited custom. He changed CZs slide stop spring and gone were the problems.

MN