I just took my second AR out for it's first test drive and the bolt would not lock back when the mag was empty. I also cannot get the bolt to lock back when I depress the bolt catch. I am a rookie at gunsmithing, I need some ideas at what to look for or look at. Thanks!

Does the bolt catch move at all on an empty mag (while locking bolt to rear)?

How about with you pushing on it (no mag)?

Repeat with upper removed - compare results.

YF,

Do you mean the bolt doesn't lock to the rear when you pull the bolt back and press in on the bottom of the bolt catch? Or do you mean that when you fire it with the bolt catch pressed in the bolt does not lock back?

If it's the first then something is getting in the way of the bolt or buffer, like too long a buttstock screw.

If it's the second then you have a short stroke.

The bolt catch only needs enough tension to keep it in the down position while the bolt cycles during firing, any extra is wasted.

Just a thought...

The teeth on the end of the bolt have to get behind the bolt catch.  If the stock screw is too long, it can prevent the buffer/carrier/bolt from going all the way back.

The answer to both of tweak's questions is yes. I can not get the bolt to lock back no matter how I try it.

What is a short stroke and how do I fix it?

I will try changing the buttstock screw.

So in essence, you are saying that the bolt will not retract back far enough into the receiver for the bolt lugs to get behind the bolt catch, when pulling back all the way on the charging handle, right?  If this is the case, there is something in your buffer tube that is keeping the buffer from moving all the way to the rear.  If this is a A1 buttstock, the problem could be you have an A2 buttstock screw installed.  If it is an A2 buttstock, then I would be surprised to find out the screw it too long, but I guess it could be a possibility.

Do this, break apart the upper and lower, remove the buffer and buffer spring and see if you can find anything wrong with the inside of the buffer tube that would keep the buffer from moving all the way back.  Compare the lower, carrier, and bolt to your other AR and see if you can find anything that is different, that could obstruct full movement of the carrier.

As far as short stroking goes, refer to it as short recoil, or Chuck will get on your ass and make you feel like an idiot.  Short recoil/stroking can be caused by all sorts of things and can be very hard to diagnose and cure.  Basically, it is caused by either the gas system not getting enough gas to the carrier to push the carrier/bolt all the way back, or from something rubbing against or obstructing the full movement of the carrier.  Would need a lot more info to diagnose what is causing the short recoil issues, like ammo used, brand and model of rifle, etc.  That said, if I am correct in my initial assesment at the top of my post, then I doubt it is a short recoil issue.

Thanks for all the help guys! The problem was the buttstock screw was too long. I think what happened was I bought a GG&G single point sling adapter and it came with a longer screw to make up for the adapter and spacer included. Again thanks for the help guys; I don't thiunk I would have come up with that solution on my own.