Hello, I just got done putting together my first AR . RRA lower with a CMT upper from Del-ton (service was excellent). I have not gotten the chance to shoot it yet but am wondering if the bolt is supposed to lock back when an empty Mag is seated, or if it actually requires the force of firing the last round to lock back the  bolt. I appreciate any help and advice you guys can give.

The bolt will not jump to the rear if you insert an empty mag if that is what you are asking.  If you have an empty mag and pull the bolt to the rear, it will lock.  If you are firing to an empty mag, it will lock.

Thanks for the response. When I insert an empty mag, and pull the charging handle, my bolt does not lock back. Do I have a problem?? Thanks

Yes. The bolt should lock back with an empty mag. If it does not lock back either the Mag follower is faulty or there is something wrong with the bolt hold open itself. If the bolt stays open when you use the bolt hold open button, then the problem is most likely the magazine.

Only use USGI mags.

Best of luck.

The mags are all brand new USGi with magpull followers and ranger plates. I have 3 of them and none of them lock back the bolt.

When I pull back the charging handle I can feel it start to catch on the bolt relese but it does not stop and continues forward. Thanks for all your help

Remove the upper (with hammer cocked and safety in the SAFE" position), then insert an empty magazine. It should be obvious how the BHO is supposed to work, and relatively simple to see what is going wrong.

If the BHO does not move freely against its own spring pressure, then likely there is a bur or dimensional mismatch between the BHO and the lower receiver. If the mag follower does not engage the BHO properly, it could be the followers, the mag or the mag catch position (does the weapon feed ammo reliably from the mags ?). If everyhting works OK in the lower/mags, look to where the BHO engages the bolt to confirm the engagement is good.

try pulling the charging handle back while pressing on the bolt hold open manually.  if it doesn't work like that, there's something wrong w/ it.

When all else fails, consult the -23&P

1) Magazine follower worn or broken (not likely)
2) Magazine catch spring worn or broken (not likely)
3) Magazine follower binds (not likely)
4) Broken Bolt Catch and/or Spring (you did install the spring and follower right?  And lube them?)
5) Restricted movement of bolt catch (remove, clean & lube).

Thanks for all your help I am going to dissasemble it and see what I can find in a couple of hours. I will report back.

The bolt catch should bounce freely on the tension of the bolt catch spring.  You don't need to disassemble anything to check this, Cleatus.

I'm assuming you know how to manually engage the bolt catch with your support hand Military Style?

Does this process work?

Are you a COD DP?

Unfortunately I am a total virgin to this AR stuff. No, I am not sure how to manually engage the bolt stop military style?? And I am not even sure what a DOP Dc is?????

Quoted: I am not sure how to manually engage the bolt stop military style?? ??

Don't worry about 'military style'.

Just wrap your left hand's fingers aroudn the mag well and depress the lower (smaller thin protrusion) portion of the bolt catch while you pull the charging handle all the way to the rear with your right hand.

But with the bolt foward you can check function just by depressing the lower portion of the catch as MarkM indicated.  It should return back as soon as your thumb comes off the bolt catch.

Well, I think I found the problem but I need your guys input. Here is a picture of the bolt carrier, it looks as if the machining is off a bit and there is a side slope where the carrier makest contact with the BOH. Is this normal??? The BOH looks perfect and is definitely installed correctly. Thanks for all the help.

http://i6.photobucket.com/albums/y209/bgriggs/DSCN0630.jpg

The sloping ramp on the front of the bolt carrier appears to be  machined correct.

This is not what the bolt catch locks back against.

The bolt catch locks back against the face of the bolt, specifically the bottom two lugs.

The problem could be that you are not pulling the bolt back far enough to completely clear the bolt catch.

Pull back on the charging handle as far as you can get it to go with an empty mag seated or while depressing the bottom (under the pivot point) of the bolt release lever on the left side of the weapon as when aiming.

When you look into the action while the bolt is properly locked back you should see the bolt catch protruding up in front of the bolt inhibiting it's forward motion.

If you do not see this the bolt is not properly locked back.

It is possible, on some especially new guns, to have the bolt actually "lock/hold" in the rearward position and not be locked.  The bolt catch usually grabs that ramp on the carrier and not the bolt, but it will slam shut with slight jostling.  

Quoted: Pull back on the charging handle as far as you can get it to go with an empty mag seated...

+1

What stock are you using? If it is a fixed stock, it is possible to have too long a screw in the buttstock, which would prevent the bolt carrier from going fully to the rear.

Quoted: Quoted: Pull back on the charging handle as far as you can get it to go with an empty mag seated... +1 What stock are you using? If it is a fixed stock, it is possible to have too long a screw in the buttstock, which would prevent the bolt carrier from going fully to the rear.

This is my guess also. A too long screw holding the buttstock to the buffer tube will keep the buffer from retracting fully and wont allow the blot to stay open.  I had this exact problem with my DPMS RACE GUN and didnt know what was up with it until I found out that one of my teammates had the same problem on his rifle.  

I cannot get the bolt to lock back. if I pull on the charging handle while pushing in the bottom of the BOH it will hold for a split second but then slam forward. I cant determine if it is the carrier if the BOH. The stock is an ACe socom. Thanks for all the help.

Quoted: The bolt catch locks back against the face of the bolt, specifically the bottom two lugs.

Alright after looking into the action as I pull back the charging handle the bottom 2 lugs clear the bolt catch but they just barely make contact. If I press the bottom of the bolt catch the bolt will stay back for a second but then slide over the bolt catch.?????????????