Best guess, the wrong buffer in play, the B/C is not coming back far enough, and the catch is only catching the bottom of the carrier; not raising up in front of the bolt isntead.

Pull all the way back on the charging handle, and the face of the bolt should stop about 1/4" to 1/8" in front of the back of the ejection port, but behind the bolt catch. Also, on the last inch'ish of the pull, the charging hand tension should be about the same as from half way back (and not harder instead the last inch)

If you have the correct buffer and recoil spring length in play and the above it correct, then next shotgun the upper open, and insert a empty mag.  The follower should raise the bolt catch all the way up, and if this is not happening (catch not binding in it receiver slot and the problem at hand), then you may have to pull the bolt catch to check the catch spring channel for debris that you may have missed when the catch spring and buffer was installed).

Lastly, what stock on the rifle, since if you have an A-1 or after market stock that uses a butt stock screw, could be that the butt stock screw it too long, and now protruding into the back of the receiver tube to block the buffer from coming all the way back isntead.

Make sure you got the stock kit for the AR10/SR25, not the 223; and then make sure that you used the butt stock screw that came with the kit!!!!!

http://www.semperfiarms.com/store/product/stocks-pistol-grips/TN-PRSInstall.pdf

If the above it correct, the start checking the bolt catch install itself.
Does the bolt catch move freely in the receiver slot for it (just has the spring tension pulling it back down), and does a empty mag raise the bolt catch all the way up ( no debris in the catch spring channel that are causing the catch spring to over tension and not allow an empty mag to raise it all the way up).



It you are still good, then single load a round into a mag and fire for effect.  If the bolt is not locking back, then the rifle is short stroking, and now time to double check the head spacing*, gas system for leaks or blocks, and no FCG binding*.

* Armalite 308 carrier will not work with the wider DPMS/Stoner type hammers, and you have to use a DPMS/Stoner chamber barrel with a DPMS/Stoner type bolt. If you are mix matching a DPMS/Stoner bolt with an Armalite chambered barrel (or visa versa), your head space will be off (too short, or too long).