Ditto, since smoke is lube/grease burning off from the heat.

My guess, when building the parts on the PSA, did not first CLP clean the parts to remove any grease on it, and its the storage/assembly grease that is burning off.  Think moly lube for the barrel nut, and even initial parkerizing oil/ storage grease on the barrel parts so it does not rust before it sold.

Hence CLP will also burn off as well, but since it a thinner layer, it burns off pretty quick, while grease on the other hand, smokes a lot longer for the time it takes to burn off.

Visual lingering gas smoke is lube burning.  So if it boils down to the lower, douse it with CLP (clp has a cleaning agent in it), then use compressed air to blow all the lube out of it.  Also make sure to pull the buffer and spring, to clean them and the inside of the tube. Hence lower too lubed will migrate the lube to the upper parts, and could be the reason for the smoke.


If the problem is a quick blast of smoke as you fire the rig that dissipates quickly (not lube burning off), then could be that the bolt is unlocking a touch too fast  and your seeing the action gas instead.

With lower cleaned/blow out as pointed out above, if the lower is one with telescoping stock, then swap the buffer/recoil spring/charging handle on it it, from an another carbine lower that does not have the same smoke problem,  to see if they solve the problem.