Start with chamber brush and CLP by hand to make sure you have the chamber cleaned of grease and debris to start with.
Also, have you tried another upper on the lower to make sure the problem is not the lower not built correctly/having the problem isntead.

Now,
Pull the bolt off the carrier, and dry fit the carrier with key to the upper.

Carrier should move freely in the upper, and gas tube should be aligned with key.

Step two, put the B/C back together, CLP around the back of the key to the carrier top, then hold the bolt in while using 100lbs of air to pressurize the front of the key, to make sure that you don't have an air leak between the bottom of the key to top of carrier.

From here, you don't state if FSB or gas block, but we can pressure check either as well.   Piece of rubber hose on the end of the gas tube in the upper receiver, CLP around the front and back of gas block to the barrel, and around the key to gas block, then use the hose with air compressor blow gun next to take the gas tube up to 100lbs of air pressure.

As for ammo, if you are shooting steel case ammo, or some low powered import ammo, verse brass case USA produced ammo, the problem could be the ammo.  So rigs have a hell of a time with steel case ammo until the chamber has self polished in with live fire and cleaning (500 rounds) until the chamber is smooth enough to cycle the steel case ammo.

As for lube, should be using CLP to not only clean the rifle, but to lube is as well.  The only thing that we don't clean on the rifle with CLP is the bore, and here we use something like Sweets copper solvent that will clean the copper fouling quickly, and will not leave behind a residue that does not mix well with CLP.

Again, clean and lube the rifle with CLP.

CLP for the most part is not the liquid in the mix that is the lube, but the PTFE teflon suspended in the mix that is the lube instead.

Also, the reason that the military switch over to CLP from LSA as a lube for the M16 platform, is CLP as lube for the rifle has a wide range of temperature use for the rifle; including sub zero temps as well. Also, CLP has a cleaning agent in it, and anything that you missed during the cleaning, the use of CLP as lube will dissolve the fouling that you missed/tries to build up during live fire as well.

If you need a source for CLP, the large spray cans of BreakfreeCLP is the ticket for less than gallon quantities.


If you have have a source to buy from GSA to get the discount, then ROYCO 634E price is cheaper by the gallon or more  instead.
https://qclubricants.com/royco/royco_634.htm

Being ZERO degrees might be a major contributing factor.

You mention that you cleaned and lubed the rifle, with what lube and where?  Also can you tell us what ammunition you were using?

When teaching Armorer Courses, we try to get the point across that you need to look at the AR15 Weapons System as a high performance engine.  Most high performance engines will do best when using a high octane fuel and lubricant.

For process of elimination, as already mentioned, I would suggest trying some quality made ammunition from a reputable manufacturer like Federal, Speer, Black Hills, Hornady, Remington, Winchester, etc.  I would also suggest that you try some .223 and 5.56 ammunition, there is a major difference in gas pressures, and see if you get any difference in cycling.

You mention that you were shooting in ZERO Degrees, this may be the root of the problem or at least a possible contributing factor.  For process of elimination try a different lubricant than what you may be using.  We are based out of Minnesota, where it is cold 5-6 months a year, many days below zero degrees, which CLP doesn't perform well for us (especially at 20F or colder, as it gums up, causing short stroking).

For lubricants I prefer Slip2000 "EWL" Extreme Weapons Lube, and "EWL30", Slip2000 has NSN Numbers as they are issued to the US Military.  In Armorer Courses we teach to use the "EWL" for all around lubrication and rust protection, as it flows nicely into all the little crevices and holes, reduces friction greatly, and protects very well from rust. The "EWL30" is what I put where I need a lube to stick and not run, places like handgun rails, roller bearings on M14/M1A/M1 rifles, etc. The "EWL" I have used at -37F, and I have also used the "EWL30" at -34F, and both performed well. I am based in MN, and we need gun lubricants that perform in sub-zero temps. The "EWL" has also performed well when running instructor courses in San Antonio when its 125F, and it doesn't burn off even when shooting lots of full auto.

Here is a little info on the Slip2000 "EWL" Extreme Weapons Lube:

http://www.slip2000.com/blog/side-by-side-review-of-slip-2000-ewl-and-clp/

http://www.slip2000.com/blog/ewl-vs-clp-testing-greg-sullivan-comments/

http://www.slip2000.com/blog/colt-with-15000-rounds/

SWAT Magazine article: Filthy 14, BCM Rifle Goes 31,165rds on Slip2000 EWL

http://www.slip2000.com/blog/169-infantry-thanks-slip-2000/

http://www.slip2000.com/blog/pat-rogers-8000-round-letter/

As for where to lube:
The bolt carrier has rails that it rides on, if you are behind the gun shooting it, the gas key is located up at 12:00, and the rails of the bolt carrier that it rides on are located a 2, 4, 8, 10 O-clock, and the big flat spot on the bottom of the bolt carrier is at 6:00 where the bolt carrier rubs as it travels rearward during the hammer being recocked, all of these surfaces do best with a light coat of lube so it is glistening like a glazed donut.  If you drop just the bolt carrier (No bolt, cam pin, firing pin or retaining pin) into the upper, you will see that it slides in/out of the upper receiver with almost no resistance, as it rides on the rails as already mentioned.

If you insert the complete bolt carrier assembly (Bolt carrier, bolt, cam pin, firing pin & retaining pin) into the upper, and move it in/out you will see that the bolt carrier still rides on its rails with very little friction, but you will find that the largest friction is from the 7 bolt lugs rotating to lock/unlock with the barrel extension (7 barrel lugs).  Once you get a few rounds on the rifle, you will see where metal rubs metal on the 7 bolt lugs, where you see signs of metal rubbing metal is an indicator of where you need lube.  So the 7 bolt lugs need to be lubed wet, imho you cannot get them too wet, they at least need to be glistening wet like a glazed donut, so for process of elimination on your next range trip I would suggest soaking them with lube.

CY6
Greg Sullivan "Sully"
SLR15 Rifles
TheDefensiveEdge.com
(763) 712-0123