Why is my AR short-stroking in cold weather?
Just got back from a range day at about 25°F and my AR started failing to fully cycle after about 40 rounds — bolt not locking back on empty, sometimes short-stroking on live rounds. It's a 16" carbine-gas PSA upper, H2 buffer, standard BCG. Warm weather it runs great. What should I check?
- @ben.rourke8h agoAccepted0
Cold-weather short-stroking on a 5.56 carbine-gas gun is usually one of three things, in order of likelihood:
**1. Lubrication is too thick.** Most gun oils thicken meaningfully below freezing. If you're running something like CLP, try switching to a cold-weather lube (Slip 2000 EWL, FireClean, or just a lighter oil like Lucas Extreme Duty for the winter). The BCG should look wet, not filmed.
**2. The gas port is marginal.** PSA uppers are fine but have slightly more port-size variance than premium uppers. Cold-weather gas pressure drops, so an under-gassed gun that runs fine at 70°F may stall at 25°F. Check by running it with a lighter buffer — H1 or even a carbine buffer — and seeing if the cycling issue goes away. If it does, your gun is marginal on gas and the H2 is masking it until weather changes.
**3. Ammunition.** Cheaper 5.56/223 loads run at the lower end of the pressure window and get worse in the cold. Try a known-hot load like M193 surplus or 77gr match — if those cycle and cheap 55gr softpoints don't, your ammo is the issue.
Most AR-15 cold-weather issues are the lube. Start there.
- @caliber.club8h ago0
Seconding the lube point. I ran into exactly this two winters ago at a mountain match and the fix was as simple as switching off CLP. Cold-rated gun oils are a real thing.
One other thing to check: your BCG gas rings. If the rings are worn (you can check by pulling the bolt forward from the carrier and seeing if it stays extended on its own — it should), you have marginal gas sealing, and cold weather will push a marginal gun over the edge.