Saturday, July 05, 2008

Guns: Your Gas Key & You (A Public Service Announcement)

Just after iffy magazines and broken extractors, the carrier key is probably the most common source of AR malfunctions. I speak from personal experience - my first Bushmaster ran like a top for about a thousand rounds, but then it mysteriously began to short stroke, sometimes badly enough that the bolt stripped off chunks of brass from the top round in the mag instead of shucking it into the chamber.

What is the carrier key? It's that little part on top of the bolt carrier than hooks right into the gas tube (it's also called the "gas key" for that reason). Hot gases from the propulsion of the bullet down the barrel get bled into the tube, and the resulting pressure pushes the whole affair back, cycling the action. If the key is loose or misaligned, however, gas leaks out and the bolt carrier isn't driven back far enough, resulting in a failure to eject (or worse) a short stroke that completely brings down the gun.

The carrier key is fixed on there by screws, but as any engineer will tell you, screws tend to come loose, especially when we're talking about environments that are as hot as an oven and undergo hard, repeated mechanical shocks. The popular carbine length gas systems also send the bolt back in a much harsher fashion than the relaxed rifle length systems, exacerbating the problem. There is a way to keep the key from working loose, though - stake them.

The idea behind staking the carrier key is simple. Just whack enough metal from the key into the screwhead, and the blasted thing won't move. But very few companies do it right nowadays, for whatever reason. Before you trust any AR with your life, please check the gas key and make sure the screws aren't going anywhere. If they aren't staked right, use a center punch and hammer and stake 'em yourself. I'm not sure why AR makers keep screwing this up, though. To be frank, it borders on negligence -if the key comes loose at the wrong time, your fancy AR becomes a magazine-fed straight-pull bolt action rifle. If it comes loose at a truly wrong time, you might lose your life.


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