Did you know that all AR-15 and AR-10 bolt carriers tilt down at the rear end as the action cycles? This phenomenon called “carrier tilt” became widely known when piston driven ARs became popular because in some cases it was severe enough to cause obvious damage to the gun in short order. On the piston guns, the gas piston strikes the solid carrier key on top of the bolt carrier to drive it to the rear. This strike at the top of the carrier causes the lower, rear of the carrier to tilt downward as it starts to move which makes it contact the lower portion of the buffer tube (receiver extension). On most standard bolt carriers, the rear of the carrier is completely unsupported and there is enough play in the tolerances between the carrier guide rails at the front and the upper receiver to allow this movement. So a lot of piston guns were getting noticeable wear in the buffer tube or at the front edge of the buffer tube after just a few hundred rounds and customers didn’t like this. To fix the problem, piston gun manufacturers enlarged the profile of the rear end of the carriers and beveled them or machined “skids” into them so they couldn’t tilt as far and if they did impact the buffer tube, the wear wouldn’t be as significant. This is a partial solution for the piston guns, but some tilt may still happen depending on the tolerances and there is a bit of movement before the carrier gets inside the buffer tube where the skids can help.
What most AR shooters don’t realize is that the Direct Impingement Guns or “Gas Guns” also suffer from some carrier tilt. It usually isn’t as much so it may not result in any buffer tube wear or other obvious visual signs. But the gas still hits the carrier at the top, just as it does on a piston gun causing the rear to tilt. It’s impact just isn’t as abrupt as a piston is, so the tilt isn’t normally as severe. But there is still the same amount of play in the carrier to receiver fit to allow for tilt on a gas gun and it still can have negative consequences even if it isn’t damaging your buffer tube. When the carrier tilts as it starts moving to the rear and unlocking the bolt, it is putting extra stress on the bolt which is still locked into the barrel trying to turn and pull through the locking lugs. This stress can eventually cause the bolt to crack and break, normally at the locking lugs or at the cam pin hole, which are two of the thinnest and most stressed points on the bolt. So that’s a serious problem right? If your bolt breaks, your weapon is down hard until it can be replaced.
So how do we solve this problem? The piston gun manufacturers modified the design of the rear end of the carrier as mentioned above. That’s a good thing. Many shooters carry a spare bolt in their pistol grip which is a prudent idea in case one does break. Some of the top tier companies started making their bolts out of tougher steels and doing more quality control on the bolts which raised the price a bit, but is a good thing for the gun owner and does reduce breakage. But in my mind, a real solution needs to get rid of the carrier tilt in the first place and remove these stresses from the operating system altogether. That’s where the anti-tilt buffer comes in. An anti-tilt buffer has a protrusion at its front end that extends into the hole in the rear of the bolt carrier. It supports the bolt carrier through it’s entire cycle not allowing it to tilt more than a few thousandths of an inch. So the buffer tube doesn’t get any wear, the bolt doesn’t endure any stresses from the carrier tilt and the entire system cycles more smoothly because there is less friction. All in all this is a great solution. As you should know, there’s always a trade off somewhere for these advantages, so what’s the down side of an anti-tilt buffer? Since the buffer is holding onto the rear of the carrier, you can’t just pull the rear takedown pin and shotgun open the action. You have to pull both the rear and the front takedown pins and pull the upper receiver completely off of the lower receiver to open the action. Not too bad right? Some folks don’t like this because they are so used to opening up the action that way, but it’s a pretty small trade off for a smoother running, longer lasting operating system if you ask me. Besides, now days you can find all sorts of easy pull take down pins to make pulling them both a breeze. So if you want the smoothest running, longest lasting operating system you can have take a close look at some anti-tilt buffers. The CTS Aktive buffers are some of the best.