Gear Review: The KynSHOT Hydraulic AR Buffer

I’m a weird gun enjoyer and subject matter enthusiast when it comes to retro ARs. Specifically, I like weird retro ARs. When H&R released the DOE SMG clone, I knew I had to have one. Officially, Colt called this the 633, and it served in minimal numbers with the Department of Energy.

Many folks don’t know that Colt also made the 633HB. HB stands for hydraulic buffer. Colt couldn’t get the buffers to work reliably back then, but after nearly four decades, someone had to do it, right? Yep…a company called KynSHOT has mastered it.

As an H&R DOE SMG owner, I wanted to make it into a 633HB. My gun has a 7.5-inch barrel and is a 9mm straight blowback gun. KynSHOT makes specific buffers for specific guns. The 5.56 hydraulic buffer doesn’t work well in a 9mm straight blowback gun, so it’s smart to be exact.

Very specific

Down to the barrel length specific. Luckily, they have an easy menu system to be sure you get what you want. My buffer is the KynSHOT RB5007, which works with my particular firearm setup. I contacted KynSHOT, and they sent me a buffer to make my dream of a 633HB come true. KynSHOT makes some big claims about their buffers. They say they can reduce felt recoil by 30%.

A short, straight blowback 9mm has what many consider a fairly violent recoil impulse. The DOE SMG clone features a blade-type brace, and if one were to somehow inadvertently misuse their brace and place it against their shoulder, they’d realize the term ‘blade’ is pretty accurate. Even when firing with the proper use of the brace, they’d quickly find the gun fairly difficult to control.

There is no reason a 9mm PCC should have the same recoil impulse as a 5.56 rifle. The KynSHOT hydraulic buffer seemed to promise it doesn’t have to. I’m not an AR expert, but I’d be willing to bet that straight blowback PCCs would benefit more from these hydraulic buffers than just about any other gun.

How Does A Hydraulic Buffer Work?

The idea is pretty simple. The hydraulic buffer has a piston. When the weapon fires and the bolt moves rearward, the piston is compressed into the buffer. Instead of a spring, the hydraulic fluid in the buffer dampens the movement of the piston as the bolt drives rearward.

When the bolt carrier group reaches its rearmost position after firing, the buffer presses it forward. The hydraulic fluid also controls the forward movement, which gives it a buttery smooth bolt return.

The downside of these buffers has always been their hydraulic fluid. If the buffer leaks, it’s useless. If it’s too cold or hot, it won’t work. KynSHOT’s made their buffers extremely durable, and like anything, they might eventually break, but it will take some real effort. It’s made from 17-4 stainless steel and rated for full-auto fire.

The hydraulic buffer can work in temperatures ranging from -30 degrees F to 150 degrees F. This particular model weighs six ounces and is 4.35 inches long. It’s longer than most, and with the DOE SMG, I had to remove the polymer spacer from the bottom of the buffer spring.

Does This Thing Work?

Installing is simply a matter of switching the buffers. There isn’t much to it. Prior to doing that, I ran a few magazines of 9mm through my DOE SMG using the standard buffer. I then ran a couple of drills and recorded the times. I did the basic Bill Drill, the Failure To Stop, and some basic double and triple taps.

After that, I tossed the KynSHOT buffer in and shot the same drills. In every drill, my times were slightly better. The most significant difference was in the Bill Drill. I got it from 1.9 seconds to 1.75 seconds. That’s a slight improvement but a noticeable one.

The KynSHOT buffer noticeably reduces felt recoil, which is apparent after the first shot is fired. While that’s great for comfort, when it comes to performance, the real kicker is how fast the sights return to the target. They move less and come right back down, allowing for those fast follow-up shots.

The difference between the KynSHOT hydraulic and standard buffers is night and day. I noticed the difference between my straight blowback and 9mm from the first shot. It makes the gun much more pleasant to shoot. I love shooting the DOE SMG, so this is icing on the cake.

With this combo, I’ve dialed in several hundred rounds, and there have been zero problems. It runs just as reliably as the gun previously did and runs a fair bit softer now.

Worth the Squeeze

The KynSHOT buffer has a retail price of around $100. It’s not a cheap upgrade and probably not one many would make to plinkers. However, this might be the way to go if you want an edge in your next PCC match. It helps with faster recovery and shot times and time is money, or at least it’s points.