One of my “grail guns” has always been the Kel-Tec SU-16D9 SBR. This is, as grail guns go, a bit of an oddity. It’s cheap. It doesn’t have a sterling reputation. The after-market is almost nil.

But what it does bring to the table is a piston-operated 5.56 carbine that weighs almost exactly 5lbs with optic, muzzle device, and decent stock. I know this is not as impressive as it once was in this era of $2500 4lb titanium/carbon-fiber AR-15s, but for one fifth the price, it’s still a pretty stunning accomplishment.

I have never seen a proper end-user review of the Kel-Tec SU-16D9, so I am very pleased to bring you this one!

I have no previous experience with the PLR-16 or SU-16 rifles. I did previously own a SU-22, but sold it after discovering how much I hated the field strip and reassembly procedure.

The SU-16 series (or “SU16” – Kel-Tec uses the terminology interchangeably) are Kel-Tec’s line of light-weight, polymer receiver 5.56×45 rifles. They take AR mags, and have a variety of handguard and stock configurations. My understanding is that the SU-16CA is rather popular in ban states due to being cheap and “featureless”. There is also a “pistol” version called the PLR-16 which lacks a stock. The SU-16D9 is a mash-up of the SU-16C’s lower receiver and the PLR-16’s upper receiver.

I bought the SU-16D9 off Gunbroker for about $500. Since this is an SBR, transfer took about ten months. I could have done a form 1 on a PLR-16 and saved some time, but overall cost would have been very similar, and going with the SU-16D9 means I retain the factory warranty – no small consideration with any rifle, in my opinion.

The rifle comes in a plain, Kel-Tec branded box with the SU-16C folding stock, a sight adjustment tool, and a manual. I swapped the stock out at the transferring FFL with the SU-16E collapsing stock assembly in order to stay on the right side of MD’s rifle OAL floor limit law. I configured the stock assembly with the Vltor A5 buffer tube (no buffer assembly) and an MFT Minimalist stock. This very comfortably meets the 29″ mark. On the downside, it adds about 6oz over the folding stock assembly.

The first thing you notice about the rifle is how light it is! In this era of 8lb AR-15s, a 5.56×45 rifle that’s 5lbs with optic and irons feels feather-weight. The rifle, as you see it configured in the pictures in this article, is 5lbs 1oz with optic, and a bit under 5lbs without the optic. The balance of the rifle is front-heavy, with the center of balance being right in front of the receiver. If keeping weight as low as possible were not a driving consideration, I think you could improve balance substantially by weighting the rear of the rifle with a heavier stock. However, the charm of the SU16-D9 is in its light weight, so I don’t recommend that. It is entirely usable in the configuration shown.

The gun is designed around a clamshell upper/lower receiver paradigm, with a serialized upper. The polymer receivers are interchangeable in the SU-16 and PLR-16 lines, so you could theoretically swap in a SU-16A/B/C lower receiver if you wanted a more traditional-looking stock. As mentioned before, it comes with a “C” style stock out of the box, but that was not going to work for me legally due to MD’s overall length floor.

Ergonomics are usable, but not optimal. I really like the pistol grip – there are no finger grooves, and the angle is similar to the A2 pistol grip. The texturing gives you a bit more grip, but it’s not exactly a custom stippling job. It’s a good thing I liked it, because it’s molded into the stock assembly (which is essentially a lower receiver for the gun) and cannot be changed. I’m surprised they didn’t just allow the user to bring their own AR pistol grips, but I assume this was manufacturing optimization.

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The safety is a cross-bolt, and it’s not in a great spot for turning it on and off quickly. If I could change only one thing about the gun, this would be my pick. An AR-style safety would have been vastly more intuitive and faster when using the pistol grip AR-style stock. I understand why they’ve got this style of safety – it’s parts commonality with the other SU-16 models which have traditional-style stocks – but it is not my preference over the AR-style.

The charging handle is right-hand-only, reciprocating, and not switchable. The D9 model has the upgraded “deflector” charging handle which is supposed to act as a shell deflector.  If you like living that AK/Sig 556/etc. life, this will be right up your alley. I found myself wishing it could be put it on the left hand side, because you’re going to be racking it every time you do a magazine change on a locked bolt.

Yes, that’s right – this gun has no bolt release. It does have a bolt-hold-open which is conveniently located right behind the magazine well. You simply rack the bolt back and push up on the bolt hold open. I think if you were handy with a dremel and tap that you could create a cut-out in the receiver (and threaded hole in the bolt-hold-open) to manually actuate it, ala the RFB. As it is, you will be racking that charging handle to get your gun running after it locks back on an empty mag.

The handguard in the front of the gun is… meh. It has a bottom picatinny rail, and no provisions for attaching accessories (like a weaponlight) to the sides. The gas tube is left completely exposed, so C-clamping is out. This probably would have been acceptable 15 years ago, but it feels lacking nowadays. Despite being a little ugly, it’s not uncomfortable to hold, especially with a minimalist rail cover on the bottom rail.

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There are after-market handguards that provide you with side and top rails. Red Lion Precision makes one, and so does Midwest Industries. The problem with both is that you’re dumping a bunch of weight into your lightweight gun. I’d rather just accept that this is my light-weight funsies/hiking rifle and live without those additional rails for now.

The magazine release is positioned nicely for righties, and is a good size. There is no provision I could see for switching it around for lefties. The spring is maybe a touch heavier than I’d prefer, but no big deal.

In summary, it’s usable, but not amazing. I’d love to see a Gen2 release that fixes some of these issues, but I suspect it’s a ways off. When I talked to Kel-Tec at SHOT earlier this year, they claimed no immediate plans for the line.

We’ve discussed how the SU-16D9 feels. But how does it work?

The SU-16’s operating system can be broadly described as “rotating bolt locking using a long piston and a recoil spring around the piston”. This is pretty standard stuff, very similar to the Sig 556. The gas is not adjustable. You can get a suppressor piston that will reduce the amount of gas going into your gun, but the gun will not operate unsuppressed when using that piston. Given the horror stories I’ve read online about the PLR-16 beating itself to death when running suppressed with the wrong piston, I made the decision that I’d rather just not bother, especially on an NFA item.

The barrel is 9″ long, chrome-lined, and has a 1:9 twist. I would have preferred 1:8, but realistically, 1:9 is fine for the kind of shooting I need to do with this rifle. If the Rifle Shooter Blog’s numbers carry over to this gun, I should expect about 2600fps when using M193 ammo. You cannot depend on fragmentation with that sort of velocity, so you might consider using different ammunition that relies on expansion instead if terminal effects are something you consider important. Personally, the only things I shoot are paper and steel, so this isn’t much of a concern.

The gun feeds from AR mags. It does not seem very finicky as to the sorts of AR mags it will accept, which isn’t always something I take for granted.

The factory muzzle device is an A2 flash hider. There is nothing wrong with this per se, but it’s a somewhat uninspiring choice. I replaced it with a VG6 Epsilon combo device. The Epsilon is rather similar to the Gamma, except that the Epsilon replaces the third blast chamber in the Gamma with flash hider prongs. The gun uses what seems to be a thin lock nut to keep the muzzle device in proper orientation. It works properly, but I would recommend some Rocksett to make sure things stay in place over sustained use. Ordinarily, I would not use a brake of any sort on a gun this short, but the gun’s extremely light weight makes a brake more appealing as a recoil-reduction mechanism. I might experiment with putting a VG6 CAGE on it in the future.

Field stripping is not exactly intuitive, but isn’t terribly difficult once you get the hang of it. You push a pin to allow the upper and lower halves of the gun to clamshell open (exactly as you would do on an AR), twist the gas tube 1/4 of a turn, retract the bolt, pull out the bolt handle, and then pull the BCG (with long piston) assembly out the bottom of the top half of the gun. That is as far as most people will need to go. You can push a couple more pins if you need to disassemble the BCG and piston. The two halves on my gun are rather tight and require some force to separate, but I assume they’ll break in over time.

To operate the gun, you slap in a fresh mag, rack the charging handle, push the safety through, and then pull the trigger. Trigger pull could be described as mediocre verging on bad. Think “kinda heavy mil-spec AR trigger” with just a little bit of flex due to the plastic trigger. It’s not the worst pull out there, but it does leave you wanting more, and would get in the way of precision shots at longer ranges, not that you should be doing 600yd shooting with a gun this short. If the flex bothers you enough, people do make metal triggers that you can fix that problem with.

The sights are usable, but that’s about the best I can say for them. They’re very low, and the rear peep aperture is smaller than I’d like. My irons came more or less zeroed – I had to tweak the windage to get them a few inches to the left, but this is a common issue for me on most rifles.

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The front sight is on the gas block, and is essentially an AR front sight, with elevation that adjusts in the same manner. The rear sight is a peep sight. It’s the special metal model specific to the D-series of SU-16s that has protective ears around the peep sight. The windage adjustment is… ugly. The rear sight has two screws, one on each side, and each quarter turn gives you 1.3 MOA of adjustment. Problem is, you’ve got to turn both screws to do it, which is not exactly a friendly mechanism. Oddly the adjustment screws on mine were broken out of the box – you could get a screwdriver into them, but they clearly had damage. Someone at the factory got a little too ambitious with a power screwdriver, I guess. If you hate the rear sight, you do have the option of using Tech Sights, which are not cheap and add weight, but do provide you a quality AR-style rear sight.

The easiest solution to the so-so iron sights is to simply use a reflex sight as your primary sighting system. The best options are a pistol-style MRDS like the RMR, or an Aimpoint Micro-style red dot. I had recently replaced the Romeo4M on my class rifle with a Romeo6T, so the Romeo4M seemed like the clear choice.

The iron sights are low enough that co-witness is not a very viable option. I went with QD instead, and bought a used LaRue LT661 mount. The LT661 put the Romeo4M pretty low, and provides the option to remove it quickly in case of failure. It is very comfortable to use with a normal cheek weld, and the circle-dot reticle is far faster to use than the iron sights. The only thing I didn’t love is that the LT661 is not the lightest mount in the world… but some things are worth spending a couple ounces on, and an outstanding QD mount is one of them.

In actual use, the light weight of the gun makes handling phenomenal. It comes up to the cheek with shocking speed, and it just feels like a gun you could carry all day. I’d also attribute some of that to the MFT Minimalist stock. This is the first time I’ve used it on a rifle and I am extremely impressed by it. They packed a lot of features into a very light-weight stock, and the shape of the buttpad really lends itself to how I shoot (closer to my center line than my shoulder pocket).

At this point, I am sure many readers have two questions:

1. How bad is the recoil with a gun that’s so light weight?
2. How bad is the concussion with the Epsilon combo muzzle device?

I am pleased to say that recoil isn’t bad, especially with the Epsilon muzzle device. There is substantial concussion, but it’s tolerable. The 9″ barrel doesn’t seem all that much longer than the 7.5″ standard you see on many AR pistols, but that extra 1.5″ of barrel does seem to reduce blast down to much more reasonable levels. (Mind you, reasonable is relative, but I wasn’t getting the evil eye from bystanders on the range.) One thing I noticed was that ammo selection seemed to make a real difference in the perceived flash. Wolf Gold was not all that bright, but the Wolf steel-case was exceptionally flashy.

I was able to shoot it relatively fast and accurate – thanks to the VG6 Epsilon – but the handguard’s short length was not conducive to getting a really solid grip. Even if you wanted to C-clamp it close in, the piston tube gets hot under rapid-fire, and is not a comfortable place to put your hand without some heat-resistant gloves. I might try putting an AFG or VFG on it in the future to provide some more hand purchase.

Accuracy was… OK? I’d estimate about 2 MOA with the Wolf Gold I tested it with. This is a close-range SBR, so I don’t have huge expectations in terms of accuracy. Bullets went about where I wanted them to, which is pretty much all I expect on a gun like this.

One early problem I ran into was that the muzzle brake came loose and started rotating. Kel-Tec seems to want use to use a lock/jam nut to keep your brake in place, and the lack of room between the handguard and the muzzle device makes it hard to get that jam nut right where you want it. I took another stab at tightening things up and used Rocksett, and this seemed to fix the problem.

Reliability was 100% for the full time I tested it, including mags full of cheap steel-cased ammo. I used Magpul M2 and M3 pmags, and a GI-style C Products magazine. No obvious difference in functionality with either.

Is this rifle worth $800, including the tax stamp and transfer? Probably not for most people, at least not in this current incarnation. It really depends on what you’re trying to do. If you want a ultra-durable, high performance rifle, forget it, this is not the gun you’re after. If you want a very light-weight, affordable SBR in 5.56 that can fit in relatively small places, this might be more up your alley – especially if you’re not in MD and can use the factory folding stock to further reduce weight and footprint. If you’re into the backpack/carrier bag carry thing (RIP SBS) and don’t go out of state often, this could be just the ticket.

Configuring the SU-16D9 is a bit of a game of compromises. Putting a VFG and an optic on there add weight, but they also add capability. What about a side-folding AR stock mechanism? Is putting another 6oz on the gun worth having a side folder? These are hard questions for a gun that’s this light weight.

Now, if you don’t feel like paying the NFA tax, the SU-16E is really only a bit heavier than this rifle (.2lbs), and has most of the same advantages and disadvantages. I personally like SBRs, so I went the SU-16D9 route, but the SU-16E is a perfectly reasonable option.

I’d really encourage Kel-Tec to invest a little more engineering time into the SU-16 platform. An MLOK handguard that covers the gas tube would add a lot of utility, and a tweak to the “E-style” lower receiver to give it a short-throw selector would make it much more ergonomic. If we’re really wish-listing, some tweaks to the gas system to allow it to operate suppressed or unsuppressed without swapping parts would also be greatly appreciated.