I acquired the T3 receiver and trigger assembly, shown below, for $500. The beautifully machined bolt and receiver are proprietary, but everything else is compatible with the broad market of Ruger 10/22 accessories. The trigger assembly features a crisp 2.5-pound trigger, and is all metal except for the trigger itself and the convenient extended magazine release lever in front of the trigger guard.

I installed the receiver in a Hogue stock. The 18″ barrel came muzzle-threaded from EABCO and button rifled with a 1:9 twist rate: sufficient to stabilize subsonic 60gr Aguila .22 bullets. (The standard .22LR twist rate is 1:16.) Those two components brought total cost for the gun to $750, excluding a scope.

My goal with this rifle was to make it as quiet and accurate as possible. As I have previously explained, “quiet” firearms are created by:

1. Adding a suppressor to the muzzle to catch as much of the supersonic propellant gases as possible
2. Keeping bullet velocity below the sound barrier, thus avoiding the distinctive “crack” of a supersonic object
3. Selecting an action that avoids venting propellant gas under pressure other than through the suppressed muzzle

I already had a registered Gem-Tech Outback II — a light and competent .22 suppressor. There are plenty of subsonic factory loads for .22LR, including most target ammunition, so the second requirement was easy. To ensure the third requirement was met I knew I wanted a manual action, since especially with the shorter cases of 60gr .22LR bullets there is a risk an autoloader will extract the case while there is still enough pressure in the barrel to create an audible pop out of the chamber. (Note: I have since read that with the right combination of bolt handles and recoil springs a semi-auto 10/22 can be kept closed long enough that there’s no pop from the ejection cycle. Given that $500 can also buy a complete Volquartsen or KIDD receiver/bolt/trigger assembly I’m inclined to try making that work next time.)

As for accuracy: In principle manual actions are also the most accurate, since the gun doesn’t have to do anything to cycle the action before the bullet leaves the muzzle — things that could introduce variance from shot to shot. In practice, however, it seems that especially blow-back autoloaders in small calibers like .22LR can be made as accurate as all but the most finely tuned manual loaders. Nevertheless, I decided to remove that variable and build a gun with a manual action.

The most common manual action rifle is the bolt-action. (Lever- and pump-actions are also not uncommon, but I’m not aware of any that allow such easy customization as bolt guns, and since I wanted a precision barrel with an unusual twist rate I knew I would have to assemble my own gun.) I have a number of bolt-guns, including a .22, and it always struck me as overkill — like using a sledge hammer to push a thumbtack — to be using a camming bolt (or “turn-bolt”) on such a low-pressure round. So I started looking for “toggle” actions.

Straight-pull bolt actions are rarely seen outside of olympic biathlon shooting. They offer a slight speed advantage over turn-bolts, which require the shooter to rotate the bolt at least 60 degrees in and out of battery before it can be pushed and pulled to feed and extract a cartridge from the chamber. But toggles and straight-pulls do require a more complicated mechanism, so perhaps that explains their near-total absence from any niche where bolt actions aren’t required and fractions of a second don’t matter. (There are a few notable exceptions: The Blaser R93 and the Merkel RX Helix are high-end centerfire rifles with straight-pull actions.)

All I could find for toggle .22′s were Russian Izhmash rifles (customized for biathlon and running upwards of $1500) and a line by Browning called the T-Bolt (but not readily equipped with the fast-twist barrel I needed). Then PWS came out with their T3 rifle patterned on the Ruger 10/22, so I jumped on it.

Review

To date I have only tested this gun with Aguila subsonic ammunition — both 40gr and 60gr. When I first assembled it I had frequent failures to extract. PWS techs instructed me to file down the extraction groove of the barrel and that solved that problem. Then I had frequent failures to eject: The extractors would just drop the case before it hit the ejector, and even if it made it to the ejector more often than not it would fail to be kicked out the ejection port. This was a trickier problem. After some research the PWS techs concluded that the rim on Aguila 60gr .22LR is .269″ where a standard 22LR is .274″. They machined a primary extractor to account for the difference, but installing it didn’t completely eliminate the problem.

What did make things run reliably was to cycle the bolt quickly (which one should do anyway). This helped mitigate the other quirk of this toggle action, which is that the bolt runs into resistance at the rear of the stroke where it has to cock the trigger. You have to give up your grip on the trigger to cycle this thing, but if you just tug on it with two fingers and follow through to the rear of the stroke it runs back and forth smoothly.

I will cover accuracy results in an upcoming post.

RAT WORX made the clever design decision to build this upgrade around a standard AR-15 trigger group, which they suggest will allow users to tap the extensive market for AR-15 parts to further customize it. I just put it right in my MSAR and took it for testing.

Trigger weight measured a very consistent 6 pounds. Nominally that doesn’t sound any better than what I found with the Trigger Tamer. But practically there is no comparison: the HTM’s all-metal linkage from the trigger bar through to the sear and hammer eliminates sticking and stacking I couldn’t polish or lubricate out of any previous trigger systems. With this trigger I finally feel confident shooting my MSAR against standard AR-15s. With a 4x optic my test group was able to consistently ring a 200-yard steel silhouette shooting at rates up to 5 rounds per second.

Expanding subsonic rifle bullets: Right now there are no commercial .30-caliber rifle bullets that expand at subsonic velocities. AAC/Remington have promised they will introduce one this year. I hope they’re not the only one. After .22LR .30-caliber cartridges are the next stop for subsonic rifles — whether .300 BLK, 7.62 Thumper, or .308 Winchester. The problem is that rifle bullets have traditionally been designed for terminal effect at rifle velocities: Much below Mach 1.5 and they don’t expand at all. At 1000 fps they can virtually have the rifling marks polished out and be reused!

Gun powder for consistent subsonic rifle loads: Trailboss is the current go-to powder for subsonics, but it doesn’t produce consistent muzzle velocities and, at less than 5 grains per cc, is too bulky for some cartridges. The only other option in this range of burn-rates is IMR SR 4759, but its density jumps to 10gr/cc and consequently doesn’t produce very consistent muzzle velocities at reduced loadings. There is nothing on the market to bridge the gap between the two. Give us a powder with a burn rate roughly in line with SR4759 but a density around 7gr/cc.

High-speed consumer video cameras: When Casio came out with the F1 in 2008 I was hopeful that it would not be long before consumers would be able to buy sensitive video cameras capable of recording 480p at thousands of frames per second. The technology is certainly there to produce such a product in scale for under $1000. However Casio discontinued its nascent consumer HSV product line in 2009 and nobody has pursued this since. The market is now free for the taking!

Reasons to get a .22LR conversion for your semi-auto pistol:

• Cheap ammo allows for more practice ($.03-.05/round vs $.15-.30/round)
• Low recoil helps inexperienced shooters acquire good shooting habits and experienced shooters to verify they haven’t developed bad trigger habits
• Semi-auto malfunctions are still encountered — in fact, far more frequently than with the standard gun, which is actually a positive since it gives the user more practice correcting them
• Suppressors don’t require booster devices because the .22 conversions are all blow-back actions

Advantage Arms has had a Glock .22 conversion kit on the market for years. But they never offered a threaded barrel, and for me the ability to shoot suppressed in my back yard was a big draw. This year Tactical Solutions came out with a conversion kit that is available with a threaded barrel, so that’s the one I bought. I paid $350 for the kit, but what they did not make clear (at least when I bought it) is that their slide does not come with sights. So add $40-90 for another set of sights!

This picture shows my original Glock 17 slide. The .22 conversion is just a replacement slide, shown underneath without and with my suppressor attached. Weight and balance of this conversion are kept pretty close to the original:

• G17 slide is 17.2 ounces and its center of balance is 3 3/8″ from rear
• TSG slide is 13.3 ounces and its center of balance is 3 3/4″ from rear
• TSG with Outback suppressor weights 16.6 ounces with center of balance 5 1/8″ from rear

The other piece of the .22 conversion is a magazine. A fully loaded G17 mag weighs about 10 ounces. The TSG magazines can hold up to 15 rounds, but they weigh only 4 ounces loaded and protrude from the bottom of the grip by about half an inch. The magazines are one of the big shortcomings of this conversion kit, and not just due to their careless proportions: I bought an extra mag, and even after sending everything back to Tactical Solutions and shooting at least 1000 rounds through it the conversion will stovepipe virtually every round it tries to feed from a mag containing more than 10 rounds.

The other big drawback to this conversion, which it shares with seemingly every other .22 semi-auto on the market, is that full take-down for cleaning requires undoing screws. In this case, two tiny screws that are very difficult to reseat and very prone to galling. You can’t even fully remove the barrel without doing a complete take-down. And as with anything that eats .22 ammo, things get very dirty. But you can probably clean enough to keep it running just by scrubbing the feed ramp, bore, breech face, and extractor.

The final serious problem with this conversion, which is common to all other rimfire guns, is that dry firing can eventually break it: Rimfire rounds “fire” when the firing pin crushes the case rim (which contains the primer compound) against the chamber rim. Dry-firing causes the firing pin to directly strike the chamber rim, gradually denting the “anvil” needed to support a round’s rim during firing. In theory perhaps the firing pin could be made of a metal sufficiently soft relative to the chamber that it couldn’t dent it no matter how many times it hit. But in practice I was able to observe cratering beginning after just a handful of dry strikes. This is particularly problematic because the Glock is designed to be dry-fired before take-down. If you’re careful it is possible to dry-fire for disassembly while holding the slide slightly off the barrel so the firing-pin doesn’t hit it. But even if you are diligent in that you will probably inadvertently dry-fire many times during shooting because it doesn’t reliably lock the slide back on an empty magazine.

Bearing these issues in mind, I was reasonably satisfied overall with the conversion kit. As this photo shows the gun is capable of more accuracy than most people can wring from open sights on a standard-length pistol. Tactical Solutions recommends shooting either Federal AutoMatch or CCI Mini-Mag HV ammo (both of which shoot about 1050fps with a suppressor, which is only marginally subsonic but still quiet enough to not bother the neighbors) for maximum reliability. Granted, “reliability” for a .22 semi-auto is relative: Even without loading more than 10 rounds I count myself lucky if I make it through a magazine or two of AutoMatch without a failure to feed. But that’s part of the practice, and with .22s I can afford to practice a lot more.

This is an XCR semi-automatic rifle in 7.62 Thumper. Shown is the “mini” upper with a 10″ barrel and AAC’s Cyclone suppressor. This is an awesome firearm that offers the power and accuracy of a rifle with the option of using subsonic loads that are not only hearing-safe but which “won’t wake the neighbors.”

In the following video I shoot a ten-round magazine of subsonic 220gr bullets. These leave the muzzle at 1000fps, which means they carry 500 foot-pounds of energy — comparable to a .357 magnum at point blank range, and greater than a .45 ACP pistol. And because they are very long, ballistically efficient rifle bullets they retain 80% of their energy out to 300 yards, which is roughly the outer limit of being able to accurately place a subsonic bullet.

Like most, I began my quest for subsonic rifles shortly after buying my first rifle suppressor (a.k.a. silencer). After all, it was cool to be able to shoot without hearing protection, but supersonic bullets make a loud and unmistakeable sonic crack of their own. The only way to further suppress a rifle’s noise is to shoot the bullet below the speed of sound.

What is 7.62 Thumper?

In principle it might seem easy to slow down a bullet: just put less powder behind it, right? However a number of undesirable things begin to happen as you do this with a given cartridge: First, as you continue to reduce the powder charge below roughly 80% you will begin to get increasingly inconsistent muzzle velocities, which dramatically reduces the gun’s accuracy. Drop the charge even further and you occasionally get a bullet stuck in the barrel, sometimes accompanied by a potentially catastrophic phenomenon often called “secondary explosive effect” which has destroyed many guns! Also, since a bullet’s energy equals mass times velocity squared you will be severely weakening your bullet’s power as you slow it down. To solve these problems you soon realize that what you want is to shoot a much heavier bullet. But as I explained in a previous post the only practical way to make a bullet heavier is to make it longer. And longer bullets combined with slower muzzle velocities require faster barrel rifling to get spin-stabilized enough to shoot straight. Before long you will realize that if you’re going to build a subsonic rifle capable of producing appreciably more energy than a .22LR it’s going to need at least a .30-caliber bore.

7.62 Thumper is one of a number of specifications for short rifle cartridges designed to shoot .30″ bullets at subsonic velocities. A host of proprietary and wildcat cartridges have existed for this purpose for decades, like the .300 Whisper and .300-221. However various drawbacks have prevented them from being widely adopted. The attraction of 7.62 Thumper is that it uses a standardized and widely-available case and chamber: 7.62x39mm Russian, which is the standard caliber for AK-47s. Peter Cronhelm posted a fair amount of research on subsonic shooting with the 7.62x39mm from bolt guns. My goal was to start with that and work up a gun and load that would shoot standard 7.62x39mm rounds but also reliably cycle subsonic rounds in a semi-automatic rifle.

The heaviest standard .30-caliber bullets are 240gr, which require a barrel rifled with a 1:8 twist to stabilize at subsonic velocities. Since no standard .30-caliber barrel has such a fast twist a new barrel is going to be part of any subsonic conversion. And this is why we make the distinction between 7.62 Thumper and 7.62x39mm: Russian bullets are .311″ diameter, whereas the only widely-available .30-caliber bullets heavier than 200gr are .308″. In theory you can shoot .311″ and .308″ bullets in either bore diameter, but I have tried that and the effects tend to be either bad accuracy in the case of undersized bullets or else shredded jackets and exploding bullets in the case of Wolf Military ammo in the high-twist .308″ bore. So a 7.62 Thumper gun is 7.62x39mm chamber but a .308″ bore with a 1:8 twist rate, and it’s best fired with .308″ bullets.

What about .300 AAC Blackout?

Halfway through my development of this rifle the Freedom Group announced its own solution to the same objective: the now SAAMI-standard .300 BLK caliber, which is designed specifically to work on the AR-15 platform. The ballistics are virtually identical to 7.62x39mm, and as with 7.62 Thumper a standard rifle only requires a new 1:8-twist .308″ barrel to shoot accurate subsonic loads. The advantages of .300 BLK are (1) It uses the small .223Rem bolt standard on AR-15 rifles instead of the large 7.62x39mm bolt standard on AK-47s, and (2) Remington will be producing factory subsonic ammunition, whereas you still have to load your own 7.62 Thumper ammo.

Why the XCR?

Getting a 7.62x39mm to shoot 220gr subsonic would be easy enough. But getting it to cycle a semi-auto action was unknown territory. I knew that I wanted a piston-driven semi-auto with an easily-modified gas system.

Given that I wanted to work with 7.62x39mm AR-15s with their small bolt were immediately ruled out. I also knew that I would potentially be yanking and changing a lot of barrels to get this to work. Fortunately, my favorite tactical rifle, the XCR, met the bill. The XCR’s barrel goes in and out with a single screw. The XCR also has one of the best piston gas systems for tuning: From the factory it comes with 5 hand-adjustable settings. And if those don’t work it’s easy to remove the regulator and gas block to enlarge holes to increase pressure.

The machinists at Robinson Armament, maker of the XCR, were also willing to build some custom barrels for this project at a reasonable price. I sent them a Shilen stainless steel barrel blank bored to .308″ with 1:8 twist cut rifling. RA cut it in half and put it on their machines to turn out the two drop-in short barrels shown here: 10″ for the shorter “mini” XCR upper, and 12″ for the standard-length upper.

Short barrels and subsonics go hand in hand. Longer barrels serve only to increase a bullet’s velocity. Of course you have to register a rifle as an SBR with the ATF before you can install a barrel shorter than 16″, but this entire project is only interesting if you are already in the practice of registering NFA items like the suppressor you’re going to put on the end of the barrel.

The Subsonic Load

With the rifle in hand my goal was to work up a load that would shoot right at 1000fps — about .9Mach under comfortable atmospheric conditions, and safely below the transonic barrier where bullets start to make their own flight noise. But I also wanted one that would do so with enough energy to cycle a semi-automatic rifle action, and this has not been easily done in the past! It is compounded by the fact that no smokeless powders commercially available are designed for short-barrelled rifles. The military has specified and bought batches of powder customized for SBR loads, but they don’t leave any for sale to the public. For now reloaders are stuck with suboptimal options in terms of bulk and burning speed. The new standby for subsonic loads, TrailBoss, is too bulky to work in any rifle cartridge capable of firing and cycling both high-velocity and subsonic ammo. After significant research and testing I have found that the two best powders for subsonic SBRs are IMR 4227 and IMR SR-4759. In the case of the 7.62 Thumper XCR SBR, 12 grains of 4227 or 11 grains of SR-4759 over 220gr-240gr bullets will shoot right about 1000fps and, with a suppressor, provide enough pressure to reliably cycle the action.

These should not be confused with “less lethal” or riot-control projectiles. Rather, these are reusable primer-powered training bullets. I tested both .38 and .44 caliber versions.

Because they are powered only be a primer X-rings carry very little energy: They certainly will not cycle an auto-loading action. But they function seamlessly in revolvers when correctly loaded: In order to prevent the detonating primer from jamming itself against a revolver’s breech face it is necessary to drill out the primer pocket’s flash hole to 3/32″ on .38 brass and 1/8″ on .44 or .45 brass. (Note that with these expanded flash holes that brass should never again be used with standard loads, so it’s important to mark and segregate brass for use with X-rings.)

Loading X-ring ammunition is simple: seat a primer, then push a bullet into the neck of the case by hand. The average .38 X-ring bullet weighs 7.7gr, and the average .44 X-ring weights 14gr. I tested the .38s out of my 2″ S&W 642 revolver and the .44s out of my 3″ S&W 629. Longer barrels will only decrease muzzle velocity since primers produce so little propellant gas.

On the .38 I tested both WSP and CCI 550 “Magnum” primers and didn’t detect any significant difference in velocity. On the .44 I used WLP primers. I measured the average velocity for each load at 5, 15, and 21 feet:

Obviously these are not ballistically efficient projectiles. At these ranges they are as accurate as conventional ammunition, but even at 7 yards their point of impact has dropped almost a full foot due to their low velocity, which is decreasing so rapidly I don’t think they would be useful at much greater distances.

The great thing is that because they are so light the bullets will stop inside a cardboard box with a towel draped in the middle. They are reusable — the manufacturer claims that if they’re cleaned with silicone lubricant they are good for 75-100 firings. I didn’t see any degradation after shooting them five times. I noted that the first bullet through a clean barrel leaves a thin stripe of rubber against any sharp rifling, and that seems to buffer subsequent shots against wear.

It’s easy to clean a gun after shooting these: Any rubber peals away from the barrel with a single pass of a dry brush. However I was surprised at how dirty primers are: In the photo above you can see the fired nickel-plated case coated in a layer of soot, which also ends up in all the usual places on the gun. Immediately after testing I was able to wipe off all the fouling with a dry rag.

If you’re using conventional (lead styphnate) primers I would hesitate to shoot them in unventilated indoor spaces because this lead-laced fouling doesn’t all settle on the gun: It’s dispersed in the air, and it’s not good for you, especially if it accumulates in an enclosed space.

Finally a note of caution: These look like a tempting tool for close-quarters force-on-force training. Their impact energy is in the same league as a paintball, Simunition, or heavy air-soft pellet, which means that with adequate clothing and head protection these should in principle be safe to shoot at a real person. However, unlike those other projectiles X-rings fire from unmodified guns that are fully capable of shooting full-power ammunition. No matter how careful you are eventually a standard round will slip into a gun somebody thinks is loaded only with X-rings. Therefore, I would never fire these at a person, and I would always ensure my practice backstop can safely contain a real bullet.

This gun has a number of commendable features:

• It weighs just over 8 pounds, yet fires the medium-size .308 cartridge
• It has an 18″ barrel yet measures just 26″ overall (the shortest allowed for an unregistered rifle)
• It has a crisp 6.5-pound trigger, proving that bullpups don’t have to have terrible triggers
• It uses standard FAL magazines, which are widely and cheaply available
• It ejects spent cases forward, making it a truly ambidextrous bullpup

The RFB does have a few shortcomings that I will touch on in the course of this review, most critically in its gas system design.

The Biggest Challenge: Getting one

As of 2011 Q1 Kel-Tec has produced only 1500 of these rifles. The MSRP of $1880 hasn’t changed since it was first announced. Kel-Tec is irritatingly detached from the market for its products: The company increases neither production rates nor prices in response to ongoing high demand. Furthermore, the company only sells its firearms through an inscrutable network of distributors. To this day none of my dealers have been able to get their hands on an RFB. Meanwhile, people who do acquire them have always been able to scalp them on GunBroker.com for hundreds of extra dollars. Kel-Tec, obliviously, sells these to its distributors for under $1200.

I finally obtained one by learning through their fan forum that a batch was shipping to a particular distributor who was willing to make a direct sale to me (transferring, of course, through an FFL). My final cost was just $1350 which is considered closer to the “fair” street price than the MSRP.

The Bullpup Advantage

I have been a longtime fan of the bullpup firearm design, which places the action and magazine behind the trigger. The benefits are pretty clear in the following picture showing the RFB (18″ bbl) next to a comparable conventional semi-auto rifle (the FNAR, 20″ bbl) and a traditional bolt-action sniper rifle (the Savage 10FP, 26″ bbl).

The reduced length alone makes a bullpup much more practical for enclosed or close-quarters use. What you may not realize until you handle one is that the center of mass is moved so far to the rear that it is easy to shoulder and shoot, if necessary, with just one hand.

Kel-Tec also adopted one of the latest innovations in bullpups (first seen on the bulbous FN F2000): forward ejection. This solves one of the traditional drawbacks of a bullpup rifle, which is that it ejects right next to the shooter’s head. Side-ejectors are practically impossible to shoot cross-shoulder (to shoot weak side you have to hold the gun out from your shoulder to avoid eating hot brass). The RFB is truly ambidextrous. Kel-Tec earns extra points for a particularly compact action: The following photo shows it is slightly shorter overall than a Steyr AUG, even though the AUG only has a 16″ barrel!

Shooting

While relatively crisp, the RFB trigger is still 6.5 pounds. This may have limited my ability to wring the full accuracy out of the gun during my first test session, during which I fired three different cartridges, with and without a suppressor. Kel-Tec only claims this is a “2MOA” gun, and that was the best I was able to shoot with factory match-grade 168gr cartridges.

I chronographed 168gr BTHPM at 2510fps, 150gr BTFMJ at 2570fps, and 125gr SP at 2965fps. Kel-Tec lists an effective range of 600m for this 18″ barrel. Based on my chronographs this is indeed about the distance when these rounds will go trans-sonic.

Shortcomings

Kel-Tec chose to cut their 18″ barrel with 1:11.25″ twist rifling, which is on the slow end of standard .308 twist rates. This is not the best choice for the slower muzzle velocities produced by this short barrel, and it limits the ability of this gun to shoot the heavier and longer .30″ bullets on the market. 1:10″ would be a more logical twist rate. 1:8″, though not yet common in this caliber, would not only guarantee stability across the full range of .30″ bullets, but also would allow the gun to accurately shoot subsonic ammunition.

I found the pistol grip to be another shortcoming. It is made of a relatively slippery plastic and is not replaceable. Kel-Tec should have designed this rifle for compatibility with the vast market of modular AR-15-pattern grips, allowing owners to find a size and finish that suits their hands.

Design Flaw

The RFB gas system — the core of any self-loading rifle’s operation — has some serious design flaws. Kel-Tec seems to have developed theirs without any regard to the state of the art in piston-driven rifles. As a result their rifle is currently not suited to use with suppressors.

The RFB gas block is a simple T with fixed channel sizes allowing gas to flow through a forward exhaust port and backwards through the piston. The only means of controlling gas pressure on the action is to turn a “Gas Adjust” valve that changes the proportion of gas that can exhaust through the forward port, but that doesn’t restrict total flow through the gas block. This is the biggest design flaw in the gas system, and it makes this gun unsuitable for use with a suppressor: Suppressors boost total pressure on the gas system. Modern pistons offer a “Silencer” setting that compensates for elevated backpressure by severely choking flow through the gas block. Since the RFB can’t reduce the flow of gas from the barrel the manual instructs users to remove the “Gas Adjust” valve in order to maximize the ability of the extra pressure to vent out the forward port. This is exactly not what you want to do when shooting with a suppressor: The high-pressure gas venting out of the gas block is not contained by the silencer and so it creates its own loud report.

In theory Kel-Tec could correct this problem by replacing their “Gas Adjust” valve with a conventional “Gas Select” valve: A dial that extends across the barrel port in the gas block, completely obstructing the flow of gas. The circumference of a Gas Select valve is drilled with holes of varying diameter, typically offering four settings:

1. Off: No gas is allowed to impinge on the piston, making the firearm shoot like a single-shot “bolt” gun. This setting is great for testing accuracy and for minimizing noise when shooting suppressed.
2. Suppressed: The smallest hole allows the action to cycle under the extended backpressure created by a suppressor.
3. Normal: This is a hole large enough to cycle the action under regular conditions.
4. Boost: The largest hole provides extra gas pressure to cycle the action, compensating for underpowered ammunition or extremely dirty or cold conditions.

I.e., a proper “Gas Select” valve turns Kel-Tec’s “T” gas head into an “L” so that 100% of the gas tapped from the barrel impinges on the piston.

This takes us to the other gas design flaw: The RFB piston allows impinging gas to flow past its head when it cycles. The problem with this is that the piston vents into the carrier channel where the propellant gases then flow through the entire gun, coating everything in hot carbon. One of the key benefits of piston actions is supposed to be the isolation of propellant from the receiver. But in the RFB even the bolt at the extreme rear of the gun gets as dirty as the old direct-impingement AR-15 bolts I swore off years ago.

Kel-Tec needs to redesign the RFB piston to vent its gas outside and away from the receiver.

The AUG has a notoriously bad trigger. Not only is the trigger pull about 10 pounds, but it is also very “sticky.” Some people just shrug and say, “bullpups have bad triggers.” That’s not necessarily so. For example, Kel-Tec’s RFB has a crisp 6.5-pound trigger right out of the box. I will explain the origin of the AUG’s bad trigger as well as steps that can be taken to improve it.

The original AUG was an infantry rifle with a clever select-fire mechanism: Pull the trigger partly to the rear for a single shot. Squeeze it all the way to the rear and the gun fires a fully-automatic burst. For this feature to be reliable in the field the AUG was designed with a long and heavy trigger to avoid unintentional full-auto discharges. Perhaps compounding this design decision is the fact that militaries have not historically made “trigger feel” a high priority for infantry rifles; if anything a heavy trigger is considered a safety feature that reduces the possibility of unintentional discharges.

Steyr did not consider it worthwhile to create a smoother or lighter trigger for their semi-automatic-only trigger packs.

MSAR, which specifically built its rifle for the U.S. civilian market, doesn’t have a good excuse for copying the heavy AUG trigger spring.

One easy way to improve these triggers is to lighten the Trigger Spring (Part 13). Unfortunately this is a complicated piece — you can’t just snip a few coils from it — and nobody manufactures a replacement spring that’s any lighter.

Trigger Tamer

A few years ago Ben Langlotz realized that you can lighten the Trigger Spring by reducing the installed tension. He invented a clever device called the Trigger Tamer that replaces the standard Bolt Retaining Lock (Part 12) and engages the Trigger Spring at a higher angle. This part is covered by patent #7,165,352. The patent protection also explains how he can charge up to $60 for a cut piece of Delrin plastic. The following image shows a trigger pack with the Trigger Tamer installed on the left and a standard trigger pack on the right.

The function of the Trigger Spring is twofold: It presses against the Disconnect Lever (Part 10), providing almost all of the resistance to the trigger when the hammer isn’t cocked. In the standard trigger pack this sets the uncocked trigger weight at 5 pounds; with the Trigger Tamer that falls to 2 pounds. But the Trigger Spring also presses against the Bolt Retaining Lock, which keeps the Bolt Retaining Pin from sliding out and the back of the rifle from falling apart. The standard trigger pack applies 10 pounds of force against the Bolt Retaining Lock; the Trigger Tamer reduces this to no more than 5 pounds. The sample Trigger Tamer I received had a rough finish and was unable to return the Bolt Retaining Lock under so little spring force until I sanded both sides smooth with 400-grit paper.

After I installed the Trigger Tamer in my AUG the trigger pull was more than 3 pounds lighter, going from about 9 pounds to under 6. It was also substantially smoother.

Neu-Trigger

Matt Mikhail realized that a much of the “stickiness” in the trigger pull is the result of plastic-on-plastic friction, and further that the most significant source of friction is the pressure of the cocked hammer against the “sear” (i.e., the bridge of the Trigger Slide). Because the hammer is so light (being made of plastic) the Hammer Springs must be very heavy to ensure the hammer hits the firing pin with enough force to reliably ignite primers. Matt cut and bent a small tab of thin steel to wrap around the sear, producing a metal-on-plastic interface at this high-pressure sticking point. He sells this as the Neu-Trigger. He has applied for a patent and is currently charging $27 for the piece, shown installed on my MSAR trigger pack here:

I tested a Neu-Trigger and found that it not only smooths out the action considerably but also reduces the trigger weight by about 1.5 pounds. It’s not always a drop-in part: The corners of AUG sears sometimes need to be cleaned up for it to fit; MSAR hammer faces need to be sanded down in order to function with it installed. Nevertheless it’s a clever device that shows the shortcomings of plastic triggers!

Lubrication

Of course there is a lot of other plastic-on-plastic friction involved in the trigger action of the AUG. Note that it is important not to use any petroleum-based lubricants here since they could dissolve or weaken the plastic. I tried lubricating the numerous contact points of the Trigger Slide with molybdenum disulfide but was unable to measure any significant effect on the trigger pull. Ben Langlotz sends three pages of instructions with his Trigger Tamer for disassembling, polishing, and lubricating the trigger pack and trigger bars. While these only reduce the trigger weight by a few ounces he claims they substantially smooth out the trigger action.

At this point I am hoping for someone to bring to market:

1. A Trigger Spring 3 pounds lighter than the current standard.
2. A metallic “match-grade” trigger pack where all critical interfaces can be held to higher tolerances, polished, and lubricated to produce a trigger pull as light and smooth as we can get on any other quality rifle.

[2012 Update: For the best trigger improvement see the new RAT WORX Hybrid Trigger Mod.]

Ever since its adoption field reports have complained about its marginal stopping power. In recent years our military has spent a lot more time in wide battlefields with optics good enough to reach out to and beyond the nominal 400-yard “effective range” of the 5.56mm. It may weigh twice as much, but nobody questions the ability of 7.62 NATO to stop human targets out to 800 yards. (Beyond that is the realm of trained snipers, who may step up to .300 Win Mag or .338 Lapua Mag cartridges with effective ranges beyond a mile.) There has also been a lot of recent work on other cartridges that fit within the 5.56x45mm profile but provide better ballistics and stopping power, 6.8SPC being the most widely adopted of that family.

This is a photo of the Kel-Tec KSG: A brilliant bullpup pump-action shotgun with dual selectable magazines and capacity for 14 rounds. It was just announced in January 2011. Because it’s a bullpup it will be easier to handle than any conventional shotgun. The parallel magazine tubes make a “switch-to-slug” operation as easy as flicking the magazine selector. Everybody who wants a pump-action 12-gauge and can afford it will buy at least one of these.

I hope a company with more manufacturing capacity copies this design. Kel-Tec produces several ingenious guns but they have never been able to meet demand. I know dealers who have been on waiting lists for guns like the Sub2000 and RFB for years. Demand for the KSG will certainly be orders of magnitude greater than anything they have yet produced. Freedom Group, please steal this design!

[March Update: Never mind! UTAS has announced they will begin domestic production this year of the UTS-15, a bullpup shotgun very similar to the KSG. Advantages over the KSG apparently include locating the magazine tubes above the barrel (for better recoil control), round-count indicators, and the ability to automatically alternate tubes with each shot (to keep it balanced). A disadvantage appears to be that it ejects sideways. The South African NEOSTEAD is another similar bullpup pump-action shotgun, and the only thing keeping it out of the U.S. is the silly BATFE restriction on importing shotguns that are not sufficiently suited to "sporting purposes."]