AR-15 “Pistol” PDW

AR-15 .300BLK Pistol PDW

This is my recent AR-15 pistol build. The upper assembly from CMMG was $700 and features a KeyMod free-float handguard and 8″ medium barrel. It is chambered in .300BLK, which is currently the most versatile and efficient AR-15 caliber for such short barrels. I assembled the lower from a Seekins Precision forged receiver, Phase 5 Tactical pistol buffer tube, Noveske QD end plate, CMC 3.5lb single-stage trigger, and Stark SE-2 grip. Total component cost for the lower was $450. Unloaded weight for the complete firearm is only five pounds.

A generation ago sub-machine guns were the middle ground between handguns and full-power rifles. A famous photo from moments after the 1981 assassination attempt on President Reagan shows a Secret Service agent readying an Uzi he had produced from a nearby briefcase. We have since learned that power is more important than volume of fire, and that guns on full-auto with concealable magazines run empty far too quickly. Today the niche between handguns and long guns is filled with rifle-caliber “personal defense weapons” (PDWs), which are powerful enough for a serious gun fight but still portable enough for every day use and potential concealment.

AR-15 Pistol and Short-Barreled Rifle (SBR) lowersThe advantage of a “pistol” AR-15 is that it can be equipped with a barrel shorter than 16″ without the hassles of registering it as a Short-Barreled Rifle (SBR). What qualifies it as a pistol is that it doesn’t have a full stock or second vertical grip, yet the buffer tube required for the AR-15 to function can serve in a pinch as a three- or four-point mount, providing accuracy on par with a traditional carbine. (The ATF, struggling to make 80-year-old laws look reasonable in spite of evolutions in gun design and tactics, recently ruled that even arm braces do not turn a pistol into an SBR.)
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NFA Rules on Pistols, PDWs, AOWs, and SBRs

The National Firearms Act (NFA) was enacted in 1934 in an attempt to control weapons popular in Prohibition era gang warfare. After eighty years its implementation by the Bureau of Alcohol, Tobacco, and Firearms (ATF) has become rather strange, and its controls on items like short barrels and suppressors seem archaic.

The following infographic shows a variant of the XCR with a 10″ barrel. This is a piston-operated autoloading firearm that can chamber a variety of light rifle cartridges. Under federal law the top three configurations are considered pistols, and no special controls apply to their construction, sale, or possession. (State laws can vary widely on these matters, so those are not addressed here.)

Something weird happens in the fourth configuration: Adding a second vertical grip turns it into an NFA-regulated firearm called an “Any Other Weapon” (AOW), and would be a felony if the receiver were not already registered as an AOW.

To comply with the NFA I had to use a different receiver registered as a Short-Barreled Rifle (SBR) for the last picture.

Infographic: NFA Rules on Pistols, AOW, and SBR

Hollywood Reality Check: Stun Guns and Tasers

Not long ago the knockout myth was a staple of action shows: Heroes could drop victims cold with a single karate-chop to the back of the head, then carry on with no concern they would regain consciousness before the end of the scene. Fortunately, increasing awareness of the seriousness of brain injury has relegated this plot device to farces. In reality any blow that knocks somebody out for longer than a few minutes is likely to cause extended and often permanent brain damage.

But Hollywood has replaced the knockout blow with an even more absurd gag: the stun gun, which with a single zap appears to drop victims to the ground and render them unconscious long enough to be moved and tied up. The reality is that electroshock weapons are far less reliable and effective, but also very interesting.

Typical Stun GunBasic electroshock weapons are often misleadingly called stun guns. They create a high voltage charge between two electrodes. When pressed against a conductor like human skin low current flows through the conductor between the electrodes. The current triggers pain receptors, so the victim feels extreme pain, but the sensation is localized to the area between the electrodes. The shock may be startling, but its effects are limited to the individual’s reaction to pain. A typical person will recoil from the shock and try to avoid continued contact. An angry person might just get more angry.

In order to cause more dramatic reactions electric current needs to travel through muscle. Taser International pioneered the development and publicity of electroshock weapons that can cause major muscle groups to involuntarily seize up, usually resulting in victims falling to the ground, incapacitated. There is some fascinating science behind the exact methods Taser uses to achieve these results without endangering a victim’s heart, worth reading in this feature by the IEEE.Taser X26

But Tasers are not magic wands: A lot has to go right for them to work effectively.

First, the electroshock effect only lasts as long as the current runs: As soon as the current stops or the circuit is broken the victim suffers no lingering impairment. To maintain contact Taser electrodes are actually hypodermic barbs. (This fact surprised me, especially since the barbs often punch through clothing and draw blood. A Taser engineer I talked to noted that more than a million people have been voluntarily “tased” and there have been no reports of associated infections. He mused that the electric current may have a sterilizing effect, though there has been no scientific study on that question.)

Electrodes have to span core muscle groups to cause incapacitation. If the barbs are too close to each other their current path, and hence their effects, will be localized. The electroshock effect also depends on where the electrodes hit: Areas with few muscles and nerves, like the lower rib cage, do not reliably incapacitate. However Taser electrodes are also barbed on their sides so that a victim attempting to pull them out to stop the pain will likely complete a highly incapacitating circuit leading from his hand through his chest to the other electrode.

Because the electrodes need some separation Tasers are ideally discharged from a short distance. Two electrodes are propelled from the weapons with an 8 degree vertical spread. In less ideal conditions one electrode can miss, in which case the victim gets no shock. Or the victim could be too close for the electrodes to spread adequately. In those circumstances Taser trains users to “drive” the weapon into contact with the victim: in addition to the fired electrodes a Taser cartridge contains contact electrodes, and its circuitry can detect which one to energize to complete the largest circuit on the victim.

It is possible to “armor” against Tasers by wearing conductive clothing or spray-on coatings. However if you’re armoring yourself against Tasers you should consider that the next steps in the escalation of force are impact weapons or firearms, which will more likely cause serious injury or death. (This is why Tasers are so popular with law enforcement: In many scenarios they can cut short altercations that would otherwise require officers to tackle or grapple subjects, resulting in frequent injuries to both parties. Although that benefit has been tarnished by disturbingly many incidents in which officers abuse Tasers to inflict pain or assert power in non-violent confrontations.)

So, clearly Hollywood is getting it wrong when they depict simple stun guns incapacitating people, or advanced electroshock weapons like Tasers knocking people out. Please stop.

Curious Prices in the PC RAM Markets

A year ago I bought 8GB of DDR3 RAM for $45. I just bought another pair of DIMMs with identical specs and paid $77. Prices spiked to this level during 2013 Q1 and have not retreated, in what seems a blatant market violation of Moore’s Law. Some commentary on this situation notes that historically DRAM producers have whipsawed between cutthroat competition and nearly (if not explicitly) collusive pricing power.

The Problem With Nickel-Boron

A few months ago I discussed metals and coatings for firearm actions. I noted the NiB (nickel-boron) gets discolored by fouling, but my photos only showed a sparkling new NiB-X BCG. Following is a picture of what it looks like after a few hundred rounds of use, followed by ultrasonic cleaning and then aggressive scrubbing with steel and brass wire brushes. For comparison I show my heavily-used chromed BCG on top.

AR-15 bolts: Chrome and NiB-X, as clean as they get

Is this just a cosmetic issue? This is the only cleaning I’ve given the NiB BCG. I haven’t lubed it and I have subsequently run a few hundred rounds more without any action failures. However it seems plausible that if fouling can bind to the surface this stubbornly it could build up to the point of overtaking the nickel-boron’s lubricity and causing a stoppage that only traditional lubricants prevent. As noted in the original article this is not a problem with chrome and NP3: All photos of those to date have been after they were used and wiped clean with minimal brushing.

Reloading Adventures: Rounds Stuck in Chambers

I reload for half a dozen guns in .308 Winchester. Reloading is a lot easier if you only have to neck-size fired cases. Until recently I kept all brass segregated by rifle, and only “full-length” case-sized brass that came out of semi-autos (which are under enough pressure during extraction to bulge the case body). Then I thought I’d get clever and see if any chambers were cross-compatible, allowing me to use brass fired in one gun in others without full resizing. Sure enough, a handful of fired cases suggested that all my bolt-guns were interchangeable.

However, since this apparent epiphany I have broken a CTR stock, a Savage bolt handle, and five cleaning rods in the process of extracting rounds stuck in chambers. I have also resolved to small-base-size any case that isn’t being reloaded for the bolt gun in which it was last fired. Here are some nuances I’ve learned.

Evidently fired case size isn’t consistent. Even though I’ve been using a single lot of brass, not all loads fully form the case to the chamber. Presumably even if I stuck with the same load the brass would exhibit different springback on subsequent reloadings as it work hardens.

I eventually discovered that my DTA chamber has a relatively large base, which led to my other painful discovery: “full-length” rifle sizing dies do not necessarily size the whole case. For example, when properly set, my Lee full-length .308 die doesn’t even cover the bottom quarter inch of a case. Only a “small-base” sizing die will ensure the entire case is squeezed back into spec.

My other irritating discovery is that few “case gauges” check for full chamber fit. The Wilson case gauges I had been using all along are actually overbored to ensure they can measure fire-formed brass. They are only meant to check headspace and trim length. The fact that a case clears a Wilson gauge is insufficient to determine whether it will chamber in any gun. The only gauge I could find to guarantee chamber fit is the blue JP Enterprises one in the middle of this picture:

L.E. Wilson gauge, JP Enterprises gauge, formerly stuck round

The JP gauge is cut to the minimum SAAMI chamber spec, which means that if a round clears it and fails to chamber you’ve got a chamber problem, not a case size problem. But we’re talking about very fine tolerances. The round in the JP gauge in the picture is actually oversize enough to jam in my Savage. You can barely tell that by looking, but you can feel the base protruding ever-so-slightly at the rear of the gauge.
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Hand-discharging loaded rounds

Hand-fired loaded round

This sequence shows me discharging a loaded round I couldn’t disassemble. There is no reason to ever do something like this other than brazen curiosity. If you want to disable a live round you should pull the bullet and dump the powder. If for some reason that fails a safer alternative to discharging it is to “cook it off” in an open pit fire. (Ensure that anyone not wearing a face shield and thick clothing stands clear until it pops.)

Firearm cartridges are not particularly powerful or dangerous unless they are tightly confined. Without a gun barrel to contain and direct the pressure smokeless powder burns slowly, if at all, and bullets are propelled only by the force of the primer. (Granted, primers are not toys. They are true explosives. Small firearm primers produce 5-10 foot-pounds of energy, and can produce pressures on the order of 25kpsi in a small closed chamber. Like firecrackers, they can burn and maim.)

The round I had on my hands contained a full load of powder that turned out to be too fast for the bullet. I managed to pull the rest of the batch, but one bullet came out and left its copper gas check in the case. In that condition it could have been safely fired in a gun, except that it could have badly fouled the bore depending on how the gas check engaged it. So instead I drilled a hole in a piece of wood to tightly hold the case neck, put on leather and a face shield, then detonated the primer with a steel punch.

Integral .300BLK case and bullet on the left; hand-fired case and bullet missing gas check on right

An integral pulled bullet and case are shown left. The hand-fired case and bullet missing its gas check are on the right.

The problem with any containment when discharging a round is that without experience and knowledge of the case and powder you may be surprised at where the force ends up. The unsupported case could become a projectile or fail and produce shrapnel. The bullet and any other particles in the path of the venting gases can also be ejected almost anywhere. The setup above was carefully planned to allow for the worst possible outcome in every dimension. What actually happened is that the case neck held fast in its hole in the upper plank and the unsupported annealed upper body was blown out by the pressure, but did not fail. The gas check ended up embedded in the bottom plank directly below, and the gas was able to vent out the gap between the planks, blowing only minor wooden debris along with it.

Products I’m looking for in 2014

Arms

  • Supply in the firearms industry is finally starting to converge on demand. But reloaders are still grasping for powder, and .22LR is still absurdly scarce. We’re looking for both of those shortages to end by the middle of this year.
  • Expanding subsonic rifle bullets: Looks like this is finally the year for these to hit the mainstream market. Outlaw State Bullets and Lehigh Bullets have had some expensive offerings. But this year Norma is supposed to begin importing their Plastic Points, and Remington should finally have an offering tailored for their 300BLK.
  • .38 Supercomp Sig and Glock conversions. The caliber offers the ballistics of .357 Sig in the diameter of 9mm, which translates to more magazine capacity. Also, as a straight-walled cartridge it’s easier to reload.
  • Laser Doppler Anemometers: Solid-state devices for shooters, similar to laser rangefinders, that can measure downrange winds. Winds are the last primary ballistic factor that can’t be measured outside instrumented ranges. Even the most skilled long-range marksmen in the field have limited indicators from which to read and compensate for windage. Admittedly this technology is still some years off from commercialization.
  • Chemical laser guns. Well maybe not this year, but the technology is there for it.

Cars

Video

  • High-speed consumer video cameras: GoPro may be inching back into this niche left by Casio four years ago. Their top offerings can now sustain 240fps at 480p, but I’m still looking for thousands of frames per second in a sub-$1000 camera, which is no stretch given the state of the art.
  • Reasonably-priced HD IP security cameras: For some reason these persist at over $200 when the state of the art should have them closer to $100.
  • Digital thermal and night-vision gear: No manufacturer seems to want to lunge for the tipping point. Equipment that is currently produced at a small scale, and therefore costs 4- or 5-figures, could be profitably mass-produced and sold for 3-figures to the sport and non-military security markets.

Barrett MRAD

Barrett MRAD

The Barrett MRAD is a $5800 precision multi-caliber bolt-action rifle, shown here with a 24″ barrel in .338 Lapua Magnum, and a $500 quick-detach LRA bipod. The MRAD sets new standards in modularity, simplicity, and compatibility by combining a number of clever design features:

  • Like most modular rifles its folding buttstock locks into place over the bolt handle. It adjusts for length-of-pull with a button, cheek height with a thumbscrew, and features a bottom rail for mounting a monopod.
  • The upper is a beautifully milled if oddly anodized piece of aluminum with 30MOA of cant in the top rail.
  • It uses robust and reasonably priced double-stack injection-molded 10-round magazines. (However they can only hold rounds up to 3.8″ long, which may limit the reloading envelope of heavy VLD bullets.)
  • Upper and lower receivers separate with one lever and one captive drift pin.
  • It accepts standard AR-style grips. It is shown here with a Magpul MOE.
  • It uses a traditional AR-style short-throw safety.
  • The bolt has an automatic self-lubricating dust cover.
  • Its barrel can be rapidly changed out the front after removing two bolts, and reinstalled without losing zero.

Barrett MRAD field strip

Barrett MRAD trigger groupAfter pivoting the gun open the bolt comes straight out. The safety can be pushed out without tools at which point the trigger module can be lifted out. The trigger itself deserves special attention: It is as simple as can be and elegantly executed. Adjustable down to 1.5 pounds, it breaks shots consistently with no creep or overtravel — an ideal specimen for precision shooting.

And this rifle is precise! Following is the very first group shot at 300 yards after zeroing at 200 yards. Using my preferred handload with Lapua brass and 250gr Lapua Scenars this 5-shot group is right about 0.6MOA.

Quarter-MOA 5-shot group at 300 yards

As shown the rifle weighs over 17 pounds, so it makes shooting the heavy .338LM quite tolerable. After several years of delays Barrett is just now bringing caliber conversion kits to market for $1500, allowing owners to switch bolt, barrel, and mags to shoot lighter, cheaper .308 or .300WM from the same gun.

The only shortcoming as delivered is that the bolt knob is a cheap piece of injection-molded plastic. Presumably it is meant, like that standard grip, to be replaced by the end user with his preferred bolt handle.

Precision Sniper Rifle (PSR)

In 2008 the US Special Operations Command (SOCOM) began soliciting a new “Precision Sniper Rifle” (PSR) to fill the gap between the .308 M24 and .300WM M2010 (both manufactured by Remington) and the M82/M107 .50BMG rifles (by Barrett). The primary cartridge for the PSR is the .338 Lapua Magnum.

A unique objective of the PSR program was to procure a system that would allow for rapid barrel changes in the field, including conversion to fire the smaller .300WM and .308 calibers using the same chassis and optic. The precision specification was already quite demanding — a consistent vertical spread of no more than 1MOA over a statistically significant number of trials. Constructing a system in which a barrel could be removed from the action in the field and then returned to the same zero may have previously be unthinkable.

It turns out plenty of civilian shooters were just as interested in owning a multi-caliber precision rifle. Shown here are three that were designed for the PSR program and made available for sale to the civilian market.

Barrett MRAD, AI PSR, DTA SRS

On top is the Barrett MRAD. Initially offered only in .338LM for $6000, Barrett just brought its $1500 conversion kits (bolts, barrels, and magazines) to the market.

In the middle is Accuracy International’s PSR, currently sold only as a complete kit with all three calibers for $17000.

Bottom is the bullpup Desert Tactical Arms SRS, the bargain of the group at $3000 for the chassis and roughly $1500 per caliber kit. We previously reviewed the DTA SRS. Of the multi-caliber PSRs it currently seems to have the greatest market penetration. It is also available in the widest array of calibers, and even has third parties manufacturing conversion barrels.

The PSR contract was finally awarded this March to Remington’s “Modular Sniper Rifle,” which will probably not be available for civilian purchase until government demand has been satisfied.