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.

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.

Basic 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.

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.

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:

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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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.

After 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.

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.

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.

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.