Category Archives: Arms

Shooting Bullets Into Water – Part III: Underwater Ballistics

In Part I we noted that water provides a good model of a bullet’s terminal ballistics. We discovered that while slow rifle bullets don’t deform in water they do destabilize and virtually stop after a few feet. At higher speeds they mushroom and/or disintegrate, again causing them to stop within a few feet.

In Part II we discovered that conventional bullets will ricochet back out of the water when fired at shallow angles, but that bullets fired base first are uncannily stable. There has been long-standing military interest in producing bullets that can be fired into or under water and retain accuracy and energy over any significant distance. Supposedly very long tungsten-core bullets (with extreme sectional densities) can “swim” up to 40 feet, but those are experimental projectiles that require special guns.

Curious to see what sort of distance and accuracy could be obtained by the common rifleman we did a series of studies with 225gr Hornady OTM .30″ bullets. First we checked the effect of velocity. Fired base-first these bullets begin to deform about 2000fps on impact with the water. They disintegrate above 2200fps.

About half the time there is a second significant cavity that forms 4-8 feet from water entry, and most of the time when it does form the bullet diverts as much as 45 degrees from its original trajectory. An example is in the following still:

The most consistent effect of the higher velocity bullets was to increase the size and redirection of the second cavity. Bullets fired at 1000fps traveled about 14 feet, while the 2000fps bullets “swam” about 20 feet before essentially stopping and sinking to the bottom. The distinction is that the slower bullets pretty much followed a straight line and didn’t suffer significant deflection or secondary cavitation.

The bullets give up about half their speed within the first 5 feet of water, but are they good enough for fishing? We set up an underwater target 7 feet from the point of entry into the water and fired at an angle of 7 degrees to the water’s surface from a distance of 25 feet. A string of 5 subsonic shots printed a group on the target with an extreme spread of 7″. I’m not a fisher, but in comparison to traditional rifle bullets, which aren’t effective beyond 3 feet, these base-first bullets are remarkably effective in terms of both underwater precision and swim distance.

Shooting Bullets Into Water – Part II: Ricochet

In Part I we noted that water provides a good model of a bullet’s terminal ballistics. We have also spent some time with our water facility and the high-speed imaging technicians from Aimed Research studying the dynamics of ricochet.

Following extensive experiments we have observed that pointed and round-nosed bullets will almost certainly ricochet out of the water when fired at incident angles flatter than 10 degrees. Even superstabilized bullets leave contact with the water tumbling erratically, and give up as much as 90% of their energy to the impact.

Aimed Research provides high-speed video of the behavior. This is a 225gr .30 caliber bullet:

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Shooting Bullets Into Water – Part I

What does a bullet do when it hits something? We have done extensive ballistic testing on water and will detail our results over the next few posts.

Why water? For one thing it’s a good simulant of soft animal tissue. Real animals may be the targets of any study, but given their bone and organ distribution it can be hard to get consistent results. For scientific purposes the standard medium for studying terminal ballistics has been calibrated gelatin, usually 10-20%. This allows for careful analysis of penetration and wound channels, but it is also a pain to prepare. If you are just interested in what happens to the bullet it turns out that a large tank of water has the same effect on projectiles and allows for easy recovery.

It was during water testing that we were first struck by the behavior of standard rifle bullets at subsonic velocities: They don’t deform at all. You can almost just polish out the rifling marks and load them again:

It takes high-speed video to see that even though they don’t expand these long rounds destabilize almost immediately on entering a body (of water, or otherwise). The following videos were provided by Aimed Research (which maintains a fascinating YouTube channel):

Two other videos are here and here.

For reference: At supersonic impact velocities hunting bullets expand. Following are four examples. The left-most is a solid copper alloy. The others are lead-core bullets with various expanding and bonding mechanisms designed to retain enough mass in the copper jacket to penetrate while dissipating some lead in the target shortly after impact.

“Bullet gel tests” are easy to find online if you want to see exactly how and when a particular bullet expands. Here is a striking microsecond image from one of Aimed Research’s gel tests:

Stuck Case Removal Trick

If you full-length size cases during reloading this will eventually happen to you: You’ll run a case into the sizing die and then rip the rim off trying to extract it. At this point you’ve stuck the case in the die and normally you have a long ordeal ahead of you to get it out so you can keep reloading. Some poeple don’t even bother trying and instead send the die back to the manufacturer to get the stuck case removed.

I’ve never been able to free a stuck case with penetrating lubricants: Evidently the brass forms a very tight seal with the die. You can buy or improvise a “stuck case remover” system consisting of a drill, tap, screw, and standoff washer. With a lot of work you can tap the case head and use a fine-threaded screw to slowly pull it out. I’ve done that.

Then I came up with the following trick:

Stuck case removal trick

It takes advantage of brass’s high thermal conductivity and the fact that metals shrink when cooled. By spritzing the exposed brass with super-evaporative coolant — the trifluoroethane that sprays out of an inverted dust-off can is convenient — the brass will quickly shrink and separate from the die. You then have a moment to either hammer or screw it out with the die’s decapping rod.

Note that you can only hammer it out if the die allows you to unscrew the rod from the die body. In this case don’t take the locking bolts all the way off the rod though, since hammering may mushroom the top of the rod enough that you’d have to grind it to get the locking bolts back on. If you’re going to screw the rod in to push the case out then take the locking bolt off and before spraying the case have the rod screwed into the web of the case head so it’s ready to push.

Savage .308 Precision

Savage 10FP in .308 Winchester with Sightron SIII 8-32x56 scope

I had so much fun testing my 10/22s for precision that I decided to run analysis on my .308 Savage 10FP. This has been my benchmark medium rifle for almost a decade now, and has been abused accordingly: I have broken the bolt handle at least once and had to hammer out and even drill out stuck cases. How accurate is it now?

I shot the following two groups of Hornady 168gr OTM handloads at 100 yards. I only had 8 rounds of the first load, which uses Federal GMM cases with 44.4gr Varget. The second group is 10 shots from LC 04 cases with 44.7gr Varget. (This batch of Lake City brass has .2gr more water capacity than the Federal. The LC loads chronograph about 2850fps vs 2840fps for the FC loads. Keep in mind this is a 26″ barrel.) All loads are seated to 2.80″ and use FGM210M primers.

8-shot group 10-shot group

Based on these 18 data points the rifle with these loads has CEP = 0.30″ at 100 yards, or .28MOA. (The 90% confidence interval is .25″-.32″.) This means its 4MR is 1.3MOA — i.e., 96% of shots fired should stay within a 1.3MOA cone.

10/22 Precision Rifles

KIDD 10/22 in Archangel stock, Ruger 10/22 with Feddersen barrel in Vantage stock

These are both Ruger 10/22 style rifles built for shooting .22LR with maximum accuracy. On top is an $860 rifle built entirely by KIDD Innovative Design. The receiver and trigger are milled from aluminum, and the bolt from hardened steel. The single-stage trigger is also a crisply machined assembly that adjusts down to a pull of just 1.5 pounds. The lightweight barrel is guaranteed to group inside of half an inch at 50 yards. The gun here is screwed into a comfortable $100 ProMag Archangel Target stock

Do you have to spend $1000 to get an accurate .22 rifle? Expert barrel maker Fred Feddersen says one of his $170 barrels will turn an off-the-rack Ruger into a gun that can compete with any custom autoloader. So the second gun shown is a standard Ruger 10/22 receiver and bolt onto which I swapped Feddersen’s barrel. Of course I don’t think I can really shoot that well with a standard trigger, so to be fair I bought another $200 KIDD trigger assembly for it. The gun is shown here screwed into a beautiful $175 Tactical Solutions Vantage laminated stock.


The ammo shortage continues to plague the market for .22LR, so I consider myself lucky to still have four different types of ammo on hand. I screwed an AAC Element suppressor to each barrel, put each rifle in the Archangel stock, mounted the same high-power scope, and shot ten-round groups at 50 yards with the following subsonic 40gr loads:

  • Eley Match
  • SK+
  • CCI HP
  • Aguila SuperExtra

I have plenty of the Aguila on hand, so I used that for sighting and shot two groups with that. The Ruger/Feddersen fired all 50+ shots without any hiccups. The KIDD began to bog down at the end, experiencing a few failures to fire or extract on the Aguila. Cleaning the chamber and bolt face and testing some more showed it’s capable of running smoothly when clean, but evidently it doesn’t like too much of the copious .22LR fouling to build up. Do those tighter tolerances translate to higher precision?
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Rimfire Suppressors: Lessons and Warnings

One of my first suppressors, registered ten years ago, was a GEMTECH Outback-II: a lightweight can designed for the diminutive pressure and volume generated by .22LR cartridges. As was common at the time the suppressor was not designed to be routinely opened and cleaned.

This is a big mistake for a .22LR suppressor, and here’s why: .22 rimfires are very dirty. Over time layers of condensed lead, hardened with powder byproducts and bullet lubricant, will accumulate on the baffles that are supposed to disperse the propellant gasses inside the can. After thousands of rounds the silencer can double or triple in weight and lose most of its sound attenuation as it clogs with lead.

A few years ago one licensed manufacturer, SRI, began to “jailbreak” old suppressors that weren’t originally designed to be cleaned: for a few hundred dollars they clean or replace the old core and fit an endcap that can be easily unscrewed. Curious as to just how bad the problem can be I decided to open my Outback II. (Doing this in a non-destructive fashion took quite a bit of work, a lot of penetrating lubricant, and a few special tools.) Here is what the baffles looked like:

Outback-II aluminum baffles after thousands of rounds

For comparison, my latest rimfire suppressor is an AAC Element II, designed to be routinely opened and cleaned, and here is what its baffle stack looks like when new:

Baffle stack from AAC Element II suppressor

Partially sandblasted aluminum baffles from old Outback-II suppressorJust how bad is that fouling? I spent about two hours with a sandblaster trying to clean the Outback’s aluminum baffles. Here’s a picture with two done and two just begun:

I can see why many consider it better to just replace the baffles once they’re this bad. The fouling on the inside cone of the first baffle was so stubborn I simply could not get it off with a sandblaster. Some people report better results wet tumbling baffles with steel pins for a day or two. However any mechanical cleaning strong enough to remove the lead alloy that builds up will eventually degrade the facets of the baffles themselves — especially those made of aluminum.

Is this avoidable? One experienced gunsmith I know has always applied lithium grease every few hundred rounds to his rimfire silencers. After thousands of rounds his suppressors have no buildup that can’t be wiped off with a cloth. Anti-seize and other heavy lubricants are also used for this purpose.

Lessons learned:

  1. Don’t buy a rimfire suppressor you can’t open to lubricate and clean.
  2. If you have a sealed suppressor you shoot a lot of unjacketed bullets through then eventually you’ll need to get it opened and cleaned.

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