A precision-obsessed friend was lamenting the apparent inability of his Robinson XCR to shoot tight groups. Although it was not designed specifically for precision, I am a fan of the gun’s design. Particularly given its ease of changing barrels, I began to wonder how much we could improve on the standard chrome-lined light-contour barrels. So I sent two Lothar-Walther match-grade 1:8 rifled stainless steel blanks to Robinson and waited (seven months) for them to return as heavy-contour 11″ 5.56mm XCR barrels.
This is not a gun that is easy to shoot precisely: It is light, and its single-stage trigger breaks at over 4 pounds, which I know robs me of accuracy. In order to remove shooter dispersion from the equation I tested various configurations in a custom machine rest. I ran a range of ammunition through two standard 11″ barrels and, sure enough, 10-round groups would typically exhibit a mean radius in the vicinity of 1.5MOA. The standard 16″ light barrel, interestingly, printed 10-round groups with MR just above 1.0MOA shooting light bullets (both XM-193 and Wolf Classic!), but didn’t do as well with heavier bullets in match-grade loads (despite its 1:9 twist).
With the new precision barrels the rifle prints 10-round groups with mean radius consistently below 1.0MOA, like these:
Note that from the short barrel 75gr .223 loads run about 2260fps. On the high end, 55gr 5.56mm clocked 2775fps.
There is some vertical stringing evident, which varies with the upper, and which suggests there is further room to tighten the design. And, as mentioned above, these groups were achieved with a machine rest. When I shoot off of bags 10-round groups open up by roughly another 0.5MOA. Suffice it to say that with a good barrel and shooter this gun is capable of respectable accuracy.
Here’s my annual gift to entrepreneurs: If you want to make money, bring any one of these items to market and I guarantee you success!
More heavy subsonic .22LR ammunition. The market above 40gr is still limited to the Aguila 60gr load!
Gapless revolvers. The Nagant 1895 Revolver goes into battery when cocked to seal the cylinder gap. Revolver manufacturers pride themselves on their lockwork but the biggest innovation in revolvers in the 120 years since the Nagant went into service has probably been the shift of the barrel to the bottom of the cylinder with the Chiappa Rhino line. How about a revolver that is normally in battery and only cams out of battery to open or rotate the cylinder? Eliminating that loud, dangerous gap would be very cool, and doing it with a nice trigger pull would be a worthy achievement for a revolver engineer.
3-mode single/autoloaders. Historically automatic rifles have had a three-mode selector that toggles between Safe, Semi-automatic (one shot per trigger pull), and Automatic (typically either a 3-round burst or continuous fire while the trigger is depressed). For the civilian market that third mode has been eliminated. But there is another mode that would not be restricted that I would appreciate having in its place: Call it Manual, which would fire a loaded round but not cycle the action. The biggest benefit would be found shooting suppressed, where the option of keeping the action locked up would result in quieter shots and less fouling. The Manual mode would also be a useful tool for training. Granted, it is possible to run some piston guns in manual mode: the Ruger SR-556 and the XCR have gas selectors that can close the gas system completely. But they aren’t designed to be easily toggled the way fire control switches are.
Faster, cheaper, higher-resolution video cameras. As of now there is a gap between the $5500 Edgertronic, which can shoot 720p at 700fps and lower resolutions up to 18kfps, and (of all things) the $900 iPhone 6 which maxes out at 240fps in 720p. No camera in the consumer price range offers sustained video above 240fps!
We’ve been questioning what sort of precision we can expect from a piston-driven rifle with a chrome-lined bore. Those are both features believed to reduce accuracy (vs direct-impingement and an unchromed bore). We tested our Ruger SR-556 shooting ten-round groups using the same suite of ammo as in our Savage .223 Precision test and got CEP across the board about 1 MOA (with the exception of the bottom-of-the-barrel Wolf Classic, which produced CEP of 1.5 MOA).
This weekend we got a chance to try a little harder with a Barrett REC7, a premium rifle. Shown above, we fitted it for this test with an LRA bipod and NightForce F1 scope. Five shooters took 10 shots each with two different types of ammo. Given the conditions the shooter variation was minimal. The ammo makes the difference, and this gun sets a new precision benchmark for its type:
|Federal Gold Medal Match 77gr
|American Eagle XM193
A traditional tracer bullet like the M62 carries an incendiary payload in its base. We’ve done a lot of experimenting with bullets fired “backwards” (i.e., base first), and found them to be both accurate and effective, even if their blunt shape produces excessive long-range drag.
So what happens when you fire a tracer base first? First of all, the tracer doesn’t ignite in flight. But if it hits something hard, like a rock or steel target, the jacket ruptures and the impact energy usually ignites the tracer compound all at once, producing a satisfying flash and puff of smoke, leading us to call them “flash rounds” or “smoke rounds.”
Once again our friends at Aimed Research provided a high-speed video of a flash round hitting a metal target:
Granted, these are nothing like a “true” incendiary round, which sounds like a cherry bomb exploding. Following is a video of a real incendiary bullet hitting the same metal target. It has a larger payload of fuel (magnesium and/or aluminum) and oxidizer (barium nitrate).
Continuing precision testing my guns I took my old Savage 10FP to the range with boxes of six different commercially-available .223 Remington rounds. The rifle has a 24-inch 1:9 heavy barrel installed in a Choate Ultimate Varmint Stock, which makes it a superb bench gun. I mounted the 14x Nikon scope before I had found good Quick-Detach mounts, and before I had concluded 20x is my preferred minimum for precision shooting. But it’s still fine for setting a baseline with commercial ammo:
|Black Hills 75gr Match
|Georgia Arms 69gr Match
|Wolf Gold 75gr Match
|American Eagle 55gr
|Silver Bear 62gr
|Wolf Classic 55gr
The 100-yard target can be reviewed here.
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.
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:
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:
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:
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.
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.
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.