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You’ve read a lot of tests, but this one will not have any charts of velocities, charts of group sizes or photos of groups. This test is simple: a man, a shovel, a pile of ammo and a bunch of ARs. What I’m going to do is not really all that safe, and the risk is not just of busting a perfectly good (and expensive) Stoner-type rifle or two. It could lead to injury. But as a wise man once said, “The best lesson is learned from watching the mistakes of others.”

The advocates of piston-driven ARs assert that they are more reliable than the original design. What I’m going to do is relate my experience shoveling dirt on piston-driven ARs and test-firing them, as well as some other, worse tests.

PISTON LINEUP
The rifles included an LWRCI M6A2, an LMT Monolithic Rail Platform, a Ruger SR556C, an S&W M&P15, a Stag Arms M8 and a CMMG M4 clone, all piston driven. Each of them was exactly as it was sent to me, without aftermarket handguards or other accessories. The LWRCI is the latest design, with a one-piece carrier and the expected piston system in a railed, free-float upper. The LMT MRP features a one-piece upper with a piston system instead of a DI gas tube. The S&W M&P15 is a regular, M4-style handguard rifle, with the piston system inside the handguards. The Stag M8 also has plastic handguards, as does the CMMG, which the company (knowing what the test was) shipped to me sans sights.

Some had high-end two-stage triggers, and some had box-stock MIL-SPEC triggers. Some came with sights, others were bare on top. In short, I grossly abused nearly $12,000 worth of primo ARs.


Typically, a new weapons system will be tested by the government, but the old system won’t be tested alongside it. To do so in any good engineering school would get you a flunking grade. (Of course, when the government tested properly in the past, it found out that the “obsolete” 1911A1 was not only more reliable than the desired 9mms, but more accurate as well.)

So, as a baseline, I added two direct gas impingement (DI) rifles to the test: a Rock River Arms Operator Elite and a LaRue OBR 556. Each of them has a tubed handguard, but since the gas tube is simply a means of directing gas and doesn’t move, the handguard style doesn’t matter much.

I’ve buried guns, dunked them, even fired some underwater in the past. I’ve also done a preliminary test on ARs to test my procedure and see what would happen. Back when I was in chemistry lab, the group of us being subjected to the tender mercies of Dr. Crist came up with a description of the status of our lives at that moment: “If we knew what would happen, it wouldn’t be research.” I wasn’t trying to bust guns, but to see where the boundaries of reliable function might exist. So I didn’t stuff the bores full of dirt and shoot them from behind the clubhouse via a long string.


Each rifle was inspected, test-fired and lubed. Three of them had a varied history. I had done a preliminary test like this, and the Stag and the CMMG were survivors of the earlier effort. The LaRue arrived just in time for an LEO five-day patrol rifle class, and in the class I ended up putting around 2,000 rounds through it. So, unlike the others, it received a thorough cleaning and lube before I commenced testing it.

In the interest of keeping things simple and not adding variables, I conducted the test with the kind assistance of Black Hills for ammo and Magpul and CMMG for magazines. I could just imagine the look on Jeff Hoffman’s face when I laid it out for him over the phone: “I deliberately want to make some ARs quit working, and I’d like to do it with your ammo.” And he sent ammo anyway. Magpul and CMMG were happy to send magazines, so I loaded up the war wagon and went off to the secret test range of Gun Abuse Central.

THE TORMENT BEGINS
The first test was simple: I stuffed a loaded magazine in each rifle in turn, closed the dustcover, dropped the rifle on the ground and shoveled some good topsoil onto it -a shovelful onto the receiver and a shovelful onto the handguards to get some in at the piston system. I then picked it up, charged it and fired five rounds.

Then I put the safety on, dropped it (leaving the dustcover open) and shoveled again. I repeated this through three 30-round magazines for each rifle. Obviously, the direct-impingement Rock River Operator Elite and LaRue OBR 556 were utterly unaffected by dirt on the gas tube, but I still shoveled it there so the test procedure wouldn’t deviate.


We’d just had a rain, so the topsoil was good and damp. It clung to the exterior and collected in the corners with great enthusiasm.

The second test was the same, with two changes. I used silty sand instead of topsoil, and I didn’t bother to close the dustcover. I also got a lot less careful with how I put down each rifle. At the start, I had carefully laid down each one. By the time I got to the sand, I simply dropped them and grabbed the shovel. If they bounced over so the dustcover was down, I used the toe of my boot to flip them over.

Degreasing with an aerosol can of brake cleaner did nothing to impede the progress of the piston guns.

They were not babied. The sand collected in places the topsoil had not. Also, as this was on one of the ranges that collects rainwater, the silty sand had a good assortment of empty -sometimes corroded- brass in it.


The lack of excitement was palpable. Sand sprays a bit, but otherwise the rifles worked just fine.

Next I took brake cleaner and hosed the piston system of each rifle to remove any lube that might be there. I then repeated the silty sand test. The Rock River and LaRue DI rifles did not receive the degreasing agent, because the gas tube doesn’t care. There is being complete and then there is being a moron.

The first attempt to oil up the gas system.

With oil to hold it, the sand now clings tightly to every nook and cranny of this LMT MRP, as it did with the other ARs.

I figured that if running dry might be a problem, then running wet would be worse, so I figured I’d make an oily mess of things. My first attempt was to simply pour 10W30 motor oil into the piston of the Ruger. Big mistake. The resulting oily mess was so bad, I didn’t even want to handle it, let alone fire it. After I re-degreased it, I took an oil can and squirted the piston system of each one until they were dripping. And no, I didn’t oil the gas tubes of the two DI rifles. I then went through the sand test one more time.
A point of information here: Oily sand clings to rifles. And it clings to piston systems. When you shoot them dry and sandy, the sand just falls off. But when you fire them oily and sandy, the sand clings until driven off. Oily sand hurts when it is thrown in your face. After the first five-shot test here, I went for a full-face shield. The sand blasted by an oily piston is nothing compared with the fast-flying gunk hurled out of the Rock River muzzlebrake. Brakes are bad enough, but brakes with sand in them are simply awful. The more effective the brake, the more awful it is, and the RRA brake is very effective.

No, they did not stop working. This was becoming intolerable, so I took the Stag, removed the handguard and squirted in more oil. More shoveling and shooting produced the same dismal results. No malfunctions.

UPPING THE ANTE
By this time I was frustrated and decided that I really needed to step up things a bit.


The drum, a bit low, was replenished with water from a scummy drainage pond.

For the last test I took each rifle and dunked it up to the buffer tube retainer in a drum full of scummy, silty pond water out of the nearby drainage pond. The procedure here was simple: Each rifle would be dunked until the bubbles stopped. Then I’d pull it out, pull back the charging handle just an inch or so to break the chamber seal and let water drain (as you are carefully instructed to do in the service). I would then fire five rounds. Then into the water again, and repeat.

Here I had some modest success.

The piston guns, for the first few rounds, the first time dunked, now and then short-stroked. Sometimes. I can only imagine that there was some weird point at which there was enough sand still clinging, but enough oil had been washed off to impede operation. The second dunk washed them clean enough to work 100 percent. The two DI guns, incidentally, worked without a problem.


The oily, sandy AR’s got dunked in the scummy pond water.

At this point in the test, one of the club members was watching in horror. Finally, Wally said, “I can’t take this anymore. You need to go to confession, and I need to go to therapy.”

With the planned test complete, I considered other test materials: talcum powder, ready-mix cement, dry hydraulic fluid, even salt water. Each of these was discounted as either not extreme enough (talcum powder is very fine, but not very hard or abrasive) or just too much (really, ready-mix cement? Who expects a dust cloud of that coming over the horizon?).


Now, since I’d failed in my quest to make any of these rifles cry “uncle,” what have we learned? And no, I do not consider an oily, sand-caked rifle dunked in water and short-stroking now and then as having failed. Well, for one thing, I’d learned that the AR is a lot more reliable than many would think.

As excellent a hunting rifle as it is, I would not want to be shoveling dirt over a Remington Model 742 with the expectation that I would be able to snatch it up out of its dirt-nap and depend on it to whack the next deer that shambled along.

Caliber issues aside, the AR would have no problems in that regard. Lacking a sufficient supply of 6.8, I couldn’t do this test with what many DNR agents would consider a more suitable deer round than 5.56×45.


Oily sand clings everywhere to this Ruger SR556C, and that safety is getting hard and harder to move.

Also, while the sand and sand-and-oil tests were not bad, the dunked-after-sand-and-oil test stage was evil. After the first dunk, many of the rifles became gritty in hand-cycling, and triggers became very stiff. One safety lever seized in place until the silt was later washed out. Silty water is bad, worse than oily glop.

A FINAL CAVEAT
Just in case you’re saying to yourself, “Hey, that sounds cool. Let’s do it at our next tactical match,” may I suggest that you not? I mean it. Don’t do this at home or on the range.


Still working! Sand, dust, gas, brass, everything flies, but this LWRCI M6A2 worked.

Malfunction issues aside, sand or dirt that gets into the bore at the muzzle can seriously harm accuracy, and harm it for good. Water droplets in the bore can also cause long-term problems, especially if there is enough water to “ring” a bore. The dirt sifting into the receiver has to be grinding away at the moving parts, even if there isn’t enough to keep them from functioning.

And what of the two DI control guns? Both worked flawlessly and, lacking a piston to get gunked by oily sand, never failed to operate. While I cringed at the thought of subjecting the ultra- accurate match barrel on the LaRue OBR to this test, I figured it would be a very good chance to see how a match chamber did. It did superbly. .

After adding oil to the sand, things got a bit smoky with this LaRue OBR.

What surprised me were the triggers. Both DI rifles have two-stage match triggers. I was expecting some instances of functional reluctance. There were none.


While I did note a few shots that had heavier-than-expected trigger pulls (from loose sand being sluiced into the lower), they functioned 100 percent. Modern ARs, even those built for match accuracy, work even when subjected to the abuse I was willing to administer.

When it was over, I needed a rest. This test was too much like real work.