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Gas piston rifles are all the rage. What value are they, anyhow?

Gas piston rifles are all the rage. What value are they, anyhow?

Last week’s arrival of Ruger’s SR-556 rifle has a certain segment of the shooting community swooning with delight. I’m not at all certain the hoopla is justified.

There are those with the opinion that a gas piston system has merits over the direct gas impingement operation used in the standard M-16/AR-15 family of rifles. There are perceived shortcomings in the impingement system, but in my experience, over many rifles and uncounted thousands of rounds of ammunition, most of the complaints are imagined or overblown.

One supposed problem has to do with the AR-15 gas tube, which leads from the sight block into the upper receiver. That tube, so the detractors say, will get clogged with carbon from the hot combustion gases, and ultimately fail to cycle the action. Frankly, I’ve never seen a tube that had any buildup inside, let alone a clog.

A few weeks back I was helping an acquaintance with some work on his AR-15, and part of the job involved pulling the gas tube out. I inspected the tube, and the inside was shiny clean. Just to prove my point to the gun’s owner, I swabbed the tube with a long, dry pipe cleaner (commonly sold as a “gas tube brush.”) Nothing showed up on the white nap of the cleaner. This is a gun which has been heavily used, to the tune of thousands of rounds of mixed ammunition – and the gas tube had never been touched, yet was still pristine.

This is not to say that the gas tube never develops deposits. If an owner insists on cleaning the gas tube, using any kind of solvent, the residue from that material could carbonize and adhere to the walls of the tube. CLP-type products, which contain oils, would be especially prone to leaving behind soot. I suspect those who complain of dirty gas tubes have done just that, which ironically causes the condition which they’re trying to avoid in the first place!

My solution? I never touch the gas tube, period. I don’t put any oil, bore cleaner, or other liquid into the tube. I’ve found that they stay perfectly clean, no matter how many rounds are fired through, without any attention whatsoever.

Another common complaint is that the gun “defecates where it eats” (though usually the term is somewhat more colorful.) The gas tube outlets in the upper receiver, which supposedly gums up the bolt and leaves deposits in and around the chamber.

Yes, the chamber area does get dirty on the AR-15 – but I can tell you, over many thousands of rounds of shooting both, that it gets no dirtier than an FN-FAL (and is significantly cleaner than any HK rifle.) In our rifle classes, our students will shoot 800 rounds over 2 days; I’ve never seen a chamber area dirty enough to impede functioning.

The bolt itself does get dirtier than on other rifles, but in reality suffers no more than any other system. Again, comparing to the FN-FAL, the area that gets dirty is simply shifted – on the AR-15, it’s the bolt, while on the FAL it’s the gas piston head. Both have to be cleaned with about the same frequency, and failure to do so will induce the same failure in each rifle. To me, it’s a non-issue, because until someone develops a true self-cleaning rifle I’ll be forced to do it myself regardless of the design!

Redesigning the AR-15 with a gas piston, according to supporters, supposedly makes for a more reliable system. I can’t imagine how adding moving parts to any mechanism makes it more reliable, but perhaps there is some new engineering principle which says it can be done. It would certainly be news to me!

I do have significant experience with gas piston designs. I’m a longtime FN-FAL user, having shot many examples and huge amounts of ammunition. In my experience, the gas piston is in fact the weakest point of the whole gun. On the FAL, if the piston is even slightly bent it will bind in the upper receiver boss, and the bolt will not be able to travel forward into battery. Alignment of the gas block and the upper receiver has to be perfect, otherwise binding will occur in one (or sometimes both) places.

I could go on, but my point is that a piston is not necessarily a guarantor of reliability. This, coming from someone who is a huge fan of the FAL!

Ruger’s new gun will probably sell very well to those who believe in the piston concept, but the ironic thing is that Ruger will have to work twice as hard just to equal the reliability of the standard AR-15. First, because more parts doesn’t always translate to better performance, and second because a piston is likely to demand more careful construction and assembly – areas where Ruger, to be fair, does have a bit of a problem.

-=[ Grant ]=-

  • Posted by Grant Cunningham
  • On May 20, 2009

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