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Old November 14, 2012, 08:09 PM   #14
buckhorn_cortez
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Join Date: July 30, 2010
Posts: 395
Quote:
If you want a piston AR go with Ruger. I think it’s the best value for such a gun on the market and they are pretty close to 100% trouble free.

However I would point out a fact to you and the readership.

In semi-auto guns the piston is a perfect answer to a non-existent problem.
The thing that has caused failures in the M-16 family of rifles and carbine in the US Military’s action is heat. The idea is not valid that the “cleaner piston guns” make them work in sand better. They don’t

The heat from the Stoner system dumps on top of the bolt from the gas key in the carrier. The bolt heats up in full auto fire and in some actions, the amount of FA fire is enough to get the bolt over 900 degrees. I have heard from some folk in Va that it can go even hotter in some cases.
If you take steel and heat it quickly and cool it slowly, and if you do it enough times, you can soften the steel. It’s called annealing.

So, the bolt body gets hot. It cools slowly. It’s hot right where it’s the thinnest, at the cam pin hole. If that gets a bit soft it can elongate in use. Only a few thousandths is enough to make the pin “slap” back and forth as it locks and unlocks. As that continues you see cracks develop at the pin hole. After time the crack can turn into a break, and then you have a weapon failure.

So the piston guns dump the heat outside the action not in the action and the bolt never gets very hot.
Problem solved!
For FULL AUTO!

Note; such a system does NOTHING to keep sand from getting between the bolt and the receiver, so the idea that it’s “better” in the sand is not really true.
You still need to lube them. And lube does attract sand. And the lube will burn off on full auto guns a LOT faster than it does in Semi-auto fire.
So again, the piston gun is a great answer to the problem……IN FULL AUTO!

In Semi autos you CANNOT get the bolt hot enough to soften it without having a LOT of loaded mags, a lot of ammo and a very small brain.

According to the tests we did in Nevada in 2004, firing 10 mags as fast as you could load and shoot an AR-15 (semi-auto of course) in the heat of the day, (in june) and then taking an infrared heat reading on the bolt carrier we found we could not get the bolt and carrier any hotter than 465 degrees. But 4 mags fired full auto in an M-16 got the heat up to 925.
925 will anneal most alloys of steel. 465 will not.

So I make my statement again, that for semi-auto guns the piston is not bad, but it is not doing anything of real value for you that the DI doesn’t do as well.

Also the DI system can be made into a more accurate gun than the piston system just because you can’t totally free-float a piston gun.

Ok……
Your turn.
My turn? You protest too much.

I have a question. You used a non-contact infrared thermometer - did it have an adjustment on it for emissivity? Without the correct emissivity adjustment, you can be 10 F or more off in temperature measurement. Did you adjust the thermometer to the correct emissivity for the surfaces you were measuring?

As for accuracy, I don't consider the AR15 an especially precision rifle. That being said, a friend and I were shooting my REC7 at steel plates using my shooting bag as the rest, and hitting an 8-inch steel plate at 300 yards quite easily.

When I sighted in the scope on the gun, I used the 100 yard tunnel at my gun range to eliminate cross wind problems. The REC7 shot two 5 shot, 3/4-inch groups - I don't need better accuracy than that out of an AR15.

BTW - lubrication cannot "attract sand." It can certainly hold dust, and dirt -but attract it? No. One thing on the Barrett. The bolt is NP3 coated and the gun needs minimal lubrication. I live in New Mexico - it's always dusty, especially on windy days. I use minimal lubrication on REC7 as the gun really doesn't need much. In fact, I haven't lubricated the bolt in the last 1,000 rounds.

There is one advantage to a piston gun even in semi-auto rifles. If you use a supressor on the rifle, a DI rifle requires more lubrication as a larger amount of gas is directed back through the gas tube by the supressor. It is also possible to over gas a DI gun with a supressor. Those problems cannot happen in a piston gun.

The Barrett has a second valve position on the gas block for use with a suppressor and vents more gas out through the block. Without the supressor, the normal gas block setting is self-regulating and does not require an adjustment to run with any type of ammunition.
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