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john762

Gas pistons-- smooth or grooved--???

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In the 308--why a smooth (no grooves) piston head? Also, why no "front/on top" vents on the gastube? Where is the gas designed to vent? If the gastube is drilled for vents, would a grooved-head piston better aid the venting process?

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My .223 and 7.62x39 Saiga also have the smooth headed gas pistons. I believe they do this because these are commercial guns and the rings aren't needed. Same thing for the vents in the gas tube. Saves money on labor costs.

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My .223 and 7.62x39 Saiga also have the smooth headed gas pistons. I believe they do this because these are commercial guns and the rings aren't needed. Same thing for the vents in the gas tube. Saves money on labor costs.
What purpose do the rings serve in the original ak-design?--Do they create a "gas turbulance cushion"--reducing friction by centering the piston in the tube? Is the purpose of the vents to reduce "excess" gas pressure during rapidfire? Is the 308 "gas tapoff hole" the same size as other aks? I'd like to think the design engineers in Russia put an appropriate amount of thought into building an ak in the 308 caliber.----REMEMBER MOTHER'S SAYING : Those people wouldn't be placed in a position of authority and responsibility, unless they were capability of doing the job and know what's best for you!----Rocket-Science!! Rocket-Science!!

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On my x39 I replaced the factory piston with a US made one from Hotbarrel (grooved). Also replaced the gas tube with a vented one from an AK. Runs like a scalded dawg!

Some have drilled vent holes in their factory gas tubes and claim their gas system stays cleaner this way.

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The rings do indeed create a turbulent boundary, but not to center the piston in the bore. They act as a "piston ring", reducing blow-by.

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Could I also add a question on the gas tubes, why are some round, like on the valmet I had I in the army, and others are "dimpled". Are they interchangeable? Could I stick a valmet handguard and gastube on a saiga in 7.62x39?

 

Also isn't it better with vents in the tube? Couldn't it create too high a pressure or extra fouling? Or is that only an issue for full auto firing?

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The dimples center the piston in the tube. Different designs for different guns, I personally wouldn't go changing them just for cosmetic reasons.

 

All the factors are part of the overall gun design, and if your gun runs be careful that whatever you change is able to be changed back.

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I think the second part past the piston acts as a carbon scraper. Galil, Valmet, R4 have round tubes w/

star shaped scrapers. AK's have star shaped tubes with a round scraper. It could also just be to help keep the piston centered in the tube as the head is inside the gas block and not cause excessive drag.

maybe both.

Hell, I dono.

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