Middy vs Carbine: Does it matter on a piston gun?


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.Scarecrow.
February 7, 2012, 06:00 PM
Does the gas system length matter on a Piston AR? Just in case anyone wants to know, I'm trying to choose an LWRC rifle. Just so you know what system I'm talking about.

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TurtlePhish
February 7, 2012, 06:01 PM
I don't really think it's much different from DI. It essentially works the same, except the gas is acting on the piston rather than the gas key. Middy and rifle are generally smoother than carbine, but I've never shot a piston AR.

JustinJ
February 7, 2012, 06:20 PM
I think LWRC considers the middy to be the better option but don't recall why. In addition to being softer shooting I would venture that the forces acting on the piston, bolt and carrier would be lesser therfore less prone to breakage and possibly longer service life. It will of course be more front heavy. Ultimately i'd ask LWRC.

wally
February 7, 2012, 07:59 PM
On a 16" barrel get the middy so the bayonet lug is in the right place :)

jsimmons
February 9, 2012, 07:56 AM
A mid-length will be less abuisive on the action than a carbine. If you have a choice, go mid-length.

gotigers
February 9, 2012, 08:09 AM
jsimmons said it: less abusinve than a carbine.

If you need a bayonet, it comes in handy. :)

helotaxi
February 9, 2012, 09:03 AM
Because there is no difference in gas tube volume on the piston system between the carbine and middy, the difference in harshness between the two is not nearly as pronounced.

benEzra
February 9, 2012, 10:10 AM
The biggest differences between a middy and a carbine length system will be handguard length and sight radius, for most setups. I like to place my support hand way out front and find that carbine-length handguards are a bit short for me. If you use a close-in grip, it's probably less relevant.
Theoretically, a carbine length piston system will flow hotter gas to the piston, at higher pressure, than a midlength system would. The gas port is presumably sized down in carbine-length piston guns to compensate, but the piston/gas block *might* run a teeny bit hotter. Hard to say without measuring, and the gas block/piston gets too hot to touch regardless of gas system length anyway.

Shawn Dodson
February 9, 2012, 01:41 PM
On a 16" mid-length gas system the distance from the gas port to muzzle is the same as on a 20" rifle.

On a 16" carbine length gas system the distance from the gas port to muzzle is longer - which means the bullet dwells in the bore for a longer period of time after it passes the gas port and exits the muzzle. In addition the distance from the chamber to the gas port is shorter, which means chamber pressures are higher during case extraction.

.Scarecrow.
February 9, 2012, 03:50 PM
Well, the main thing I asked was if it mattered for a piston gun. Got a lot of explanations for the D.I. gun. But no matter, I have chosen the LWRC M6A3.

benEzra
February 9, 2012, 05:55 PM
Well, the main thing I asked was if it mattered for a piston gun. Got a lot of explanations for the D.I. gun.
Both my and Shawn Dodson's comments apply to piston guns too, not just DI guns. As Shawn pointed out a carbine-length piston gun initiates extraction earlier and at a higher pressure than a middy, just as on a DI gun, and for exactly the same reasons.

I see you went with a midlength and I think that's a good choice.

.Scarecrow.
February 10, 2012, 07:19 AM
Ahh okay, Sorry about that Ben and Shawn. I called up LWRC and talked to them about the custom work I wanted done. He said what I wanted would not be possible, while at the same time that M6A3 was looking real pretty, especially to a guy that HATES how Mid-lengths look. Something struck me about that gun though. Really excited for when I get enough cash.

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