AR Piston Upper - Not a DI vs. Piston Question

[hk_shootr]

My mk114 Mod 2 has four ports on the bottom of the tube. See the chopsticks, these are the aft ports.
There are two smaller ports about 1.25" forward of this set

[georgeib]

The PWS system dumps the gas under the handguard. The handguard is easy to remove though, so cleaning is simple when it becomes necessary. There is an animation on PWS's homepage that shows the function well: https://www.primaryweapons.com/

[mig1nc]

MCX handguards remove with nothing more than the receiver take down pin.

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[Iraqgunz]

I have heard of the same issues, to include a large agency that was using their stuff.

Interesting. I was going to recommended the exact opposite. That you do NOT consider PWS.

I live in Idaho (formerly Boise) and I own a PWS. Had to have one. Several people I shoot with have one and had to have one as Idaho folk.

Most of us, including myself, have had nothing but trouble with our PWS piston systems. Mostly gas related issues. The overall consensus is the older units are better than the newer.

My first hand experience with their CS left little to be desired.

Mine is the .308 (Mk216) but the others in the group are 5.56.

My 2 cents.







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[Hkbeltfed]

The LWRC, Sig, Adams Arms, et al all dump excess vented gas underneath the handguard/rail.

I thought the big selling point of the Adams Arms was that their system vented back through the barrel and there was no external venting of the system?!?

[ABNAK]

I thought the big selling point of the Adams Arms was that their system vented back through the barrel and there was no external venting of the system?!?

No, it and the LWRC vent in a very similar manner: once the piston moves back far enough to clear the spigot all the excess gas residue spews in a 360 degree fashion (the top of the barrel, the inner sides and top of the handguard/rail). The will also spew forward onto the gas block.

The LWRC does have one saving grace though, it's rail system has a removeable top/front portion which allows for relatively easy access to the residue areas.

[ABNAK]

The PWS system dumps the gas under the handguard. The handguard is easy to remove though, so cleaning is simple when it becomes necessary. There is an animation on PWS's homepage that shows the function well: https://www.primaryweapons.com/

Why would you design a system to blow gas residue directly down onto the barrel? Ruger does that too. Never understood that line of thinking. They couldn't think of a better way/place to blow it out?

To me, having played with enough piston systems over the years to make this observation, my preference would be for a system that expelled gas into the atmosphere forward (somehow) of any handguard/rail. Similar to the HK416 for example.

[ABNAK]

MCX handguards remove with nothing more than the receiver take down pin.

When I had an MCX I took off the handguard and made note of the little black dot where carbon deposited right above the gas exhaust port/piston. I had my buddy mill a hole in the top of the handguard so gas residue would blow right out that hole and not build up underneath the handguard. I have a pic of it in the MCX thread.



(second to the last post on the following page)

https://www.m4carbine.net/showthread...t-an-AR/page42

[georgeib]

As with everything else in life, there are pros and cons with any solution. Venting towards the barrel builds a bit of carbon, but not nearly as much as I would have thought, even after several hundred rounds. Venting upwards through the handguard of the MCX, as in your solution, has its own downsides or Sig would have already implemented it. As does venting forward, as HK does.

Personally, I have no practical objection to PWS's solution. It does bug me that carbon is being deposited on top of the barrel simply because I don't like the idea of it. But in practice, the gas isn't really even that hot, and the carbon is easy enough to clean off every few cases of ammo.

Life is full of compromises, pick one.

[OH58D]

Any idea how the Lewis Machine & Tool piston system vents?