I have been fascinated with 80% lowers for a long time.  Having a almost completed lower receiver sent to my door step without the hassle of governmental interference makes a smile on my face from ear to ear.

I know a ton of folks are going to bust my chops but I bought a 80% polymer lower.  Not because I am cheap, but because the polymer lower actually served me best for this specific purpose.

Hear me out.  

Reason No. 1:  I want this rifle to be light weight.  Nothing out there, not even Mag tactical, can compare to the weight savings of a polymer lower.

Reason No. 2:  Polymers are fast to complete.  You do not need any cutting lube and cutting through the material is a breeze.

Reason No. 3:  My lower I bought (James Madison) has some good tech behind it, came with a jig, and cost only $99.99.  If worse comes to worse and this thing does not old up, I will have learned a lesson and will only be out 100 bucks.  Plus, I have never done a 80% lower, so I would prefer working  on a lower that is easy to cut and work on,  


So that is out of the way.

I have all my light weight components picked out and still buying them.  

Here is where I am hung up.

I want a gas piston.  I have never owned or shot using a gas piston and the idea of no carbon build up in the chamber is enough for me to invest without ever using one before.

Adams Arms light weight piston retro kit features a .625 piston gas block for a .625 light weight barrel for about $280.

before considering a gas piston kit, I was looking at JP rifles LMOS BCG or Red X arms titanium BCG.  Both of these BCGs alone cost more then the Adams Arms retro kit, which comes with a carrer.  I would just have to add the bolt, firing pin, ext.

My question is:  Does anyone know how heavy these AA lightweight retro kits actually are?  I know it will be heavier then a light weight BCG but how much more?

Here are the components I have already purchased.

Mega Arms Upper receiver
Voodoo Innovation 16" lite weight .625 barrel
battlecomp minimalist stock
V7 Titanium take down pins, titanium flash hider, titanium end plate, lite weight port door, lite carbine buffer tube
JP rifles Silent Capture spring
BCM KMR 15
V7 KMR titanium barrel nut


I still need a few things like the firing group, grip, charging handle, and whatever else I am missing

No carbon buildup in the chamber "because piston" isn't going to happen. It will run as dirty as any other self loading action.

A self loading rifle opens the bolt early enough in the cycle that once the brass is moved back just a fraction of an inch, the total area open to exhaust gas will be larger than the bore. It will flow gas immediately thru the chamber and into the action.

Blow back? Dirty brass and chamber.  Roller delayed? Dirty brass and chamber. Piston? Dirty brass and chamber. DI? Dirty brass and chamber. Note carefully that the gas in the DI design is routed inside the BCG and exhausts out the two ports in the concave part, out the ejection port. Even more, the gas tube can't force the gas to turn 180 degrees and blow into the chamber.

Pistols cannot and will not keep the chamber clean. That requires the action to remain closed until there is no gas pressure at all, which means there won't be any left to power the action. Making it a manual action gun.

Pistons do foul the gas cylinder just as much as DI does in it's gas cylinder - inside the BCG behind the gas rings. (NOTE - GAS RINGS) It's usually more work to clean them than the AR as they don't tear down as easily. Most are buried under the handguards, I don't see quick disconnect freefloats on the market.

Piston adapter kits are available from vendors like Brownell's. They seem to work ok, you are limiting your source of critical parts to one supplier, and the kit makers and pistol rifle vendors have been going out of business even during the recent panic.

Research the net and find all the information, it will help to have an informed opinion so that you can make a decision with all the facts in hand. If you want piston it can be done, but having a clean chamber isn't one of it's selling points because it's impossible.

AK = piston, right? Here's some posts about corrosive ammo, pistons can't stop it. http://www.calguns.net/calgunforum/showthread.php?t=149826

I get what your saying but I can not help but feel a hard core love for DI systems.  Man I aint trying to convert peoples religion here, and personally I have no problem with DI, every AR I own is DI.....but a piston is something I have to try.

I know you said a piston causes as much fouling as a DI but we can agree to disagree in that respect.  I have seen enough third party testing to know that is simply not the fact.  The only reason I want to try a piston system is to reduce fouling. Here is a old thread from 2010.  http://www.ar15.com/forums/t_3_118/479365_Gas_VS__Piston.html


I am also really confused what you said about the gas rings being buried behind the hand guard?  Im fairly certain I just misunderstood what you said.  And second glance I believe your saying the piston and gas block are buried under that hand guard.

A dirty hand guard will not cause cycling issues, so what is the big deal?  That gas on the hand guard is the same gas being prevented from caking the entire BCG and upper receiver.

You don't really seem to understand exactly how the Stoner gas system (which is not  DI, by the way) works.  The blowback from the chamber exceeds what dribbles out of the gas tube after disengaging the key by many fold.

As Tirod tried to explain to you, they ALL  get dirty in the receiver.  No away around that with an autoloading action.

Why did this turn into a piston/DI debate that wasn't what the OP asked.

In my experience piston system do keep it cleaner how much is debatable. But more importantly they also keep it cooler which can only be a good thing with a poly lower. I have two JMT lowers and and both are holding up very well. One I expect will never give my problems in that it is built into a bullpup configuration that supports the buffer from the upper as well as the lower. The other one well we'll see.

I use two Adams arms piston kits both earlier ones than the lightweight versions so I can't be of any help there good luck with your build.

It has always been my understanding that piston systems are heavier. I know you have to try one but why on an ultralight build? And with carbon buildup in the chamber, clean it, and the "problem" is solved

Thanks for steering this back on track.  Piston, gas tube, whatever.  To each there own.  

I contacted AA about their light weight piston system and no reply yet.  Anyone have a total weight on this system?

Also, does anyone have the weight of JP rifles silent capture carbine length spring?