Hello.  I'm researching doing my first AR-15 pistol build and have a goal of keeping the build exceptionally light weight.

First, I'd like to validate something that seems intuitive to me - most piston systems are going to weigh more than gas tube systems, right?  It seems like a gas tube will weigh less than a piston, but I've been surprised before.  Are there exceptions to this idea?

Can any of you speak to the weight differential I might be looking at doing a piston build vs "DI" build?  I now there are a lot of variables (and I'm still learning about them), but any experience you have would help.  I'm also open to the idea that doing a light weight pistol build isn't going to point me to a piston system.

Also, any pointers for learning more about the best approach for building a piston pistol?  I plan to do some digging into the past posts, so "search the forum" is already on my list.  I'm thinking of resources off AR15.com that you think would be helpful.

Much appreciated!

JIMHO, I think your choice of barrel, optic, rail, and buttstock will have a greater influence on whether it is relatively light, lightweight, exceptionally lightweight, or ridiculously lightweight.

Usually Op Rods are solid rods, as compared to the gas tube, which is a tube, hollow.  So, Op Rods will weigh a few more ounces than a hollow tube.  There are low profile piston gas blocks, so weight-wise, those are on par with a run-of-the-mill DI lo-pro GB.

like I said, just MHO.

If you use a Superlative Arms piston system, you're looking at a 6oz increase unless a similar DI build you compare to has a lighter carrier. The different would be within 1-3 oz if the later wasn't the case.

I have a Superlative Arms 14.5 rifle build that's pretty lightweight without putting plastic or carbon fiber parts. It's weighs ABOuT 5 LBS 5 oz because i modified the piston rod to work with an Adam's Arms lightweight carrier AND because it has a carbine buffer (3 oz) rather than a lightweight one. (it has one of those RBT triggers)

As for your question about a pistol piston. . Well I don't think that even matters at all. . .unless you're running a pistol length gas system, in which you'll either have to get a AA kit or have a Superlative Arms pistol rod modified because there is no mainstream pistol length spec. It doesn't really matter though if you're running a carbine length or above pistol regardless because whether it's a a rifle or list doesn't effect the operation.

Yes, that all makes sense.  Part of my motivation is to build a pistol inspired by the Sig Sauer Rattler which lead me to this neck of the woods.

Thanks for sharing your opinion.

Thank you for pointing me to the Superlative Arms piston system and AA.  I'm just diving into the research and appreciate your thoughts.

I think that the piston system adds some weight of course but I also think that the weight is mostly in the barrel.  There is a reason that the 416 moved to a slimmer profile barrel and to a lesser extent dumped the full picatinny rail but I can say from experience that the original HK quad rail by itself is actually relatively light weight.

the weight difference is negligible. Yes it weighs more but we’re talking a couple ounces. It is a 100% overblown complaint generated by people who overthink things to the extreme.

What you gain is reliability (it’s a tappet, similar to the gas system in the FN FAL, not actually a blast piston like found in the AK) and interior cleanliness. The buffer tube denting issues on early models have long since been resolved as well.

They’re straight up fire. I’m never going back to DI again.