Yeah yeah, you know what I meant. ;)
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I've owned a couple piston ARs (have a couple SCARs as well). I still have one upper but it doesn't see any use. All of my ARs now that I actually use are DI.
My 10.5" LMT is the most reliable SBR I've ever owned. It shoots extremely smooth, feels the same as my 14.5" rifles and works very well suppressed and with a variety of ammo.
I have an 8" PSD in 6.8 that works, but I've never shot it enough to really say. I would NOT buy it again though. I had a 12" MRP that worked also, but it did absolutely nothing better, or really even as well, as a DI 12.5".
The only 10.5" piston AR I've handled was a 416, but it wasn't mine and I only put a couple mags through it. It wasn't the lightest thing but it shot ok.
I haven't bought a piston AR in a number of years and the only reason I bought the MRP was a buddy had it and never fired it, so I took it cheap then sold it not long after.
I've noticed Larry Vickers has commented recently that a piston AR is a good choice for full auto and SBRs. He knows more than I do, but I haven't found any reason to buy a piston 10.5" over a DI 10.5" for me. I run mine hard and suppressed quite often and it hasn't had a single failure in more than a few thousand rounds.
True, but at the same time, it's confusing. People think they need to add a "piston upper" to a AR because it's superior to a "direct impingement system". But in fact, the AR is NOT a direct impingement system and it already has a piston. It's kind of like telling someone their car would work better if they put an engine in it
I have an LMT Direct Impingement AR with a 10.5" barrel that has functioned flawlessly for thousands of rounds. There is absolutely no need to add a piston to an AR, as they run very well when correctly made.
http://farm8.staticflickr.com/7164/6...98b1937f_b.jpg
Since you mentioned dedicated suppressed for the upper, I'd read about Grant's Ultimate Suppressed SBR journey - with a smaller gas port the DI gun can actually have the benefits advertised by the piston guns, but be lighter, simpler, and smoother.
if your doing a dedicated suppressed SBR get a Noveske switchblock.
I have thousands of rounds over the past 3 years, through my Noveske 10.5" (non-switchblock) and M4-2000 combo. I have had no issues with the setup. The bottom line is buy a quality upper, from a quality manufacturer and you will be good to go. By the way, the switchblock is nice.
If you're running a DEDICATED (or semi-dedicated) suppressed SBR.
Get a Colt or BCM M4A1 SOCOM profile barrel (16.1'') and have it cut down, and concentrically re-threaded (and target crowned) by ADCO.
Do not have them open the port. Specifically state that you don't want the port opened. Just to make sure.
They'll do the job right, and you'll end up with a 10.5'' gun with a .062'' port, which I find optimal for function unsuppressed (which will not lock back on the last round in a standard carbine receiver extension but will cycle. In an A5 it should lock back.) but for primarily suppressed use. For referance, I use(d) a .056'' port on a cut down SR-15.
However, most good manufacterers barrels should be good for SBR use.
But if you're never going to shoot it unsuppressed, then having the larger port may be unnecessary.
LMT MPR, buy both a DI barrel and Piston kit