.308 rifle length piston system

None exist as of right now to the best of my knowledge although there are companies working on such conversions including but not limited to Adams Arms (although they have supposedly been working on that conversion for like 5+ years with ZERO progress...at least any hint of availability anytime in the foreseeable future).

If you really NEED (or think you need) a piston operated rifle, do yourself a HUGE favor and buy one that was purpose-designed/built as one and skip the bolt on crap which, even on the .223/5.56 platform rifles, are hit and miss in terms of reliability, etc. And before you ask...NO...you cannot use a .223/5.56 piston conversion on a .308/7.62 rifle. ;)
 
I can only think of problems with such a system, and absolutely no advantages over a DI RLGS.

Anybody else notice that LWRC introduced DI guns at SHOT this year?

Anybody else notice some of the most prominent people in the industry who are behind op-rod driven designs, who also conduct high volume training? Guess what they are shooting in their courses? DI guns.

The amount of rod length, plus port pressures required to run a 7.62 RLGS op-rod system are fighting each other big time. Longer rod = more weight, farther port = less port pressure.

Less port pressure
+
Heavier op-rod weight
=
Short stroking malf-o-matic.