DI guns are not dirtier than piston. It's a false premise. What the piston offers is the opportunity to ignore cleaning it because it's harder to get to. What a quality DI gun offers is the ease of getting to the "piston assembly" because it's in the bolt carrier.
Both pass gas residue out the chamber on unlocking the bolt, both get residue on the brass and bolt, both still require some cleaning of the action regardless. Anyone who has fired and cleaned a blow back gun, roller locked gun, or piston operated gun knows this fact, but the misconception in AR's about it keeps popping up.
If it's an AR design that is converted to piston, then there are reported issues. True piston guns all control the travel of the bolt with rails, rods, or ways in the bolt and receiver that interlock and prevent the bolt carrier from excessive tilting. A converted AR that doesn't address this isn't fully developed. Take a survey of action designs, it becomes obvious.
There is also the limited market availability of proprietary parts - piston gun makers have already gone out of business. The validity of their design means nothing, it's the viability of their business operation in the world of commerce which failed. They didn't convince enough of us to keep buying. One reason is that for all the benefits that might appear to be available, the notion of price stops us from buying. All the piston guns, like it or not, are competing with the existence of the S&W $650 AR. While some consider it very arguable, the fiscal reality is that paying 100% more for a gun can and will not deliver 100% more accuracy or reliability. The incremental increases are often barely measurable if even detectable in some cases.
That is substantially evidenced by Filthy 14, a carbine class loaner gun that has gone over 50,000 rounds with just oiling, wipedowns, and maybe two actual GI thorough cleanings in it's entire service life. A middle of the road priced DI gun.
A lot of AR builders have looked pistons over, for the money the issue is there's no guarantee of improved performance. The record or documentation simply isn't there. If anything, Delta command sidelined the FN SCAR project they started up precisely because of that reason - the SCAR could not demonstrate it did anything worth the expense over the M4. For all the money, no improvement.
Also goes to the Army cancelling most of the carbine testing program. No quantum leaps going back to piston. All it does it control the timing of the bolt unlocking, it does nothing to make it more accurate or help the soldier get more hits. Hits is what are needed in combat, the weapon is just a bullet launching platform, not the actual instrument that delivers the blow. The bullet does the work, if you want a bigger hit, you launch a bigger bullet, and the service has crew served weapons in use and there to do it.
That's why all the underlying suppositions about piston vs DI are basically just a lot of wrangling over side issues. The DI guns we have are working fine, 45 years after adoption, and there's no demonstrated or documented improvement in all the testing or fielding of piston guns in the last 15 years. Nada. Which substantially nullifies all the old school hate that was birthed in the '60s over a change in warfighting known to be faulty before WWII - that large caliber piston guns were an appropriate tool.
Don't look to the political fallout of our policies, on the battlefield the DI gun delivers, which is why all the older guns are out of service and seconded to irregular forces. Modern armies are copying the record our M16 has established by buying or building them.
People will be arguing piston vs DI for decades to come, the really salient point is that millions have been trained on DI for over 45 years, it works, it's available from dozens of makers, and it's going to be in use for another 45 years. It's going to take a really big leap ahead to find something better, how we unlock the bolt really has little to do with how well a soldier shoots with it. The lighter recoil and having more ammo is what is important. So, why change what is known and proven to work?
Because some just want something different. That goes to image enhancement, not the gritty business of shooting other humans. Different rules apply, which are a subject quite outside piston vs DI.
