I haven't read THAT much on the piston system, but here are some observations.  

If you see the water dunking video and some HK propoganda, one can get impressed very fast, but...

It looks to me like having a rod receive a gas impulse which then slams into a as key designed for gas (albeit blunted to take the piston impact) MAY not be the best system.  I would think that the DI, with a blast of gas is pushed rather than slammed metal to metal is optimum for the gun/BCG notwithstanding the heat.  OK, I know people are shooting thousands through their piston guns, and I don't here of bad failures of the BCG, but it is just an observation.  

The SKS uses a similar setup, but the BC is massive, designed for a different purpose (design was from an AA gun?) and semi-auto only.

The AK has the BAR type long rod, which provides a nice push , connected permanently to the setup, designed for full auto, and works well for that purpose.

(I guess too bad I don't have a Valmet).

Back to the AR.  For most of us, living in the US, we CAN clean our guns well.  We're normally not in sandstorms (except for the SW), and don't shoot much full auto. So... maybe the push of the DI system is better.  No?

Pistons don't slam into anything.  The piston rod should already be seated in the bolt carrier prior to firing. I doesn't jump 2 inches forward and smack the bolt carrier as you made it seem.  

I have quite a few piston guns (LMT, LWRC, and a Robinson XCR).  All are a little different in how their piston system is designed and functions.  The Robinson has a long piston and three lug bolt just like an AK.   They are all very reliable and run very clean.

I also own DI guns and they all function just fine as well.   I prefer my pistons anyday to my DI when I have to clean them.  It makes a huge difference.  Lubrication on the bolt and bolt carrier last a lot longer on piston guns since the hot gases and fouling don't wind up in the chamber.

Choose what system you like the most and stick with it.  I like both, but prefer the pistons.

How far does the rod travel to hit the BC?  Thanks.

the rods dont hit the carrier, they should fit flush, they're designed to give the carrier a push.

Just because were able to clean our guns and not have to worry about sand storms doesnt mean that the piston AR system is not suitable for over seas fighting. Look at all the contracts trying to kick out the M4 like the HK 416, or the scar? I know those didnt make it but it wasnt for reliability reasons. And as others have stated, the oprod is seated in the carrier therefor it is not a slam or a hit, but more of a push.

They're already touching the carrier.

Is this the same for kits?

How else is the HK 426 different?  Thanks.

Not only that, but my Adams Arms bolt carrier has what would be the gas key area built into the bolt carrier, so there is nothing to shear off.

SVD and vz58 and G36 and some more use systems with op-rod and short stroke - with no problem. In fact SVD use separate op-rod to improove accuracy.

Using piston system in AR is of course some kind of compromise, but compromise that is directed to get best of AR-world and "piston"-world.



I think that most of us here have ARs not because we need them, but because we want them. What is wrong with wanting to have piston ones??

There is no slamming of the gas pistion into the BCG. There is a contiguous push of the rod on the BCG until the rod hits the end of its travel where the BCG releases away from it. The buffer spring then slams the BCG back into the receiver, just like in a DI. And the process begins again.



Pistons are better because they are proven to be more dependable under adverse conditions and less maintenance (read: way fewer cleaning hours needed) than DI under all conditions, period.