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Posted: 6/12/2013 11:11:15 AM EDT
| I want to build a piston gun. I've read the praises for the HK piston system, but what makes their's different from the SIG and other manufacturers that are engineering piston uppers? Is there a huge drop off in quality from the engineered piston uppers to the piston kits that you install on your barrel? |
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In the past there have been numerous problems with most piston systems out there as they are still relatively new from an engineering perspective and the kinks are still being worked out. Everything from HK's issues with the gas block (and just a rumour I heard once about a batch with buffer/tube galling issues), which based upon the silence recently indicates has been addressed, to LWRCi having trouble with a few of their BCGs losing pieces during the firing cycle, again, seems to have been addressed, or PWS (My preferred AR ATM) with their buffer over travel stop issues (once again, apparently solved). SIG's offering are still too new to have had any detailed feedback be disseminated on them yet. To say that there is a be all and end all of piston systems is like saying there is a be all and end all of DI systems, which there ain't.
Now the VAST majority of the piston systems out there utilize a variation of short stroke system where you have a Hammer rod that takes the gas impulse and uses it to strike itself against the transmission rod that then either strikes a converter rod of some sort (an anti carrier tilt idea, I think) which then hits the BCG, or the transmission rod hits the BCG itself. This system has little springs and vents involved from what I have seen and this leads to lots of little parts to be maintained and cleaned and lost in the field. A few use the long stroke piston system that takes the gas straight from the barrel and drives a one piece or two piece jointed piston rod straight into the BCG either via a hammer idea or by joining the piston to the BCG where the gas key used to go to make the rifle go. To go into real detail will take a book as there are more ideas than there are piston AR manufacturers. Me? I would find the simplest system and build up on that. The fewer moving parts the better, for the most part, in my opinion. Remember, there are no absolutes in this market and I doubt there ever will be. I have used a few of the systems, (HK, PWS, LWRCI, Barrett) and found that I liked the PWS system the best. The reason being is based upon where they derived the piston system from, Kalashnikov. It is simple, robust and reliable. During an evaluation evolution I lubed it up with a lithium lubricant and then put 4000 rounds through it before I was told that was enough. Will every single one of these rifles do this? I'm betting no (the PWS I own privately won't, I know, I tried and it stopped at 2500). But the one in my hands that day did. As a standard, the piston kits you get are not as reliable as the ones that come as a whole rifle. In general the kits are being dropped into an operating environment with a lot of variables, from gas tap diameter differences, chamber to tap distances, barrel lengths, bullet weight, charge weight, muzzle devices, machining tolerances of the original design, buffer tube type, spring weight, buffer mass, etc.. With the ones that come as a whole rifle, they tend to be built around making sure that the piston system will work with the rifle as they have built it. I would say go with a dedicated built from the ground up piston rifle. There are a lot of options out there, I'm sure you're gonna get guys here who have forgotten more about ARs than I will ever know, they'll have a lot more to say on the topic than I. I was just charged with pulling the trigger when the time came. -S. |
The HK system is heavy for a stock rifle out of the box. On top of that its exorbitant price tag doesn't make it worth it in my opinion. On top of that the redesigned magwell is just retarded. Then you need a tool to take it down?  If you want it though go for it. The only thing I really like about the system is the forward venting gas ejection.
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