I'd go with the SIG 516. OGC had some in stock there was an fde 516 and it was very nice. 

Between the piston and DI, I'd go DI. I have both systems (Stag and an LWRC), and while the piston-operated LWRC does run cooler and cleaner, I've never had my Stag jam from anything other than bad ammo. As Jonjon said, you have to get an AR pretty dirty before she stops on you. If I could only take one AR with me, it would be the Stag. The gas impingement system makes for a lighter gun, and if the BCG breaks for some reason and Stag is no longer in business, I can pretty much buy any BCG out there and be back to shooting again. As far as I know, all the piston systems out there are proprietary, so customer service, adequate supply, repair turnaround time, etc. all need to be factored I much more. Just something to consider.

I would opt for the DD rifle.  For performance I do not prefer an M4/AR design in a forward piston set up.  Many people think it might be nitpicking but I don't like the nose heavy balance on the AR/M4 platform and I don't prefer the recoil impulse either.  But this is preference and most shooters won't notice a big difference in these area's.  There are a few other reasons, but these are the 2 main reasons why I prefer DI vs. piston in this weapon platform.

It is my understanding that other aspects there piston guns would be desireable would be where one would be shooting a range of ammo, shooting auto and shooting suppressed.  At least that's the feedback that I've received from instructors in a few carbine classes that I've gone through.  The last two that most on here wouldn't be doing, at least on a regular basis.  I'd be interested in some of your thoughts on that.

I've had the chance to shoot an HK with auto for a short period in a class and while that's a VERY nice gun, it is pretty heavy.   I was shooting an LMT MRP in that class and that's my heaviest gun.  Overall, they aren't THAT heavy, but when you put them side-by-side with say a DI gun with a light-weight barrel and you're shooting for a whole day, you'll notice it.  At least I did. 

Regarding DI guns being dirty, yeah, I guess they run dirty, but with just a nominal amount of lube, they really don't need that much attention.  Personally, I clean my guns more than I probably need to, but I'm mostly checking for wear on parts along the way more as preventative maintenance than being concerned about keeping them clean.  I've put my guns through multi-day classes with nothing more than a few drops of lube here and there.  Even then, I believe the gun would've kept going without it, but I wanted to make sure I kept the gun lubed. 

Most piston guns are also typically priced higher than the typical quality DI gun.  I'm thinking HK, LWRC and PWS.  That said, if I recall correctly, the SIG 516 was going for about the same price as the DDM4 V5, or maybe slightly more.  Like a few mentioned previously, the piston systems are proprietary for each manufacturer, which does limit your options should something fail. 

I agree that DI guns don't need to be spotless to run, just lubed.  The "white glove" inspection and minimal lube are traditions leftover from the military.  Those conditions and standards do not apply to us civilian shooters, and there has even been more current reports circulating that recommend heavier lubrication rather than minimal.

I never had a problem shooting my AR when I used CLP. Since switching to Fireclean though, the thing runs like a champ and cleaning is minimal.

I agree that DI guns don't need to be spotless to run, just lubed.  The "white glove" inspection and minimal lube are traditions leftover from the military.  Those conditions and standards do not apply to us civilian shooters, and there has even been more current reports circulating that recommend heavier lubrication rather than minimal.

I never had a problem shooting my AR when I used CLP. Since switching to Fireclean though, the thing runs like a champ and cleaning is minimal.

That's some good  stuff!  I'm still using the two small bottles that I got a couple of years ago.  I've actually met one of the founders of the company.  Nice people!  When I ordered, they sent me two sample bottles to distribute to others to test out. 

I've done the "wipe the bolt with paper towel" thing and it really goes get clean enough from just that.  The only part that doesn't really wipe away is the crud that builds up behind the tail of the bolt, but no product is going to prevent that nor does cleaning that area require that much attention/effort. 

Between the piston and DI, I'd go DI. I have both systems (Stag and an LWRC), and while the piston-operated LWRC does run cooler and cleaner, I've never had my Stag jam from anything other than bad ammo. As Jonjon said, you have to get an AR pretty dirty before she stops on you. If I could only take one AR with me, it would be the Stag. The gas impingement system makes for a lighter gun, and if the BCG breaks for some reason and Stag is no longer in business, I can pretty much buy any BCG out there and be back to shooting again. As far as I know, all the piston systems out there are proprietary, so customer service, adequate supply, repair turnaround time, etc. all need to be factored I much more. Just something to consider.

Yeah proprietary parts on a piston gun is a rather big con for me.  Especially now when prices on AR parts have come down significantly, it's nice to be able to use just about any retailer and wait for sales.  I think KAC is one of the few DI guns that uses proprietary parts but that's top of the line stuff.

That's some good  stuff!  I'm still using the two small bottles that I got a couple of years ago.  I've actually met one of the founders of the company.  Nice people!  When I ordered, they sent me two sample bottles to distribute to others to test out. 

I've done the "wipe the bolt with paper towel" thing and it really goes get clean enough from just that.  The only part that doesn't really wipe away is the crud that builds up behind the tail of the bolt, but no product is going to prevent that nor does cleaning that area require that much attention/effort.

The only negative thing I have to say about fireclean, is that it does not work well when used in conjunction with grease.  You really need to follow the instructions and strip off all other lubes and greases on your gun, and the strictly use that product.

I used to be a proponent on using grease on sliding parts (pistol slides, high wear areas on BCG), and traditional oil or lube on everything else.  However, my dad applied fireclean to his slide on this 1911.  I borrowed it for the range one day, and immediately noticed the slide was gummed up and moving like a slow hydraulic piston. A couple drops more drops to the inside of the slide and it was moving like normal again though.

He later told me he had just applied fireclean to the inside without stripping the grease off, and then stored it that way.  Granted, his 1911 has really tight tolerances, but it was enough for me to stop using grease where I normally would.

Hasn't been a problem though.

Yeah proprietary parts on a piston gun is a rather big con for me.  Especially now when prices on AR parts have come down significantly, it's nice to be able to use just about any retailer and wait for sales.  I think KAC is one of the few DI guns that uses proprietary parts but that's top of the line stuff.

I was looking to buy a new BCG for my dad's PWS piston gun, only to find out it was $300 because of the propriety system + attached charging handle. It is a bit of a bummer.

It is my understanding that other aspects there piston guns would be desireable would be where one would be shooting a range of ammo, shooting auto and shooting suppressed.  At least that's the feedback that I've received from instructors in a few carbine classes that I've gone through.  The last two that most on here wouldn't be doing, at least on a regular basis.  I'd be interested in some of your thoughts on that.

I've had the chance to shoot an HK with auto for a short period in a class and while that's a VERY nice gun, it is pretty heavy.   I was shooting an LMT MRP in that class and that's my heaviest gun.  Overall, they aren't THAT heavy, but when you put them side-by-side with say a DI gun with a light-weight barrel and you're shooting for a whole day, you'll notice it.  At least I did. 

Regarding DI guns being dirty, yeah, I guess they run dirty, but with just a nominal amount of lube, they really don't need that much attention.  Personally, I clean my guns more than I probably need to, but I'm mostly checking for wear on parts along the way more as preventative maintenance than being concerned about keeping them clean.  I've put my guns through multi-day classes with nothing more than a few drops of lube here and there.  Even then, I believe the gun would've kept going without it, but I wanted to make sure I kept the gun lubed. 

Most piston guns are also typically priced higher than the typical quality DI gun.  I'm thinking HK, LWRC and PWS.  That said, if I recall correctly, the SIG 516 was going for about the same price as the DDM4 V5, or maybe slightly more.  Like a few mentioned previously, the piston systems are proprietary for each manufacturer, which does limit your options should something fail.

I try to avoid the AR piston vs. AR DI (really a piston and IMO not a true DI system) discussion as much of the info regurgitated is passed on as myth via the written word on the internet and is often not based around first hand experience and factual data / information gained from hands on testing and experience.  Much is propagated by companies touting certain systems as it is to their advantage when it comes to sales.  I will not discount experiences or opinions of other trainers as they may be valid but may not be similar to my own.  Having said that, I do not have any particular hate for AR piston guns with a short stroke op-rod set up, it is just that they are not my preference when it comes to performance and how the weapon handles.  I will also like to note that I am not just some huge AR/M4/M16 fan, as I have a very close and fond relationship with AK pattern rifles also.  Just that everyone that has seen, or knows me, predominantly sees me with the AR/M4.

As for the full auto, I absolutely do not like the recoil characteristic of the short stroke op-rod AR piston set up in comparison to the inline DI system.  I utilize a 10.5" DI select fire M4 and have done heavy testing of all of the conversion type kits up to the dedicated or purpose built M4 type piston rifles / uppers.  I also come across a student base that runs HK416's and even attend closed courses where you see them often.  I have run 416's through entire courses also.  They are great rifles, built like tanks, but heavy like a tank.  I think Stoner had it correct with the inline piston set up in the original design and IME that translates the same in semi auto or select fire.  There is a reason that the AR/M16/M4 pattern rifle has such light, straight to the rear (inline) recoil characteristics due to its design which made it a good evolution in design.

For suppressed, indeed the forward piston set up vents gasses / carbon in a different manner and indeed does keep the action, but this is another topic that is greatly exaggerated on how it actually impacts the performance of the weapon.  However adding more weight as in a suppressor on an already nose heavy rifle is not my choice.  IME a properly set up and quality DI rifle would be my choice even suppressed. 

I will not get into the heat argument as that is simply a silly argument that is easily to disprove by anyone with a simple IR type thermometer or by running the weapons hard side by side and just touching bolts and carriers.  The dirty part, I think there is more than enough info out there on lubrication and how it can keep the AR/M16/M4 running when it is extremely filthy.  Plus it really isn't that hard, even in the field, to pop out a bolt carrier group, wipe it down, lube it up and keep going, for tens upon tens of thousands of rounds.

Lets face it, 99% of shooters have not a darn thing to worry about in how they use their rifles.  Even under worse case conditions / scenario's it is still arguable which might be a better option.  Most people have an intimate relationship with their weapons and will bitterly attempt to justify their purchases, which really is not necessary.  I think people should buy whatever they want but keep a realistic perspective of how they intend to use the weapon.  For myself, I put tens of thousands of rounds through many different set ups and I don't place a higher priority in regards to heat causing failure, excessive build up, etc...I do know that even as much as I shoot with a lot of select fire (I regularily teach this topic also) that a rifle that is of quality parts, put together correctly and is maintained properly, I have no concerns over the piston vs DI argument.  So where do I draw the line?  Weight, recoil characteristics and the bottom line is my own personal performance between the two weapon types.  Carrying and using the rifle for hours on end, or even just as a comparison from drill to drill.  How the weapon handles during recoil, transitionally from target to target and even down to tenths on a timer.  Now for myself I do split hairs.  Granted most shooters will not even come close to noticing these differences in performance, so if they chose to purchase one way or another I am good with that. 

Some here may understand my connection with Sig Sauer and I am not downing the rifle, but simply saying that my preference as a default is not for the AR short stroke op-rod piston system.  I will also mention that if anyone is in Exeter, NH or anywhere training with Sig Sauer, take a note what the other Sig Sauer instructors are running.  Of course they are running Sig Sauer products, but just make note of the DI vs piston in the AR/M16/M4 platform.  Not what they run at certain events, for certain reasons, but what their normal default rifle of choice is.  If I were to chose a piston AR/M4 type rifle, just like any AR/M4 there are definitely much better manufacturers than others.

Again, these are only my opinions and most shooters, especially someone new to this platform, will more than likely not discern any noticeable differences other than in their wallets depending on chosen manufacturer. 

I try to avoid the AR piston vs. AR DI (really a piston and IMO not a true DI system) discussion as much of the info regurgitated is passed on as myth via the written word on the internet and is often not based around first hand experience and factual data / information gained from hands on testing and experience.  Much is propagated by companies touting certain systems as it is to their advantage when it comes to sales.  I will not discount experiences or opinions of other trainers as they may be valid but may not be similar to my own.  Having said that, I do not have any particular hate for AR piston guns with a short stroke op-rod set up, it is just that they are not my preference when it comes to performance and how the weapon handles.  I will also like to note that I am not just some huge AR/M4/M16 fan, as I have a very close and fond relationship with AK pattern rifles also.  Just that everyone that has seen, or knows me, predominantly sees me with the AR/M4.

SNIP

Thank you for the thoughtful response!   

Yeah.  The piston vs DI "discussion" is old and get get heated and like you said, often filled with regurgitation.  Just like my thoughts on the matter are largely from people I've come to accept as SMEs, or at least knowing more than me (which doesn't take much  ).  When I first got into ARs, I had many decisions to make.  DI vs piston.  EoTech vs Aimpoint.  Heavy barrel vs light weight.  Fixed irons vs folding. Etc.  My intention was that I wanted to test them side-by-side and against a shot timer to get to my own conclusions.  Between all of those, I have done my head-to-head tests except for the DI vs piston.  I've been satisfied with DI guns so far, so I can't really get myself to spend the money on a decent piston gun.  Yeah, I've spent (or even wasted) a bunch of money going A vs B testing, but I wanted to know for myself.  I'm also a mod on another gun board and there, I try to state what my personal experience is and what I've read/heard/watched/etc.  At one point, I was even looking into getting some sort of pressure sensor set up to measure recoil impulse to test differences between muzzle devices, piston vs DI, etc.  That never around though.  I've seen some guys post information on the web about that, but I sort of let that go. 

You shoot AKs?  Haha.  I recently bought my first AK in 2012 and it doesn't get much use.  I'd love to get a red dot on it and do some side-by-side with my ARs, but just something that I've been putting off for a while. 

Intersting insight on the full auto and suppressed.  Sadly, an area where I have very limited experience.  I shot another student's DI SBR in a class once and my impression was that it was just really loud.  It functioned well and the weight and length were of course noticeably less/shorter, but I wouldn't consider having an SBR high on my priority given my intended uses.  Now, if I had the option of going suppressed, I think I'd look harder into an SBR to get the overall length down.  But alas, it's just  a wish at this point in Hawaii.  One of my buddies moved to Vegas a little over a year ago and he's pissing me off showing me pics of his SBRs, suppressors, etc.    Haha

I'd still very much would love a good quality piston gun.  I've love an HK, LMT piston, or PWS, but those guns are priced markedly higher than the typical DI guns that I would buy. 

You bring up another topic that comes up often.  Build vs buy complete.  I know you build guns, particularly ARs.  What have you seen with regards to failure rates in built (by shooter themselves) vs manufactured guns?  All of the uppers  that I use for classes are factory complete.  I have a couple of lowers that I built, but those are more project guns.  For classes, I've only used factory assembled guns.  That is what I was recommended and since I haven't had any problems in that regard, I sort of just stayed that course.  I've only had my safety selector break on my LMT.  Other than that, no problems what so ever.  I completely understand the desire men/people have to tinker and want to build things, but I do it more just to understand how everything gets put together. 

You bring up another topic that comes up often.  Build vs buy complete.  I know you build guns, particularly ARs.  What have you seen with regards to failure rates in built (by shooter themselves) vs manufactured guns?  All of the uppers  that I use for classes are factory complete.  I have a couple of lowers that I built, but those are more project guns.  For classes, I've only used factory assembled guns.  That is what I was recommended and since I haven't had any problems in that regard, I sort of just stayed that course.  I've only had my safety selector break on my LMT.  Other than that, no problems what so ever.  I completely understand the desire men/people have to tinker and want to build things, but I do it more just to understand how everything gets put together.

Every manufacturer has experienced problems, however if you look at number of units built / fielded vs. actual failure, you will see a distinctive pattern of percentage failure rates from the various manufacturers.  I often deal heavily with Colt, LMT and FN products and I have seen issues that were related back to the factory.  However those are rare and given the actual numbers of units out the door, failure rate is low.  Components used in assembly of the weapon is first and foremost the biggest consideration.  Next is the actual assembly.  This platform from the assembly perspective is almost akin to Lego's on the outside looking at it, however there are certain area's of the assembly process where knowledge, skill and experience play roles.  In reality of all the work I do, assembling an AR/M4 is about the least complicated.  Having said that, people frequently screw it up when they DIY it.  Often times the hardest part is the correct diagnosis and how to fix the issue if one arises and again this is usually related to poor selection of components.

Many people think that components don't matter so much as they are often sourced from the same manufacturers.  What most fail to realize is that certain companies may require that components meet certain standards in materials, manufacture process and more stringent quality control than others.  So in essence even though many companies that assemble AR/M4's for public consumption may source parts from the same manufacturer, does not mean that all of the parts from those manufacturers are the exact same.  One company might reject certain parts and they could still be sold to other companies.  Or a manufacturer making certain parts may not produce the same part from the exact same materials, tolerances, testing, or quality control from one manufacturer to another. 

As for myself, I have a few AR/M4's that are factory models, but the overall majority of what I own in this platform are built where I source every component that I consider to be the best parts from the best manufacturers.  I do also test and evaluate many many things.  I have confidentiality agreements with several manufacturers / companies and I do provide consultation in many areas in this industry and that is not solely restricted to just for this weapon platform.  Because of this I do get to see and play with a lot of items and I heavily test them out in numerous combinations / configurations.  I do have a set recipe for what I consider to be a high quality / high reliability / high accuracy / hard use weapon.  Because of this I build and run all of my own personally built rifles when I am on my own time.

Again assembly of this weapon is a no-brainer so to speak and where individuals screw up is generally with poor component choice whereas the part itself may cause the problem or in which many poor parts choices in combination create a problem, ie tolerance stacking.  This often makes trouble shooting much more difficult for the lesser experienced DIYer.  Anyone with basic mechanical skills, the correct tools, who can follow directions AND who use quality parts can have great results assembling their own rifles.  In reality people get lucky everyday with poor component choices, but I would not trust those rifles to hard use, or bet my life on them.  I would however suggest those who wish to take a course should ensure that their rifle is of quality parts, assembled correctly and has been completely vetted before taking it through a course.  And have a back up.  So yes a new shooter who is serious about courses is often better served with a quality rifle, from a quality manufacturer.  It sucks paying all that money for travel, course tuition and ammo, only to have your rifle, optic, gear, take a dump on you. 

You shoot AKs?  Haha.  I recently bought my first AK in 2012 and it doesn't get much use.  I'd love to get a red dot on it and do some side-by-side with my ARs, but just something that I've been putting off for a while.

Yep I am an AK guy.  Hell I am just a gun guy.   I have taught Familiarization (FAM FIRE) blocks of instruction for LE and Military for the last several years also and the AK pattern and its close variants from battle rifle to machine gun variants are common.  It is just that most of my stuff seen by others has involved Glocks and AR/M4's.  Those who know me really well are not surprised to see me shooting an AK with a CZ strapped to my side.    But that is rare as I am usually shooting those weapons for fun.  While I have fun shooting in general, 99% of my shooting is business related as opposed to recreational, so the more common weapons I use are those issued to US LE and Military.     

Yep I am an AK guy.  Hell I am just a gun guy.   I have taught Familiarization (FAM FIRE) blocks of instruction for LE and Military for the last several years also and the AK pattern and its close variants from battle rifle to machine gun variants are common.  It is just that most of my stuff seen by others has involved Glocks and AR/M4's.  Those who know me really well are not surprised to see me shooting an AK with a CZ strapped to my side.    But that is rare as I am usually shooting those weapons for fun.  While I have fun shooting in general, 99% of my shooting is business related as opposed to recreational, so the more common weapons I use are those issued to US LE and Military.   

Surf - Mahalo for your insight and wealth of knowledge you provide for us on this 2aHawaii forum we are very fortunate to have you as as a member, you are definitely one who can walk the walk and back up what you say with first hand experience 

I apologize for jacking the thread but wanted to know if you provide firearms instruction to non LE/military types, if not is that something you may be willing to do?

Surf - Mahalo for your insight and wealth of knowledge you provide for us on this 2aHawaii forum we are very fortunate to have you as as a member, you are definitely one who can walk the walk and back up what you say with first hand experience 

I apologize for jacking the thread but wanted to know if you provide firearms instruction to non LE/military types, if not is that something you may be willing to do?

jonjon, I sent you a PM.

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