Debate

[mrraley]

I've seen it on here a few times and it's been weighing heavy on my mind after I read a few comments lately.

 

So I think it's time to open that can of worms again and see where it goes.... BUT here's the catch.

 

If you are going to make a point, make it a valid point, have something to back it up as proof also. 

 

There will be no he said she said BS. 

 

If this gets off topic, I will have it deleted. 

 

With all that being said, here it is... 

 

Explain to me why or how, a push rod rifle is better than a piston rifle? 

(For some of you, you will understand my opening question and how it is phrased, some will not. So I will clarify it for you.)

 

Explain to me why or how, a (so called) piston rifle is better than (what is called) a direct impingement rifle?

 

If anybody has any questions off line, please PM me. 

 

 

[Sisco]

Good topic! Which I am not qualified to answer, as I assume you are talking exclusively the AR platform. Having owned and owning non AR weapons that are piston designed from the ground up, I really can ascertain no signifigant advantage to piston designs for the way I use my firearms, but I was never in the sandbox, either.  Look forward to reading this discussion.

[survivalshop]

   I really can't say its better or worse ( piston/rod type vs DI  ), but there are advantages & disadvantages to both type systems . 

 

    Depends on your definition of a Piston operating system . You could say the DI system is a Piston system , with the Bolt Carrier being the Piston , with the propellant gas pressure being directed to the Piston ( BCG ) via a length of gas tube .

  

  

[blue109]

From a personal standpoint: I like stuff simple. Between 6 AR style guns I have 2 stock types and 2 handguard systems. One grip. One sling style. If I had 10 more guns they would probably follow the formula. I try to avoid proprietary stuff. People say "more" reliable, but I have no issue with reliability on my standard guns, so "more" reliable than totally reliable seems like a sales pitch.

From a functional standpoint: gas entering the carrier is what begins unlocking the bolt before it slams back.  Not exactly sure if the factory piston setups address this, but the add on kits don't. A little more weight. Few more moving parts. Few more potential failure points. I honestly don't think these things are a huge deal, but worth pointing out.

MY reason for avoiding them is pure preference. I don't think it's any better, Just different.  KISS. don't complicate stuff with complicated stuff. If it ain't broke. Etc.

 

[jtallen83]

The only plus I have found with my P716 is a cooler bolt and I'm not sure that matters much not being a full auto. I was hoping to see the "cleaner running" aspect but I still see plenty of carbon on the outside of the BCG, some of this may be due to running dirty ZQI ammo. I'm starting to see evidence of carrier tilt;

The anodizing is worn off around the buffer retainer with only a few hundred rounds. Several thousand rounds into my AR-10 and there are no wear marks like this.

[GreyGoose]

Plus's and minus's to both of course.

I have both and without going into the minutia of it all, here are my general thoughts;

• DI

1) Free floated barrels, obviously the DI gun lends itself to FF your barrel, and the piston gun has a moving rod connecting the barrel to the action which may affect accuracy.

2) Less moving parts on a DI gun, and when it comes to this stuff less is more, less potential problems.

3) Lighter weight, DI guns are slightly lighter, and we all know under some conditions weight = pain.

4) DI is the standard Mil-Spec configuration, parts are readily available everywhere and interchangeable.

5) DI is more affordable than piston guns.

6) DI require much more care and maintenance.

7) DI guns dump hot, dirty, gas into the BCG and affects reliability.

• PISTON

1) Runs cleaner, resistant to heat, generally more reliable.

2) Less maintenance, tried and true design ie; AK-47

3) Piston guns run better with suppression,

4) Piston guns make better SBR's

5) Less gas blow back in your face.

6)Can run a piston gun longer without lubricating etc. than DI under hard conditions.

7)Piston guns come with adjustable gas block

8)Piston guns are slightly heavier

9)Piston guns use proprietary parts

10)Early piston guns had carrier tilt issues, but that is virtually resolved at this juncture

11)Piston guns are more expensive

I love both, have several DI and only one piston, but I can certainly see why all the elite, top tier, and special forces/ops guys run piston guns.

So, take your pick. ;-)

[98Z5V]

Pat, my opinion is easy - I think that there is one area where the "piston guns" outshine the standard DI system - SBRs running suppressors.  You'll have almost all the gas venting somewhere towards the front, instead of through the bolt carrier and in your face.  IMHO, that is the ONLY situation where I see it as an advantage.  Everything else doesn't matter - on DI guns, you have to clean your bolt tail and inside the carrier.  Piston operation just has that gas venting on or near the gas block, and you have to clean that, too.  Maintenance is maintenance, just two different areas. 

DI works, very well, it's easy to diagnose and modify, and I'll always run them.  If I ever found myself in a situation where the only gun I had was a suppressed SBR, then I'd live with it as a DI gun, but it would be better if it was piston driven.  I don't ever envision myself being in that position, though, where it's gonna be the only thing I ever have...

[Magwa]

I was researching this very thing a while back and I was sold on DI after I saw this video I will never come close to the heat applied to this gun with my semi auto's and if this one can take this abuse it is good enough for me...

[mrraley]

 this is a good list to start with, thank you GreyGoose...

 

BUT

Plus's and minus's to both of course.

I have both and without going into the minutia of it all, here are my general thoughts;

• DI

1) Free floated barrels, obviously the DI gun lends itself to FF your barrel, and the piston gun has a moving rod connecting the barrel to the action which may affect accuracy. true

2) Less moving parts on a DI gun, and when it comes to this stuff less is more, less potential problems. true

3) Lighter weight, DI guns are slightly lighter, and we all know under some conditions weight = pain. partially true... weight also helps reduce felt recoil

4) DI is the standard Mil-Spec configuration, parts are readily available everywhere and interchangeable. correct

5) DI is more affordable than piston guns. true 

6) DI require much more care and maintenance. not necessarily true... you would perform the same amount of maintenance on either rifle.  

7) DI guns dump hot, dirty, gas into the BCG and affects reliability. with proper care and maintenance, this is not a factor. 

• PISTON

1) Runs cleaner, resistant to heat, generally more reliable. false. it does not run cleaner, it just places the carbon and dirt in another location. How would this make it more reliable?

2) Less maintenance, tried and true design ie; AK-47 false. with more moving parts, you have more items to maintain. also false about the AK47. the AK is a true piston, with the AR style being a push rod. The AK's piston is in the gas chamber and is connected to the bolt carrier not like the AR's where it is a floating push rod that hits the top of your bolt carrier.

3) Piston guns run better with suppression, opinion

4) Piston guns make better SBR's  opinion

5) Less gas blow back in your face. true, only due to the fact that it is under your handguard now.

6)Can run a piston gun longer without lubricating etc. than DI under hard conditions. false... still have metal on metal contact which still needs lubrication. 

7)Piston guns come with adjustable gas block 

8)Piston guns are slightly heavier true, equates to the more parts on the rifle

9)Piston guns use proprietary parts true, which equates to the higher pricing. 

10)Early piston guns had carrier tilt issues, but that is virtually resolved at this juncture false, you still and always will have carrier tilt issues. 

11)Piston guns are more expensive true

I love both, have several DI and only one piston, but I can certainly see why all the elite, top tier, and special forces/ops guys run piston guns.

So, take your pick. ;-)

[mrraley]

this is and has been a work in progress. 

I am also working on adding diagrams for actual push rod rifles and AK piston rifles. 

 

But I hope this helps. 

Piston rifles.pdf

[survivalshop]

Nice write up , mrRaley .

[GreyGoose]

Good stuff, thanks for the response mrraley.

BUT

The following is what I would add to that...

• DI

1) Free floated barrels, obviously the DI gun lends itself to FF your barrel, and the piston gun has a moving rod connecting the barrel to the action which may affect accuracy. true Check

2) Less moving parts on a DI gun, and when it comes to this stuff less is more, less potential problems. true Check

3) Lighter weight, DI guns are slightly lighter, and we all know under some conditions weight = pain. partially true... weight also helps reduce felt recoil Yes, it all depends on the point of use what matters more.

4) DI is the standard Mil-Spec configuration, parts are readily available everywhere and interchangeable. correct Check

5) DI is more affordable than piston guns. true Check

6) DI require much more care and maintenance. not necessarily true... you would perform the same amount of maintenance on either rifle.  Not so, the piston will run much longer without having to lubricate, and clean the BCG etc.

7) DI guns dump hot, dirty, gas into the BCG and affects reliability. with proper care and maintenance, this is not a factor. Correct, but that is related to #6

• PISTON

1) Runs cleaner, resistant to heat, generally more reliable. false. it does not run cleaner, it just places the carbon and dirt in another location. How would this make it more reliable? Actually yes and no, they do deposit fouling up in the hand guard area, but its a reduced amount and its effect is far less problematic than all the captured fouling, heat, and dry bolt you get with a DI. Fact is pistons are cleaner and run longer without having to perform maintenance.

2) Less maintenance, tried and true design ie; AK-47 false. with more moving parts, you have more items to maintain. I mentioned that aspect in #2 of the DI section. also false about the AK47. the AK is a true piston, with the AR style being a push rod. The AK's piston is in the gas chamber and is connected to the bolt carrier not like the AR's where it is a floating push rod that hits the top of your bolt carrier. Meh, short stroke vs long stroke is a long debated comparison, PWS has a long stroke piston if you want one in an AR-15 platform.

3) Piston guns run better with suppression, opinion Not opinion, unless you consider common knowledge as opinion

4) Piston guns make better SBR's  opinion See #3

5) Less gas blow back in your face. true, only due to the fact that it is under your handguard now. Okay... but still not in your face! haha

6)Can run a piston gun longer without lubricating etc. than DI under hard conditions. false... still have metal on metal contact which still needs lubrication. 100% true, piston guns will run much much longer without lubrication.

7)Piston guns come with adjustable gas block 

8)Piston guns are slightly heavier true, equates to the more parts on the rifle See #2 in DI

9)Piston guns use proprietary parts true, which equates to the higher pricing. See # 11

10)Early piston guns had carrier tilt issues, but that is virtually resolved at this juncture false, you still and always will have carrier tilt issues. Meh, its a red herring that anti's throw out there, I have never seen it, I don't know anyone who has either, and by the time you have to replace the $30 buffer tube assy you will also have to re-barrel, and relace the BCG! Haha

11)Piston guns are more expensive true Check

[jtallen83]

 

10)Early piston guns had carrier tilt issues, but that is virtually resolved at this juncture false, you still and always will have carrier tilt issues. Meh, its a red herring that anti's throw out there, I have never seen it, I don't know anyone who has either, and by the time you have to replace the $30 buffer tube assy you will also have to re-barrel, and relace the BCG! Haha

 

Just look at the picture I posted above and then you will have seen it...............

It isn't bothering the the buffer tube but it is beating the crap out of the lower receiver just before the tube, a much harder fix. The PWS tube may band-aid this issue as far as not beating up the receiver but it isn't going to stop the carrier tilt.

[GreyGoose]

Just look at the picture I posted above and then you will have seen it...............

It isn't bothering the the buffer tube but it is beating the crap out of the lower receiver just before the tube, a much harder fix. The PWS tube may band-aid this issue as far as not beating up the receiver but it isn't going to stop the carrier tilt.

What year is your gun?

[jtallen83]

What year is your gun?

Born December 30th 2014, I bought it new in June and have less than 400 rounds down the pipe. There are several changes from what Sig shows in the manual or on the web, like the Phase5 buffer tube, but none of those changes address carrier tilt. I think it is just the nature of the beast, there are treatments for the issue but no cure.....yet.

[mrraley]

simple way to check for carrier tilt...

 

Remove your upper from the lower.

With the bolt and bolt carrier in the forward position.

See how much movement your carrier has in the upper receiver.

 

If it has none, great. You have real tight tolerances.  

If it does, great. you just proved that there is carrier tilt when firing your rifle. 

 

Another way to think about it is like this... You have a round object, with NO support except the sleeve around it with an open channel on one side.

In that open channel is a tab. That tab gets hit by a push rod at high velocity. Where's that round object going to go? 

[Magwa]

6) DI require much more care and maintenance. not necessarily true... you would perform the same amount of maintenance on either rifle.  Not so, the piston will run much longer without having to lubricate, and clean the BCG etc.

 

   If you watch the video you will see heat means squat..... the barrel will fail first before the gas tube piston would make no difference rounds down the tube = barrel failure...

[Sisco]

Nice write up Pat. I have an AK and used to have an AR180, both designed from the ground up to be piston rifles. Both were/are incredibly reliable, but really no more than my four AR's. To make a case for piston versus DI would take a useage level and intensity far higher then what I put my weapons through. Plus any time a system is modified to operate in a manner considerably different then its original design, unexpected consequences happen, like carrier tilt. Ask any ordnance engineer. I had an immediate family member who was one, and he made a career out of rectifying those things.Just my uneducated thoughts on the subject.

[GreyGoose]

6) DI require much more care and maintenance. not necessarily true... you would perform the same amount of maintenance on either rifle.  Not so, the piston will run much longer without having to lubricate, and clean the BCG etc.

   If you watch the video you will see heat means squat..... the barrel will fail first before the gas tube piston would make no difference rounds down the tube = barrel failure...

Hey Mag,

Heat certainly affects lubricant life and effective longevity, and the DI gun will begin to fail and stop running long before you shot out the barrel.

Just saying that if you were to stand on the line at a range and shoot them both side by side, they will both run and run, but at some point you will have to stop and service the DI gun before you would the piston. The garbage and heat will eventually dry and foul the BCG in the DI gun and consequently it will begin to experience failures before the piston gun shows those signs, simple as that.

BTW we are trying to get some of PNW guys together this fall, any chance you might make it up this direction for some 308AR comroderie and range time, would luv to meet ya!

Edited September 8, 2015 by GreyGoose

[98Z5V]

GG, you need to research Filthy 14.  It's a DI gun. 

[98Z5V]

Pat, I love how you started that document, right up front.  I knew that's exactly what you were talking about with this statement, in your opener here, too:

Explain to me why or how, a push rod rifle is better than a piston rifle? 

(For some of you, you will understand my opening question and how it is phrased, some will not. So I will clarify it for you.)

I've been preaching that for years - and I've even had people here tell me I'm crazy for saying that, from the gas-rings back to the bolt tail, that IS a piston, and it's in a cylinder (bolt carrier).  The cylinder begins movement, around the piston, in this case, instead of the traditional way where a piston moves inside the stationary cylinder.  People can't get their head around that, and it fuks them all up.

 

[GreyGoose]

GG, you need to research Filthy 14.  It's a DI gun. 

Yep, I know about that one Tom, amazing stuff, but keep in mind they did clean it at least once if I recall as of the last time I checked, and they were constantly lubing it throughout were they not.

Hey guys, I am by no means a DI hater, in fact with DI guns as in most cases in my life I am a traditionalist, I own several DI guns and only the one piston. So my intention is just to admit the foibles where they exist with both gas systems, and without the benefit of regular maintenance, cleaning and lubrication, the piston guns are just less susceptible to failure, I mean that's a pretty well established truth in my own experience, and an accepted fact in the gun community so far as I know.

Doesn't mean piston is better or vise versa, I have documented +'s and -'s with respect to each.

That's all I'm saying, and I think it's hardly a stretch.

[Magwa]

Watch the video they do not lube or clean it is continuous fire till the gun fails and it is NOT the DI that fails it is the barrel and it is full auto fire yep surprised me too I thought for sure the gas tube would fail..... nope!!!! but hey 98 I get it I have always known that the AR 15 ,M16 was a piston gun in a different way ...  I never was a fan of the AK, reliable yes everyone knows that but why make a AR like a AK there is no need the system works fine and has for 55 years . Today with coated BCG's and the great lubes we have there is no reason for a DI to cause any problems. Some say a piston is better for suppressed fire because you can adjust it , well same with adjustable gas block IMO it is a big ta doo about nothing..... IMO...

 

GG, brother watch that video the whole thing it is amazing what the rifle will take  and NO lube.....

Edited September 8, 2015 by Magwa

[survivalshop]

 I was going to point out about that Video , I didn't see anyone clean or lubricate it during the shoot , but it could have been edited ,for all I know . but doubt it .

direct |diˈrekt, dī-|adjective1 extending or moving from one place to another by the shortest way withoutchanging direction or stopping: there was no direct flight that day.• Astronomy & Astrology (of apparent planetary motion) proceeding from west to eastin accord with actual motion.2 without intervening factors or intermediaries: the complications are a direct result of bacteria spreading.   

 

( impinge |imˈpinj|verb (impinges, impinging, impinged) [ no obj. ]have an effect or impact, esp. a negative one: Nora was determined that the tragedy wouldimpingeas little as possible onConstance's life.• advance over an area belonging to someone or something else; encroach: the siteimpinges ona greenbelt area.• (impinge on/upon) Physics strike: the gases impinge on the surface of the liquid.DERIVATIVESimpingement noun.impinger nounORIGIN mid 16th cent.: from Latin impingere ‘drive something in or at,’ fromin- ‘into’ + pangere ‘fix, drive.’ The word originally meant ‘thrust at forcibly,’then ‘come into forcible contact’; hence ‘encroach on’ (mid 18th cent).

 

   I think most don't think of a DI system as a Piston is that there is no direct force onto the Piston as with a forward mounted Piston assembly , not to mention its unconventional Piston system . Most see an internal combustion engine as being the bench mark of what a Piston system is . I see it like a Steam Reciprocating system, with steam piped to a valving system to actuate the piston to force it into motion . In the case of the DI AR rifle system the Steam is replaced with burnt Propellent gases.

   I have never seen a Piston system with the Cylinder that moves vs the Piston  ( The Bolt Carrier or cylinder moves ) (since pistons in general have rings & reciprocate , that's what makes them a Piston ), but who am I to say . I believe the reason they called it a DI system instead of just a Piston system is the way the gas is transferred to the operating system , not that its not a piston system . 

Edited September 8, 2015 by survivalshop

[blue109]

I'm totally down for a steam powered AR.