The piston-driven AR several years on...

[jakhamr81]

Re: The piston-driven AR several years on...

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Adamxdavis</div><div class="ubbcode-body">

Now, comparing my LWRC to my Armalite Ar-10 and I will say there is no comparison in which gun is easier to maintain and operate. LWRC hands down. My Armalite (gun only .308 cost about $1500)...the LWRC Repr (gun only cost about $3800). The parts, especially the bcg on the lwrc are made better....no doubt about it. Both guns are accurate for their intended shooting distances.



Buy good quality parts in either system and they just work.

I get to go do some sighting work on LWRC's burris fastfire ii sight I have on it....

I love spending money on weapons and ammo with no wife to complain at me about it!

</div></div>

Had you not dropped all of your money on a $3,800 LWRC, you may have had a little more money left over for a better quality optic instead of a Burris Fast Fire

... Just my very humble opinion.

 

[bustin]

Re: The piston-driven AR several years on...

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: eleaf</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: bustin</div><div class="ubbcode-body">
Compare the number of highpower shooters using a AR to those using a M1A and then ask yourself why.
I have had several M1As and double lug M21s, they do not compare with the consistant accuracy of the AR. </div></div>

Which has nothing to do with the accuracy of a DI gun over a piston driven gun.

It's like saying that a single action pistol is better than a double action pistol because "my 1911 .45 outshoots my S&W 357". </div></div>

If you had taken time to read the post of the guy I answered he was saying the M14 was very accurate, I responded to that post. I was shooting piston rifles in a conflict in the mid 80s,
personally owned at least 1 M1a or another for the last 20 years along with a few L1A1 and AR180s not including the hundreds that have passed through the shop. We started testing Sig 556s, SCAR, tested a ACR for a week, LWRC, Adams Arms, PWS as far back as 06. I have shot them personally and believe the results I saw not the hype on the internet. Want a piston rig, buy it I could care less.

 

[adam1122]

Re: The piston-driven AR several years on...

Thanks for the insight....thats just the back up optic for targets inside of 50m. I have a US Optics SN-3 1.8x-10x-37 with illum. reticle and EREK system on the top. Its also got a TBAC 30P-1 on the front alont with Surefire Scout lighting system & IR filter for use with NVG's

I'd be a clown to mount a $350 reflex sight on a DMR rifle wouldnt I? And, everyone on the sight would be like....You have just won the WTF award.

 

[19Scout77]

Re: The piston-driven AR several years on...

Plus you need that Burris just in case you are shooting 1000 yards and one of the playing cards makes a break for it.

 

[bustin]

Re: The piston-driven AR several years on...

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: eleaf</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: boltstop</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: STS</div><div class="ubbcode-body">I don't shoot 3G. But, my home built Adams Arms piston upper in .264 LBC is truly a sub MOA rifle out to 750 yards so far. Inside of 500 yards it 1/2 MOA, all day long if I can keep my form up.
I enjoy the heck out of it. </div></div>

WOW! Impressive. I'm pretty versed in The Language of The Gun, but I've never heard of .264 LBC. Sounds intriguing. I'll have to look it up. What took you in that direction? What do you like/dislike about this caliber (obviously it stays supersonic for a while, lulz)? </div></div>

It's a bastard child of the 6.5 Grendel. </div></div>
Pretty bad when the bastard child is better than what you think the original is. BTW the Grendel wasn't the original, Arne B of CSS had a 6.5 based on a PPC before Alexander came along (the 6.5CSS), Alexander was introduced to Arne by Woody at Lothar Wather because they knew Arne already had a 6.5. Alexander screwed Arne just like everyone else he has come in contact with IMO.
The original 6.5CSS has a .295 neck and a 1.5 degree throat which was a lot more accurate then the Grendels general purpose .300 neck and that weird compound angle throat, the 264 LBC has a .295 neck and 1.5 degree throat just like Arnes 6.5 not like the Grendel so it is really a 6.5CSS clone.

Quote from a article-
"Back in the late 90s Arne Brennan developed a 6.5mm wildcat cartridge based on the 6mm PPC (a cartridge with a well earned reputation as a highly accurate benchrest cartridge). This first generation cartridge spawned a stable of almost identical and, in fact, compatible cartridges. These include the 6.5mm PPCX, 6.5mm BPC and 6.5mm CSS."

 

[adam1122]

Re: The piston-driven AR several years on...

Good one man....nice. I'll give you points on that.

BTW - my ammo is in...so I can begin the zeroing process and then me and my buddy are going to settle up. 175SMK's from SWA....some good looking ammo and it sure aint cheap! If I miss I'll blame it on Mr. Murphy.

 

[excess]

Re: The piston-driven AR several years on...

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Adamxdavis</div><div class="ubbcode-body">BTW - my ammo is in...so I can begin the zeroing process and then me and my buddy are going to settle up. 175SMK's from SWA....some good looking ammo and it sure aint cheap! If I miss I'll blame it on Mr. Murphy.</div></div>

Thanks for the update, we were all on the edge of our seat in anticipation.

 

[pipeinspector]

Re: The piston-driven AR several years on...

You seem to have a lot of experience with these types of rifles, and since you mentioned the Sig 556 I was wondering what was your opinion of them? I know they aren't a traditional AR platform, but they appear to have a lot of features that are attractive to me. Plus the price isn't too bad. I don't have any experience with sig rifles but I have several sig pistols and I have a pretty high opinion of them. I have been considering a new 556, maybe even one in the 7.62 x 39. Thanks.

 

[paulo_santos]

Re: The piston-driven AR several years on...

I have an LMT 556 piston with over 10k rounds and just bought the 6.8 Piston conversion for it. Practical accuracy is the same between DI and Pistons. If you compare equally built AR's the weight is pretty close. I could not tell the difference with the LMT DI and the LMT Piston. There are new Piston AR's that are very lightweight. If you have any carrier tilt issues just get a POF or PWS Enhanced buffer tube. If you look at all of the piston and DI parts, there are pretty much the same amount of parts. And the piston actually replaces one of the weakest parts on the DI, which is the carrier key. So all in all, it is a wash. You pay extra money to have a cleaner running AR. If that is worth it to you, then get a piston AR, if not, then stick with a DI. Either way, who gives a rats ass. It is your money and it is your choice. If you like DI, stick with it. If you like pistons, stick with it. Just go have fun and shoot. It is still an AR.

 

[K_4c]

Re: The piston-driven AR several years on...

heat = failure to springs...

along with the fact that heat also distorts metal and after a period of extended use... heat will cause items on a D.I gun to fail....from your extraction spring to triger springs. I think certain companies (LWRC, POF and LMT to name a few) have made a fine product that flat out works. D.I guns work and they work just fine IF they are maintained... but I'll put my money on a piston gun for reliability (it doesn't shit were it eats).

And as far as these accuracy issues with a piston gun... not sure why they'd be any less accurate then a D.I gun.. bullets out the barrel b4 any of the piston system retracts (unless follow up shoots are affected...but I'm not that hi speed to be able to stack double taps on top of each other)

 

[Sebben]

Re: The piston-driven AR several years on...

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: KChen986</div><div class="ubbcode-body">Here's an interesting test on accuracy done by Molon on M4C:

http://www.m4carbine.net/showthread.php?t=32479&highlight=molon

</div></div>

This test was done incorrectly and gives piston guns a bad name. It has too many variables. The piston set up was touching the hand guard. That makes it not free floating which would cause the accuracy loss. NOT the piston system. I want to see a real test that puts up head to head a Noveske N6 a POF P308 an LWRC REPER and a GAP-10. First at 100 yards doing 10 5 shot groups and 5 10 shot groups indoors with a machine. after that shoot them until they fail. By fail I mean will not shoot any more, stop working, ka-put!

 

[KChen986]

Re: The piston-driven AR several years on...

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Sebben</div><div class="ubbcode-body">
This test was done incorrectly and gives piston guns a bad name. It has too many variables. The piston set up was touching the hand guard. That makes it not free floating which would cause the accuracy loss. NOT the piston system. I want to see a real test that puts up head to head a Noveske N6 a POF P308 an LWRC REPER and a GAP-10. First at 100 yards doing 10 5 shot groups and 5 10 shot groups indoors with a machine. after that shoot them until they fail. By fail I mean will not shoot any more, stop working, ka-put! </div></div>

If only someone had the money, time, and expertise.

 

[scotharr]

Re: The piston-driven AR several years on...

If I wanted a piston, I'd buy a gun purpose-built: like a SIG556, ACR, or scar. Retrofitting an AR will always have drawbacks because the system was purpose-built to be a direct-impingement system. That said, the retrofits seem to work pretty darn good: so next subject.

 

[gstaylorg]

Re: The piston-driven AR several years on...

Pipeinspector,

I have two 556 pistols, three 556 SWATs, and a 556 DMR. The pistols utilize a short stroke piston (same as on the 556 Patrol variants), whereas the 556 SWATs and DMR employ the longer piston. They all have been absolutely reliable once run for a few hundred rounds and properly broken in. The 556 SWATs' accuracy (precision) is average, from 1.5 to 2.0 MOA @ 100 yd, give or take. But that's more than sufficient for the purpose, IMO. They weren't meant to be intermediate/long range precision rifles. The DMR is a little better at MOA to slightly sub-MOA with BH or FGMM match ammo.

Here's a point that may be a little more pertinent to the discussion. The DMR has a single port gas valve (unlike the dual port gas valves on the 556 SWATs and 556 pistols). In position 2, the DMR simply doesn't cycle, because the single port doesn't line up with the gas block port. According to Sig, this was intended to allow the DMR to be fired in single shot mode, more similar to a bolt gun (ie. no cycling to minimize the interference of the piston with accuracy). In my hands, running the DMR in single shot mode yielded tighter SD and ES values for the projectile MVs, but no appreciable difference in accuracy. This was a directly comparable test between cycling vs non-cycling firing mode in the same weapon with the same ammunition.

Now I will acknowledge that I may not be the best shooter on the planet, but my interpretation of this result is that any effect of piston cycling on accuracy of the DMR is not likely to be the limiting effect. In other words, there are other factors that probably affect accuracy of the DMR more significantly than does cycling of the piston system. YMMV.

Every time I see the DI vs piston debate come up, I find myself wondering, does this question even have a real answer? There is no doubt that both systems have their own merits, and with proper maintenance and care, both can be very reliable. So does it really matter to many of us? I'm fortunate that no one is shooting back at me when I go to the range to shoot. Perhaps if they were, I might have a different opinion on the matter. But because they're not, is it really worth arguing whether one is slightly superior to the other? For me it just really isn't that important. JMO.

 

[sobrbiker883]

Re: The piston-driven AR several years on...

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Adamxdavis</div><div class="ubbcode-body"> 175SMK's from SWA....some good looking ammo and it sure aint cheap! If I miss I'll blame it on Mr. Murphy. </div></div>

It ain't cheap? Have you priced the competition for 175 Match ammo? Sothwest is the best price out there for shit as good as it is.


------------------------------------------


Oh, back on topic-my POF in 6.5 Creedmoor dropped a .42moa group and .58moa group when sighting in a couple weeks ago (and I don't shoot groups for shit).

I came in third last weekend at our local match, edged out by 8 points by 6XC boltguns in the breeze.....

Accurate enough for me.

 

[sobrbiker883]

Re: The piston-driven AR several years on...

But to be fair, any DI guns I've seen Scott at Specialized Dynamics screw together shoot as well or better......

 

[adam1122]

Re: The piston-driven AR several years on...

Read the rest of the posts, it has a us optics sn-3 scope 1.8x-10x-37 with erek system, green illuminated reticle, parallax adjustment......oh, and it has a thunder beast 30p-1 can on the front. So no, I didn't get cheap on optics my friend. Don't think I would do to well past 300 m with just a fast fire sight.....

 

[PLeighton]

Re: The piston-driven AR several years on...

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: K_4c</div><div class="ubbcode-body">And as far as these accuracy issues with a piston gun... not sure why they'd be any less accurate then a D.I gun.. bullets out the barrel b4 any of the piston system retracts (unless follow up shoots are affected...but I'm not that hi speed to be able to stack double taps on top of each other)</div></div>
Yes, the bullet is out of the barrel before the action moves, but the moment that the bullet passes the gas port in the barrel the system is pressurized.
With a DI system the gas is just routed to the BCG.
With a GP system the gas pressurizes the piston system which is attached to the barrel.
That pressurized system applies non linear forces on the barrel assembly.
In addition to that, you have barrel harmonics issues at play.

Not trying to continue the argument, just answering your question...

 

[Sebben]

Re: The piston-driven AR several years on...

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Dr. Phil</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: K_4c</div><div class="ubbcode-body">And as far as these accuracy issues with a piston gun... not sure why they'd be any less accurate then a D.I gun.. bullets out the barrel b4 any of the piston system retracts (unless follow up shoots are affected...but I'm not that hi speed to be able to stack double taps on top of each other)</div></div>
Yes, the bullet is out of the barrel before the action moves, but the moment that the bullet passes the gas port in the barrel the system is pressurized.
With a DI system the gas is just routed to the BCG.
With a GP system the gas pressurizes the piston system which is attached to the barrel.
That pressurized system applies non linear forces on the barrel assembly.
In addition to that, you have barrel harmonics issues at play.

Not trying to continue the argument, just answering your question...
</div></div>

I think people are making a bigger deal about it than it really is... Most high quality piston guns are sub MOA anyways. If you are THAT concerned about a difference of maybe 1/4" go get a bolt gun.

 

[Evolution 9]

Re: The piston-driven AR several years on...

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Dr. Phil</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: K_4c</div><div class="ubbcode-body">And as far as these accuracy issues with a piston gun... not sure why they'd be any less accurate then a D.I gun.. bullets out the barrel b4 any of the piston system retracts (unless follow up shoots are affected...but I'm not that hi speed to be able to stack double taps on top of each other)</div></div>
Yes, the bullet is out of the barrel before the action moves, but the moment that the bullet passes the gas port in the barrel the system is pressurized.
With a DI system the gas is just routed to the BCG.
With a GP system the gas pressurizes the piston system which is attached to the barrel.
That pressurized system applies non linear forces on the barrel assembly.
In addition to that, you have barrel harmonics issues at play.

Not trying to continue the argument, just answering your question...
</div></div>

Actually, we don't know that the bullet is out before anything starts to move, and in fact there are strong evidence and arguments to the contrary.

If the pressure doesn't move any parts while the bullet is keeping the system closed, why in the world would parts all of a sudden start moving the instant the bullet leaves the barrel and gives the gases an easier place to go (out the barrel rather than pushing heavy metal parts and springs out of the way)?

There is really no base in logic or physics to say that the parts aren't moving (in fact, they have to be). How far they move is up for discussion, but any movement will affect accuracy.

 

[Sebben]

Re: The piston-driven AR several years on...

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Evolution 9</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Dr. Phil</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: K_4c</div><div class="ubbcode-body">And as far as these accuracy issues with a piston gun... not sure why they'd be any less accurate then a D.I gun.. bullets out the barrel b4 any of the piston system retracts (unless follow up shoots are affected...but I'm not that hi speed to be able to stack double taps on top of each other)</div></div>
Yes, the bullet is out of the barrel before the action moves, but the moment that the bullet passes the gas port in the barrel the system is pressurized.
With a DI system the gas is just routed to the BCG.
With a GP system the gas pressurizes the piston system which is attached to the barrel.
That pressurized system applies non linear forces on the barrel assembly.
In addition to that, you have barrel harmonics issues at play.

Not trying to continue the argument, just answering your question...
</div></div>

Actually, we don't know that the bullet is out before anything starts to move, and in fact there are strong evidence and arguments to the contrary.

If the pressure doesn't move any parts while the bullet is keeping the system closed, why in the world would parts all of a sudden start moving the instant the bullet leaves the barrel and gives the gases an easier place to go (out the barrel rather than pushing heavy metal parts and springs out of the way)?

There is really no base in logic or physics to say that the parts aren't moving (in fact, they have to be). How far they move is up for discussion, but any movement will affect accuracy. </div></div>

Can you say High speed xray cam? If someone has one laying around... I'll lend you my rifle to test haha!

 

[KillShot]

Re: The piston-driven AR several years on...

Lowlight had a discussion with another Hide member about the very same thing, whether or not the bullet has left the barrel before the bolt begins to move. If memory serves me correctly, the BCG is in motion before the bullet has left the barrel. He (Lowlight) may comment on this and correct me if I'm wrong.



<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Sebben</div><div class="ubbcode-body">I think people are making a bigger deal about it than it really is... Most high quality piston guns are sub MOA anyways. If you are THAT concerned about a difference of maybe 1/4" go get a bolt gun.</div></div>


I couldn't agree more.

 

[PLeighton]

Re: The piston-driven AR several years on...

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: KillShot</div><div class="ubbcode-body">Lowlight had a discussion with another Hide member about the very same thing, whether or not the bullet has left the barrel before the bolt begins to move. If memory serves me correctly, the BCG is in motion before the bullet has left the barrel. He (Lowlight) may comment on this and correct me if I'm wrong.</div></div>
In a DI gun the BCG is in motion but it is inline and on the same plane as the bore.
Additionally the bolt is also still locked until the gas is relieved through the ports in the BC.
The momentum from the initial blast powers the BCG as it moves to the end of its travel.

Here is a good thread that discuss this function in great detail:
http://www.snipershide.com/forum/ubbthre...156#Post2448156
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: LFOD1776</div><div class="ubbcode-body">Here's what's going on inside the bolt/carrier...

Gas enters the space between the gas ring on the bolt, and the hole in the BCG through which the firing pin extends. That space is called the cylinder. It's a lot like the cylinder in a car engine.

The gas is under pressure, and hence it exerts a force across the entire inner surface area of that piston. Outside of the receiver, there are only two things that make up that cylinder that can move relative to one-another -- the carrier and the bolt. Inside the receiver, when a shot has been fired, only the carrier can move. That is because the bolt is locked up with the barrel extension.

Thus, the pressure from the gas pushes the carrier backwards. As it moves, the cam unlocks the bolt, and the bolt is yanked back with the carrier. Note that according to the patent (column 3 line 5), illustrated in figure 5, and also in reality, the instant that the carrier begins its rearward travel it is cut off from the gas supply in the barrel, so the pressure in the cylinder and the pressure in the barrel are actually decoupled. The cylinder is pressurized only enough to start the rearward travel of the carrier. So as a practical matter, no equalization can be guaranteed, nor should it be required.

You're right, that the gas key could be a cup instead. In some shape or form, that is essentially how all piston ARs work -- except they're self-cleaning instead of terminating in a little gunk trap.

Unlike the DI system, all piston systems impart torque on the carrier group. I think people call it "carrier tilt". In practice it doesn't seem to stop these piston systems from functioning.

So, why do you ask? </div></div>

 

[scotharr]

Re: The piston-driven AR several years on...

I think 3-gun competitions can be instructional. They are timed events where speed, accuracy, and reliability are key. If you have a malfunction, you are basically out of the running and you are slinging a lot of rounds down range very quickly. The standard, full-length AR still dominates these events almost completely.

http://www.3gunnation.com/news/the_rifle_zero#pagegallery

This says to me that the AR still has the best combination of attributes important for "practical" style shooting. In long range competitions, the AR dominates the event over the M1/M14s in the service rifle category and I can't recall ever seeing any piston driven guns used in the open category: lots of AR-derivatives though.

Theories ultimately have to be proven and competition is one forum to do so: AR-15 still reigns supreme.

 

[K_4c]

Re: The piston-driven AR several years on...

http://www.youtube.com/watch?v=X4Fh-kDnrHo&feature=related

I stand corrected... system does appear to be functioning prior to the bullet leaving the barrel. Your shooting skills better be honed in if you're going to blame a GP rifle for that... If my carbine holds 1.5 moa @ 100 I'm good with that... I didn't buy it to shoot prone. I use it to run and gun. Functionality is key and none of my LWRC products have shit the bed yet.

 

[KillShot]

Re: The piston-driven AR several years on...

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: K_4c</div><div class="ubbcode-body">http://www.youtube.com/watch?v=X4Fh-kDnrHo&feature=related

I stand corrected... system does appear to be functioning prior to the bullet leaving the barrel. Your shooting skills better be honed in if you're going to blame a GP rifle for that... If my carbine holds 1.5 moa @ 100 I'm good with that... I didn't buy it to shoot prone. I use it to run and gun. Functionality is key and none of my LWRC products have shit the bed yet. </div></div>

And, what exactly are we supposed to see in one second?

 

[K_4c]

Re: The piston-driven AR several years on...

just working with what I found.... slight bit of movement is noticed. Doesn't mean much to me other then the gents above stated that my comment is false (and I stand corrected). I'm not an engineer... I just use these tools for their intended purpose.

p.s still a GP fan...

 

[razoredgeknives]

Re: The piston-driven AR several years on...

I was intrigued by the gas piston idea, so I did a lot of reading on it before I build my AR. I also had the Adams arms piston conversion recommended to me by a gunsmith i respect greatly. I recently sold my factory bushmaster, put a little more money into what i got for it, and build my own. I also build my own 6.5 grendel at the same time (now I have the same lower, but 2 different uppers). I have the AA piston system on both uppers. I haven't gotten out and shot them much, but what I have done seems fine... i'll post back later. right now I have my gun apart doing a custom duracoat/cerakote project on it =).

ps. if you are building your own AR, the piston system only costs about $100 more since it includes the gas block, the equivalent of a gas tube (which is the piston itself), a BCG, and the handguards. I have added it up. hope I helped! will post more when I get to really put some rounds through it and abuse it.