The other day I was contemplating the various reasons the AR platform has such great accuracy potential when compared to other self loading designs.  What I came up with is the inline actuation possible with the direct gas impingement system. There is no bending torque on the bbl due to bolt carrier activation.  This is also why the AR system can get by with the upper and lower being non-matched parts and the bolt carrier traveling in both pieces.  Only the front of the bolt carrier is semi precisely controlled in it's path.  The rear of the bolt carrier is not a precise fit in the buffer tube.

All this is fine with the direct gas impingement because all the forces are directly inline with the bore.

Now if we convert the AR to gas piston and feed the tappet forces into the top of the bolt carrier we are introducing a downward thrust on the bolt carrier.  The rear of the bolt carrier is going to be thrust downward as it is traversing into the buffer tube.  Is the force of the action spring sufficient to overcome this downward torque ?  Is the offset between the action spring and the tappet small enough that the torque is not a problem?  Are the gas piston upper manufacturers engineering various solutions to this issue ?

rj

It is called carrier tilt.  The LWRC piston guns use a downward sloping key that re-vector the forces to eliminate carrier tilt.  No effects on accuracy.

Quoted: It is called carrier tilt.  The LWRC piston guns use a downward sloping key that re-vector the forces to eliminate carrier tilt.  No effects on accuracy.

It has been acknowledged and addressed by Leitner-Wise, as evidenced by the above post.  Ask Paul about it in the LW forum, and he'll likely talk your ear off in "Physics" lingo.  He talks right over my head...  

Quoted: The other day I was contemplating the various reasons the AR platform has such great accuracy potential when compared to other self loading designs.  What I came up with is the inline actuation possible with the direct gas impingement system. There is no bending torque on the bbl due to bolt carrier activation.  This is also why the AR system can get by with the upper and lower being non-matched parts and the bolt carrier traveling in both pieces.  Only the front of the bolt carrier is semi precisely controlled in it's path.  The rear of the bolt carrier is not a precise fit in the buffer tube. All this is fine with the direct gas impingement because all the forces are directly inline with the bore. Now if we convert the AR to gas piston and feed the tappet forces into the top of the bolt carrier we are introducing a downward thrust on the bolt carrier.  The rear of the bolt carrier is going to be thrust downward as it is traversing into the buffer tube.  Is the force of the action spring sufficient to overcome this downward torque ?  Is the offset between the action spring and the tappet small enough that the torque is not a problem?  Are the gas piston upper manufacturers engineering various solutions to this issue ? rj

40 years tells me direct gas works. Pistons in an AR15 need a few more wars or years proving their mustard before I'll bite

I'm thinking very seriously about getting an LW. I have a friend who swears by his. I would like to check it out and see the differnce first-hand.
Apparently heat is vented out of the system as well, keeping it runing much cooler than DG. Like I said, though, I'd  like to see for myself

Quoted: I'm thinking very seriously about getting an LW. I have a friend who swears by his. I would like to check it out and see the differnce first-hand. Apparently heat is vented out of the system as well, keeping it runing much cooler than DG. Like I said, though, I'd  like to see for myself

Isn't heat what causes pretty much 90% of any reliability problems an AR might have? I THOUGHT it was due to heat murdering the extractor....

heat eats the bolts, extractor, extractor springs and even the mag feed lips.

There is no heat in receiver with gas pistons.

Simon

I'm pretty sure that 55,000psi in the chamber is going to direct some heat at the bolt even in a piston system, though maybe less than a direct gas system. The major problem I see with heat in ARs is that the brass stays stuck to the chamber walls longer as the chamber gets hotter and the extractor starts to either slip, rip through rims, or the bolt short strokes. Even that only happens at extremes of heat or in guns that were marginal to begin with.

I think the real test will be LWs new .308... if they can deliver AR accuracy in a reliable rifle there, that should pretty much settle any conceivable issue I can imagine concerning direct gas v. gas piston.

Onm a semi auto firearm, I doubt that heat is a real issue.

Quoted: No effects on accuracy.

How many offset pistons are winning in F-class, etc competition?

Quoted: Quoted: Quoted: No effects on accuracy. How many offset pistons are winning in F-class, etc competition? How many are being entered?

My guess would be none because the "No effects on accuracy" claim has a very very very small likelyhood of being true...

Quoted: Quoted: Quoted: Quoted: Quoted: No effects on accuracy. How many offset pistons are winning in F-class, etc competition? How many are being entered? My guess would be none because the "No effects on accuracy" claim has a very very very small likelyhood of being true... Or, and more likely, no one who competes has purchased one yet

They should be beating down your door to get one if it does everything you say it does and has no negatives... Heck, just the claimed velocity increase should have serious competitiors lining up to use your system!  

If I had a system like yours that overcame long-proven weaknesses of previous incarnations of the same general idea,  I'd sponsor a few top competitors to get out there *prove* to the world how great it is...

Good point.

I am in line for a POF system.

Quoted: Onm a semi auto firearm, I doubt that heat is a real issue.

In my experience, heat is a big factor.  I've seen a lot of guns that won't go down unless you get them warm, and they don't need to be auto to get that hot, esp in the SW.

Quoted: Quoted: Quoted: Quoted: Quoted: Quoted: No effects on accuracy. How many offset pistons are winning in F-class, etc competition? How many are being entered? My guess would be none because the "No effects on accuracy" claim has a very very very small likelyhood of being true... Or, and more likely, no one who competes has purchased one yet They should be beating down your door to get one if it does everything you say it does and has no negatives... Heck, just the claimed velocity increase should have serious competitiors lining up to use your system!

There ARE lots of us "beating down his door" to get one, and THAT is the reason they are backordered!  

Competition shooters don't go out on a limb with new equipment.  They wait for someone to beat them with it.  Then, they line up to buy it.

Quoted: I guess the real point here is we've all shot the competition, very few have shot ours.  As for sponsoring a few top competitors to *prove* the system, I don't see any cost benefit to such an activity as it's very unlikely to influence the core customer base that we market to.  I'd sooner put the money into hiring more staff to try and get our back order situation under control.

I understand that your target market is mainly interested in "minute of man" performance...  Shooters who pay very close attention to accuracy (ie those who shoot for score) have long ago proven that previous offset piston design are indeed detrimental to accuracy.    Given this, surely you can understand that people tend to take all of your claims with a healthy dose of salt when you claim that your system has "no effects on accuracy"...

Given the claims of increased velocity and no adverse effects on accuracy, I'd expect competitors looking for an edge to be building spaceguns around your offset piston.

Quoted: Maybe, but I don't see your point?

I'm just saying that unsubstantiated marketing claims are counter-productive...    

Are you saying that ALL piston designs are handicapped in the accuracy department

No, I'm saying that as far as I know, in-line pistons like the AR-15 are proven to have an advatage over more traditional offset pistons.  I'm not aware of any accuracy-critical competitions where offset pistons are beating in-line pistons.  If you know of a circuit where offset-pistons are dominating, please enlighten me.

I don't know if your's follows the pattern or not, I was suggesting that if it really breaks the mold, that the best way to prove it would be to get it in the hands of someone who will start winning matches with it.  

What I suggest is that you come and see us and bring your best target DI weapon.  We'll supply ammo, lunch and a selection of our products and we'll shoot them back to back; that way, although it's not scientific, at least you'll have first hand experience and we may capture some interesting data.  What ya say?  It's getting warmer after all.

That would be fun, but my precision rifle would burst into flames if it got within 100 meters of you  (It's a Grendel ).   I may have business in the DC area this summer, if I do, I'll give you a shout.  Where is the range that you frequent located, and how long is it?

Quoted: Quoted: Quoted: I guess the real point here is we've all shot the competition, very few have shot ours.  As for sponsoring a few top competitors to *prove* the system, I don't see any cost benefit to such an activity as it's very unlikely to influence the core customer base that we market to.  I'd sooner put the money into hiring more staff to try and get our back order situation under control. I understand that your target market is mainly interested in "minute of man" performance...  Shooters who pay very close attention to accuracy (ie those who shoot for score) have long ago proven that previous offset piston design are indeed detrimental to accuracy.    Given this, surely you can understand that people tend to take all of your claims with a healthy dose of salt when you claim that your system has "no effects on accuracy"... Given the claims of increased velocity and no adverse effects on accuracy, I'd expect competitors looking for an edge to be building spaceguns around your offset piston. Maybe, but I don't see your point?   Are you saying that ALL piston designs are handicapped in the accuracy department or all AR type piston designs?  You've really lost me.   What I suggest is that you come and see us and bring your best target DI weapon.  We'll supply ammo, lunch and a selection of our products and we'll shoot them back to back; that way, although it's not scientific, at least you'll have first hand experience and we may capture some interesting data.  What ya say?  It's getting warmer after all.

What a great offer!!!

Griz, your even in VA!!!  If a manufacturer ever invited me and I was close, I would be there in a minute!!!  Go test them out and post your results.

Quoted: What a great offer!!! Griz, your even in VA!!!  If a manufacturer ever invited me and I was close, I would be there in a minute!!!  Go test them out and post your results.

It's a very generous offer (but I wouldn't let him to buy lunch), and I seriously hope to take him up on it.   I can't be there in a "minute" though since I'm on the opposite side of the state... It's a 6 hour drive if there is no traffic (last time I had to go to the far side of DC where LW is, construction + NoVa and DC traffic added about 2 hours to that )

Quoted: Quoted: Quoted: Quoted: Quoted: Quoted: No effects on accuracy. How many offset pistons are winning in F-class, etc competition? How many are being entered? My guess would be none because the "No effects on accuracy" claim has a very very very small likelyhood of being true... Or, and more likely, no one who competes has purchased one yet They should be beating down your door to get one if it does everything you say it does and has no negatives... Heck, just the claimed velocity increase should have serious competitiors lining up to use your system!   If I had a system like yours that overcame long-proven weaknesses of previous incarnations of the same general idea,  I'd sponsor a few top competitors to get out there *prove* to the world how great it is...

Yes, yes, that's all very good...but NOT UNTIL MINE'S FINISHED!

Haha.

Quoted: I think it would be worthwhile - we're shooting all the time anyway (tough job but someone has to do it),

It's a helluva lot more fun than sizing gasports for DI guns, R&D'ing flashlights, and gel testing

Please do Griz.  Heaven forbid, a customer just contacted me about doing a conversion on his grendel.  Maybe they can go head to head?  Just bring a standard AA upper.



I am trying to stay positive here, however it is hard to understand your posts as the only claims that are unsubstantiated are yours.  We build and shoot these every day.  So, here is your chance.  Will even hook up the rifle to the air compressor so you can see what happens when the piston cycles.  We put a demonstrator spring on the gas system, and it is quite cool.

The cup leaves the collar in less than a quarter of an inch.  At that point it floats on gas throughout the staged vent.  There is more to it, but if you were truely interested instead of chucking out unsubstantiated theories, you would actually want to find out.  Indirectly it calls our customers liars, noveske and other commercial partners liars, and us liars.  I don't really like it, it is par for the course on this website, but I don't really care that much because these efforts have nothing behind them and don't really have the effect you desire.

We also shot the DPMS AP4 before and after it was retrofitted for piston.  It held a tighter group after but was probably related to the way we set up the gun and the sound suppressor - so you could call it a wash.  The only other thing that was done to effectively change the accuracy of the weapon was we turned the bull barrel down to .750" from the carbine placed journal forward and .850 behind.  Though if this had any effect it would be in the other direction.  Again, just like everything else we have done....no effect on accuracy.

I don't think the piston offers the F class shooter much as they are meticulous with cleaning, replacing parts, spend alot of money on barrels accurizing, etc.  However, it sure is in use and is appreciated in 3 gun.

I don't know if you noticed but ARFCOM or at least the forums you see LW posts are not exactly the domain of the long range high power rifle shooter.  Yes, like you, they are here.  But most would be bored to tears by all of the carbine talk here.  Likewise, I would be bored on one of their sites.







These were all tac drivers, but not the variety that you speak of.  See the focus?

Thanks for your interest though.

Please come up to N.VA.

Ya know, I've always thought it was funny that long range shooters TYPICALLY have bare muzzles, when it has been shown to me over and over that an effective flash suppressor and/or sound suppressor actually INCREASES the accuracy of a rifle.  I understand that they do this by "cleaning up" the gases coming out the front of the barrel and acting on the bullet as it begins its flight.  

Explain that one to me?  

BTW- I think it would be VERY difficult to scientifically prove the effects of the piston, since you'd have to compare the SAME rifle before, and after.  However, "after" also involves fitting the parts to a VERY tight tolerance, therefore possibly affecting accuracy.  Possibly, you'd have to take a rifle, test fire it, then take it apart, put it back together, test fire it, THEN take it back apart, retrofit it with a piston, THEN test fire it.  

I'm a "people-shaped-paper" shooter, so I don't give a rip about sub-MOA differences in accuracy, ONE WAY or the other...  I'll take functionality over accuracy any day.  

Quoted: Please do Griz.  Heaven forbid, a customer just contacted me about doing a conversion on his grendel.  Maybe they can go head to head?  Just bring a standard AA upper.[/qoute] Before and after (like you did with the DPMS) would be more revealing since every barrel shoots differently anyway. I don't think the piston offers the F class shooter much as they are meticulous with cleaning, replacing parts, spend alot of money on barrels accurizing, etc.

My point is that they're always looking for an edge when the wind is blowing.   Getting a velocity increase for free is a huge edge.    Either you're not getting the word out to them or they don't believe you...   I guess it doesn't matter though since you're not interested in that market and can't fill all of your orders anyway.