Why do Piston BCGs tilt and DIs don't? - Page 1

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[ARCHIVED THREAD] - Why do Piston BCGs tilt and DIs don't? (Page 1 of 2)

Posted: 3/17/2009 9:12:54 PM EDT

Just wondering why this phenomenon can't be overcome?

Posted: 3/17/2009 9:29:46 PM EDT

[#1]

a piston pushes the gas key portion which is well above the center line. A DI delivers the gas through the key into the bolt area, therefore pushing from the centerline of the bolt straight back.

Posted: 3/17/2009 9:30:52 PM EDT

[#2]

Who says DI bolt carriers don't tilt?

Posted: 3/17/2009 9:38:22 PM EDT

[#3]

Quoted:
Who says DI bolt carriers don't tilt?

The Internet Ninjas!!!! They are like Gremlins, only invisible.

Posted: 3/17/2009 9:40:07 PM EDT

[#4]

Quoted:

Quoted:
Who says DI bolt carriers don't tilt?

The Internet Ninjas!!!! They are like Gremlins, only invisible.

LOL!!!!!!!

Posted: 3/17/2009 9:47:26 PM EDT

[#5]

Quoted:

Quoted:
Who says DI bolt carriers don't tilt?

The Internet Ninjas!!!! They are like Gremlins, only invisible.

LOL!!!!!!!

Yep

Posted: 3/17/2009 9:57:31 PM EDT

[#6]

Quoted:
Who says DI bolt carriers don't tilt?

Posted: 3/17/2009 9:59:43 PM EDT

[#7]

Quoted:

Quoted:
Who says DI bolt carriers don't tilt?

Wow, then I guess we better look at why the buffer tubes wear the way they do.

I mean, if it's not bolt carrier tilt causing the uneven receiver extension wear in high usage weapons it must be something else, eh???

Posted: 3/17/2009 10:12:57 PM EDT

[#8]

http://www.ar15.com/forums/topic.html?b=3&f=66&t=266108

In a DI gun the "piston" inside the bolt carrier is straight in line with the barrel and buffer tube, there is no twisting force on the BC. In a piston AR, the piston strikes the key at the top of the carrier and exerts force off-axis which creates a twisting motion or "tilt" in the carrier.

Posted: 3/17/2009 10:49:49 PM EDT

[#9]

Quoted:
Just wondering why this phenomenon can't be overcome?

The whole carrier tilt phenomenon of piston operated ARs can be managed by using a bolt carrier with a flared rear end. This will lessen the amount a carrier's rear will dive and bite in to the receiver extension, but the trade-off is closer metal to metal clearance. some pics here

Posted: 3/17/2009 11:45:00 PM EDT

[#10]

Is carrier tilt unique to piston AR's only? Do other piston guns like the AK, SIG, FAL etc experience this? If not, why?

Posted: 3/18/2009 1:07:11 AM EDT

[#11]

All piston guns experience torque to the bolt carrier. The tilt is a product of the AR not being originally designed to compensate for this torque so the carrier tilts. Other piston guns such as the SCAR or G36 have rails with long bearing surfaces to keep the carrier inline. It is not hard to eliminate the carrier tilt in the AR. It can be done with skis on the back of the carrier such as HK, LWRC, or the new adams arms carrier or it can be done with an anti-tilt buffer. One of the members here has a patent on one and keeps saying he will get it to market. With either the skis or the modified buffer the result is the same. The force causing the tilt is transmitted to the buffer tube without the carrier tilting. Problem solved. Be sure to lube the buffer tube when using one of these systems as the buffer tube is now your bearing surface. It works great.

Posted: 3/18/2009 5:35:23 AM EDT

[#12]

If it ain't broke don't fix it...

Posted: 3/18/2009 5:45:57 AM EDT

[#13]

The DI AR, does also have a piston… and a cylinder to trap gases to unlock the weapon after a cartridge is fired and unlock the bolt.

The piston is attached to the bottom of the bolt, which fits in the bolt carrier which acts as the gas cylinder(from now referred to as the bolt carrier). The bolt rotates in the cylinder freely, but is limited by the cam pin which is guided in a slot in the bolt carrier.

When the bolt is locked, its cammed rearward and down, when unlocked its forward and upright.

Its all those locking lugs that help maintain a consistent lock up, which is one of the main reasons the AR is as accurate as it is.

The trick to making an auto loading rifle function is getting the bolt to unlock. Most all the early auto loading rifles are unlocked by an operating rod which has a recessed cam area where an extension of the bolt fits. The area is usually shaped the same as the cutout area for the cam pin in the AR bolt carrier. If you have an AK, M1A, M1 Garand, or M1 Carbine I’m sure you know what I’m talking about. When you pull the rod back, the bolt rotates(unlocks). The interesting part is how to use the gas from the spent cartridge to push that operating rod back to unlock the bolt.

In the AR, the operating rod is the gas itself. Instead of a rod in contact with the bolt, gas is diverted from the barrel, down a tube, and directed into the bolt carrier(gas cylinder) directly. When the gas fills the chamber behind the piston it pushes the piston forward (easing unlocking)and the bolt carrier backwards. The piston attached to the bolt stops moving forward when it hits the barrel extension focusing the rest of the gas rearward on the carrier. As the carrier moves backwards, it rotates the bolt by contacting the cam-pin in the groove freeing it to continue rearward until stopped by the recoil spring/buffer.

If you think about it, it’s basically a floating system, which allows for the simple design of the AR. The carrier just moves around in an over sized cylinder. Also – don’t buy into the bullshit about NM carriers being a tighter fit enhancing accuracy, they don’t. The accuracy comes from the consistency of the bolt lock up mentioned above – which has nothing to do with the carrier.

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Anyone who has ever field stripped an auto loading rifle is familiar with a common feature; you didn’t even know the AR doesn’t have or need. All other gas piston operated autoloaders bolts/carriers either ride on grooves milled in the frame, or on rails attached to the receiver of the gun. The AR doesn’t have these, because it doesn’t need them. The Bolt/Carrier system of the AR follows a direct path back and forth which is acted on in line with all the parts. The gas enters from the top, but the pressure is applied inside the cylinder. If you contact the carrier off center it torques/tilts which putts extra stress and wear on the bolt lugs and locking surfaces plus adding stress to parts of the gun that otherwise are not stressed.

Look at all the piston operated auto loaders – the part protruding from the bolt which gets cammed for unlocking are all off center. Without the grooves/rails in the receiver/frame the bolt would be tilting up and down or side to side putting all kinds of wear on the parts and added stress on the bolt and locking lug engagement areas.

I hope this makes sense, I tried to keep it simple. This thread is just about how the AR works. Someone else can start a thread explaining timing, dwell and unlocking issues with the different length barrels and gas port locations. Its not a perfect system. It works better in some applications than others, but all things mechanical are compromises.

Posted: 3/18/2009 6:00:29 AM EDT

[#14]

Let me simplify it for you. Except for the initial movement of the carrier group caused by the gas impingement system, the carrier group moves in a virtual straight line do to inertia. In short stroke piston systems, off-axis forces push on the key for a longer period of time, causing tilt of the BCG. This tilt occurs over a limited period of time, but it is far more than seen in gas impingement.

Posted: 3/18/2009 6:00:38 AM EDT

[#15]

thank you BigBore for posting that explanation again

Posted: 3/18/2009 6:09:12 AM EDT

[#16]

bigbore post = win+/thread.

Just want to say i saw some guy made a buffer with a round protrusion that fit inside the BCG to keep the rear centered in the reciever ext. It was on another forum and dont know if he ever went into production, but maybe something someone could do for themselves, i think the guy pattened it.

Posted: 3/18/2009 6:41:01 AM EDT

[#17]

I wonder if a long stroke piston design would not have the problems of carrier tilt that the short stroke design does.

Posted: 3/18/2009 6:51:00 AM EDT

[#18]

Quoted:
Let me simplify it for you. Except for Including the initial movement of the carrier group caused by the gas impingement system, the carrier group moves in a virtual straight line do to inertia. In short stroke piston systems, off-axis forces push on the key for a longer period of time, causing tilt of the BCG. This tilt occurs over a limited period of time, but it is far more than seen in gas impingement.

So close!

The gas entering the gas key doesn't have the surface area to cause any tilt. It's merely getting redirected into an expansion chamber where it tries to force the bolt and bolt carrier apart.

Posted: 3/18/2009 7:09:32 AM EDT

[#19]

Quoted:

snip

that all needs to be tacked

Posted: 3/18/2009 7:12:55 AM EDT

[#20]

Very nice BigBore! Those are the kind of replies I love reading.

Posted: 3/18/2009 7:14:40 AM EDT

[#21]

the AR-15 bolt carrier group is designed to float in the upper to improve reliability in adverse conditions and ensure that the bolt lugs are loaded as evenly as possible during the firing and unlocking cycle.

adding skis, pads, reducing clearances in the upper, buffers that lock the carrier tail in place, etc all go against the original design intent and are a bad idea.

if you want a piston, start with a gun designed as a piston by a competent engineer or designer.

the AR-15 was not designed to be a piston gun nor is it appropriate to use it as one.

eugene stoner>>> backyard tinkerers and snake oil selling piston companies.

Posted: 3/18/2009 12:22:09 PM EDT

[#22]

I looked for your thread that had all that info in it Bigbore, but apparently it's fallen into the black hole of past-3-months-but-not-yet-archived.

Posted: 3/18/2009 12:51:02 PM EDT

[#23]

Quoted:
I looked for your thread that had all that info in it Bigbore, but apparently it's fallen into the black hole of past-3-months-but-not-yet-archived.

I have it tagged, here it is if you want it:

http://www.ar15.com/forums/topic.html?b=3&f=118&t=403641

Posted: 3/18/2009 1:12:41 PM EDT

[#24]

I hope this makes sense, I tried to keep it simple. This thread is just about how the AR works. Someone else can start a thread explaining timing, dwell and unlocking issues with the different length barrels and gas port locations. Its not a perfect system. It works better in some applications than others, but all things mechanical are compromises.

Well stated. All things mechanical are indeed, compromises. The DI system AR is no different. It has advantages and disadvantages. The main advantage is light weight. The main disadvantage is that powder fouling is vented into the action. Like all machines, it's a compromise that will work for some and not for others.

Posted: 3/18/2009 2:13:03 PM EDT

[#25]

Quoted:
the AR-15 bolt carrier group is designed to float in the upper to improve reliability in adverse conditions and ensure that the bolt lugs are loaded as evenly as possible during the firing and unlocking cycle.

adding skis, pads, reducing clearances in the upper, buffers that lock the carrier tail in place, etc all go against the original design intent and are a bad idea.

.

Good points.

All of which means that if you slightly tweak the buffer tube, everything gets in a bind somewhere through the cycle. If you've ever encountered a bent tube, or a incorrectly made tube that mounted up non-concentric, you'd understand these are bad ideas.

A lot of people have never encountered or thought of these things, and it all seems great...

Take something that is perfect in the stresses are all on a centerline, and then procede to dinking it up, so that you don't have to clean it as much...

Brett

Posted: 3/18/2009 3:32:41 PM EDT

[#26]

Quoted:

Quoted:
I looked for your thread that had all that info in it Bigbore, but apparently it's fallen into the black hole of past-3-months-but-not-yet-archived.

I have it tagged, here it is if you want it:

http://www.ar15.com/forums/topic.html?b=3&f=118&t=403641

That thread needs to be pinned in AR discussions....

Posted: 3/18/2009 4:19:36 PM EDT

[#27]

Great post BigBore, awesome to read about this!

The tilt is a "problem" in the gas piston gun to the extent that it wears on the receiver, but it's not really that much of a problem if you keep an eye on it. Chances are you won't shoot enough ammo to wear our the receiver. Of course, if there were load bearing rails for the bolt carrier to ride on, then the tilt would be naturally counteracted, such as carrier on rails on FAL, G36 and Sig556.

The bottomline is that gas piston is only an after-thought revision to Stoner's original AR design. So to make an AR really adapted for gas piston operation, you'd want an upper with rails and carrier to ride on them. However, that would require steel rails and hence more weight.

Posted: 3/18/2009 4:45:25 PM EDT

[#28]

I do not understand why people who don't shoot suppressed or don't shoot F/A are into Pistons, cleaning a DI upper has never been a problem, and I shoot quite a bit as several members here know.

I guess to each their own and they can choose to spend money as they see fit, I just have yet to find a need for it personally.

Posted: 3/18/2009 7:03:16 PM EDT

[#29]

Quoted:
I do not understand why people who don't shoot suppressed or don't shoot F/A are into Pistons, cleaning a DI upper has never been a problem, and I shoot quite a bit as several members here know.

I guess to each their own and they can choose to spend money as they see fit, I just have yet to find a need for it personally.

Cold, for me it has always been that I don't follow the 'crowd'.... I like being different and having things the way I want it to be, just as many here take their original rifles and add railed forends, lights, bi-pods, ect...just to have a little something different, something their own, something to set them apart from the 'crowd'.

Anyway, I'm not going to war, and hopefully never will see any insurrection inside this great country that so many here think might happen. To me it's just another rifle in my collection...it just happens to be my only AR (right now

), but if things did ever degenerate here that I would find myself needing to use it....well, I hope and pray that never happens.

Cohibra45

Posted: 3/18/2009 7:37:37 PM EDT

[#30]

Quoted:

Quoted:
I do not understand why people who don't shoot suppressed or don't shoot F/A are into Pistons, cleaning a DI upper has never been a problem, and I shoot quite a bit as several members here know.

I guess to each their own and they can choose to spend money as they see fit, I just have yet to find a need for it personally.

Cold, for me it has always been that I don't follow the 'crowd'.... I like being different and having things the way I want it to be,

You know, I can relate to that, and it makes perfect sense, also each person can spend their money as they see fit.

Posted: 3/18/2009 8:01:23 PM EDT

[#31]

Quoted:
the AR-15 bolt carrier group is designed to float in the upper to improve reliability in adverse conditions and ensure that the bolt lugs are loaded as evenly as possible during the firing and unlocking cycle.

adding skis, pads, reducing clearances in the upper, buffers that lock the carrier tail in place, etc all go against the original design intent and are a bad idea.

OK I don’t understand why an anti tilt carrier is a bad idea, locking the carrier tail in place keeps everything in line as it should be without reducing any buffer tube clearance.
I decided not to wait for the guy on M4Carbine.net to release his anti tilt buffer. It’s been in the works for a long time and I decided not to wait for it to come out. Since I have access to a lathe, I made my own by simply modifying an existing buffer by drilling and threading a hole and screwing in a steel T shaped threaded plug. This does not increase the carrier size as the skis do, and now the buffer is the bearing surface so the carrier can not tilt. With a little oil in the buffer tube this should last forever. The AR-15 has the best ergonomics of any battle carbine and a piston makes it better without eating your brass like the Sig 556 or XCR, does. In these difficult economic times stretching the reloading dollar lets you shoot twice as much for the same amount of money with the same reliability of the piston operated 556 or XCR. I’m not slamming the DI AR-15, I know it works, and works great but it is also much more maintenance intensive.
http://img.photobucket.com/albums/v30/Rifleman/AntiTiltBuffer.jpg

Posted: 3/19/2009 9:34:52 AM EDT

[#32]

Quoted:
the AR-15 bolt carrier group is designed to float in the upper to improve reliability in adverse conditions and ensure that the bolt lugs are loaded as evenly as possible during the firing and unlocking cycle.

adding skis, pads, reducing clearances in the upper, buffers that lock the carrier tail in place, etc all go against the original design intent and are a bad idea.

if you want a piston, start with a gun designed as a piston by a competent engineer or designer.

the AR-15 was not designed to be a piston gun nor is it appropriate to use it as one.

eugene stoner>>> backyard tinkerers and snake oil selling piston companies.

Why dont we see premature bolt failure if this is an issue? Reality seems to go against your theory. Should I just ignore the fact that LWRCs dont have a broken bolt problem and just listen to you?

I keep reading all the piston bashers talk about how the bolt will break or the receiver extension will wear out IN THEORY and yet it never happens IN REALITY... why is that?

Posted: 3/19/2009 9:40:14 AM EDT

[#33]

Quoted:
Great post BigBore, awesome to read about this!

The tilt is a "problem" in the gas piston gun to the extent that it wears on the receiver, but it's not really that much of a problem if you keep an eye on it. Chances are you won't shoot enough ammo to wear our the receiver. Of course, if there were load bearing rails for the bolt carrier to ride on, then the tilt would be naturally counteracted, such as carrier on rails on FAL, G36 and Sig556.

The bottomline is that gas piston is only an after-thought revision to Stoner's original AR design. So to make an AR really adapted for gas piston operation, you'd want an upper with rails and carrier to ride on them. However, that would require steel rails and hence more weight.

How many rounds does it take to wear out a piston upper? How many rounds does it take to wear out a DI upper? I noticed these facts are always ignored. I wonder why.... if an upper will outlast 4 barrels who cares about upper life?

Posted: 3/19/2009 9:43:09 AM EDT

[#34]

Quoted:
Quoted:
the AR-15 bolt carrier group is designed to float in the upper to improve reliability in adverse conditions and ensure that the bolt lugs are loaded as evenly as possible during the firing and unlocking cycle.

adding skis, pads, reducing clearances in the upper, buffers that lock the carrier tail in place, etc all go against the original design intent and are a bad idea.

OK I don’t understand why an anti tilt carrier is a bad idea, locking the carrier tail in place keeps everything in line as it should be without reducing any buffer tube clearance.
I decided not to wait for the guy on M4Carbine.net to release his anti tilt buffer. It’s been in the works for a long time and I decided not to wait for it to come out. Since I have access to a lathe, I made my own by simply modifying an existing buffer by drilling and threading a hole and screwing in a steel T shaped threaded plug. This does not increase the carrier size as the skis do, and now the buffer is the bearing surface so the carrier can not tilt. With a little oil in the buffer tube this should last forever. The AR-15 has the best ergonomics of any battle carbine and a piston makes it better without eating your brass like the Sig 556 or XCR, does. In these difficult economic times stretching the reloading dollar lets you shoot twice as much for the same amount of money with the same reliability of the piston operated 556 or XCR. I’m not slamming the DI AR-15, I know it works, and works great but it is also much more maintenance intensive.
http://img.photobucket.com/albums/v30/Rifleman/AntiTiltBuffer.jpg

This is a much better idea than skis since we all know how poorly the HK did with skis in the dust test.

On a more serous note... how does this function propperly to hold the carrier in place yet still allow you to open your upper easily and pop offline? It seems as if it can open easily and pop off it would be easy for the carrier to pop off the raised section during recoil.

Posted: 3/19/2009 9:55:13 AM EDT

[#35]

You just have to pull both pins and slide the upper forward a bit to remove it. No biggie.

It's a neat idea and an elegant solution to the problem, but I've always felt that piston conversions were the proverbial solution to the unasked question. But that's just me.

Posted: 3/19/2009 10:21:31 AM EDT

[#36]

Quoted:
I wonder if a long stroke piston design would not have the problems of carrier tilt that the short stroke design does.

It would not as the forces would still be off center.

Posted: 3/19/2009 10:46:19 AM EDT

[#37]

Quoted:

Quoted:
the AR-15 bolt carrier group is designed to float in the upper to improve reliability in adverse conditions and ensure that the bolt lugs are loaded as evenly as possible during the firing and unlocking cycle.

adding skis, pads, reducing clearances in the upper, buffers that lock the carrier tail in place, etc all go against the original design intent and are a bad idea.

if you want a piston, start with a gun designed as a piston by a competent engineer or designer.

the AR-15 was not designed to be a piston gun nor is it appropriate to use it as one.

eugene stoner>>> backyard tinkerers and snake oil selling piston companies.

Why dont we see premature bolt failure if this is an issue? Reality seems to go against your theory. Should I just ignore the fact that LWRCs dont have a broken bolt problem and just listen to you?

I keep reading all the piston bashers talk about how the bolt will break or the receiver extension will wear out IN THEORY and yet it never happens IN REALITY... why is that?

Reality?

How about this for reality, the only example of an actual military force using piston AR-15s in large enough numbers to matter and they are failing miserably: Norwegian HK416

Not on the range.

Not in training.

In reality.

The "best" piston uppers cant handle ice or dust in combat conditions.... not conjecture or rumor, fact.

Now tell me how your XYZ piston guns have gone through 2000 rounds at your square range and are doing fine. Sweet. Fine. Awesome. A hand full of guns in ideal conditions.

The ONLY large scale users of piston ARs are having major platform wide issues with the bolt carrier group locking up.

Explain that away.

Posted: 3/19/2009 10:49:45 AM EDT

[#38]

Quoted:

Quoted:
I wonder if a long stroke piston design would not have the problems of carrier tilt that the short stroke design does.

It would not as the forces would still be off center.

After reading the entire thread in detail, I now understand the problem. I don't see how it could be overcome without designing a new rifle.

The goal should be to apply force down the centerline of the bolt carrier the way the DI system does. This would require a much different bolt carrier and bolt design than is being used now. Instead of replacing the gas key with an impingement surface for a short stroke piston, you'd want to remove the 'gas key' altogether. You'd replace the gas cylinder in the rear of the bolt with a reinforcemd impingement surface. The oprod would have to angled so that it applied force to the impingement surface. This would give you the centerline application of force. The problem is that the front of the bolt carrier and the bolt would not clear the oprod. I don't see any good way around that without a new, piston only upper receiver.

I suppose your could design a new bolt and bolt carrier that traveled along rails cut on the inside of the upper. This would mitigate the problems of carrier tilt but not eliminate them.

I can only conclude that if you want a gas piston gun, just get an M14, Mini-14, M1 Garand, or Sig 556.

Posted: 3/19/2009 11:06:22 AM EDT

[#39]

Quoted:

Quoted:
the AR-15 bolt carrier group is designed to float in the upper to improve reliability in adverse conditions and ensure that the bolt lugs are loaded as evenly as possible during the firing and unlocking cycle.

adding skis, pads, reducing clearances in the upper, buffers that lock the carrier tail in place, etc all go against the original design intent and are a bad idea.

if you want a piston, start with a gun designed as a piston by a competent engineer or designer.

the AR-15 was not designed to be a piston gun nor is it appropriate to use it as one.

eugene stoner>>> backyard tinkerers and snake oil selling piston companies.

Why dont we see premature bolt failure if this is an issue? Reality seems to go against your theory. Should I just ignore the fact that LWRCs dont have a broken bolt problem and just listen to you?

I keep reading all the piston bashers talk about how the bolt will break or the receiver extension will wear out IN THEORY and yet it never happens IN REALITY... why is that?

Reality?

How about this for reality, the only example of an actual military force using piston AR-15s in large enough numbers to matter and they are failing miserably: Norwegian HK416

One guy on ARFCOM constitutes reality? Hmmm. I'm not convinced pistons on AR's offer much advantage over DI AR's, but once anecdotal poster seems like a bad point-to. For example, is there any indication that the failure was related to being a piston-driven AR?

Not on the range.

Not in training.

In reality.

A number of U.S. military units have used the 416 for evaluation and have generally liked them. Those that have been withdrawn from serive have been done so for reasons of supply, not performance. Crappy H&K customer service to the rescue!

The "best" piston uppers cant handle ice or dust in combat conditions.... not conjecture or rumor, fact.

Unless you could demonstrate that the standard M4 would have done better in teh same conditions (and you can;t), you claim is far-fetched.

Now tell me how your XYZ piston guns have gone through 2000 rounds at your square range and are doing fine. Sweet. Fine. Awesome. A hand full of guns in ideal conditions.

The ONLY large scale users of piston ARs are having major platform wide issues with the bolt carrier group locking up.

Explain that away.

can you point to another source besides a lone ARFCOMer? FWIW, I'm not a huge fan of the HK system. i think there are better, cheaper, and better supported alternatives. Either the LMT or LWRCi solution is superior IMO.

[/quote]

Posted: 3/19/2009 11:16:30 AM EDT

[#40]

Quoted:

Quoted:
the AR-15 bolt carrier group is designed to float in the upper to improve reliability in adverse conditions and ensure that the bolt lugs are loaded as evenly as possible during the firing and unlocking cycle.

adding skis, pads, reducing clearances in the upper, buffers that lock the carrier tail in place, etc all go against the original design intent and are a bad idea.

if you want a piston, start with a gun designed as a piston by a competent engineer or designer.

the AR-15 was not designed to be a piston gun nor is it appropriate to use it as one.

eugene stoner>>> backyard tinkerers and snake oil selling piston companies.

Why dont we see premature bolt failure if this is an issue? Reality seems to go against your theory. Should I just ignore the fact that LWRCs dont have a broken bolt problem and just listen to you?

I keep reading all the piston bashers talk about how the bolt will break or the receiver extension will wear out IN THEORY and yet it never happens IN REALITY... why is that?

Reality?

How about this for reality, the only example of an actual military force using piston AR-15s in large enough numbers to matter and they are failing miserably: Norwegian HK416

One guy on ARFCOM constitutes reality? Hmmm. I'm not convinced pistons on AR's offer much advantage over DI AR's, but once anecdotal poster seems like a bad point-to. For example, is there any indication that the failure was related to being a piston-driven AR?

Not on the range.

Not in training.

In reality.

A number of U.S. military units have used the 416 for evaluation and have generally liked them. Those that have been withdrawn from serive have been done so for reasons of supply, not performance. Crappy H&K customer service to the rescue!

The "best" piston uppers cant handle ice or dust in combat conditions.... not conjecture or rumor, fact.

Unless you could demonstrate that the standard M4 would have done better in teh same conditions (and you can;t), you claim is far-fetched.

Now tell me how your XYZ piston guns have gone through 2000 rounds at your square range and are doing fine. Sweet. Fine. Awesome. A hand full of guns in ideal conditions.

The ONLY large scale users of piston ARs are having major platform wide issues with the bolt carrier group locking up.

Explain that away.

can you point to another source besides a lone ARFCOMer? FWIW, I'm not a huge fan of the HK system. i think there are better, cheaper, and better supported alternatives. Either the LMT or LWRCi solution is superior IMO.

[/quote]

I'm not a fan of HK anything. Their customer service sucks and they charge stupidly high prices for stuff that isn't inherently superior to what we make here in the US. They charge something like $2000 for a semi auto version of the UMP 45. That's personally insulting. That's almost insulting enough for me to call them up and laugh in their faces about it.

Posted: 3/19/2009 11:29:16 AM EDT

[#41]

Quoted:

Quoted:
I wonder if a long stroke piston design would not have the problems of carrier tilt that the short stroke design does.

It would not as the forces would still be off center.

After reading the entire thread in detail, I now understand the problem. I don't see how it could be overcome without designing a new rifle.

I'm not sure I agree. ALL piston guns have to deal with off-center forces. The problem of adapting the AR design to a piston isn't trivial, but it isn't rocket science. For example, plenty of folks are very happy with the performance of the LWRCi guns. Pat Rogers has beaten a few into teh dust and declares himself pleased with the results.

I can only conclude that if you want a gas piston gun, just get an M14, Mini-14, M1 Garand, or Sig 556.

All of those are fine rifles, but I'd pit an LWRCi M6 against any of those.

Is there a need for a Piston AR? I can't answer that. but I can say that I can't see why an AR-derived piston wouldn't work.

Posted: 3/19/2009 12:04:09 PM EDT

[#42]

Quoted:

Quoted:
I wonder if a long stroke piston design would not have the problems of carrier tilt that the short stroke design does.

It would not as the forces would still be off center.

After reading the entire thread in detail, I now understand the problem. I don't see how it could be overcome without designing a new rifle.

I'm not sure I agree. ALL piston guns have to deal with off-center forces. The problem of adapting the AR design to a piston isn't trivial, but it isn't rocket science. For example, plenty of folks are very happy with the performance of the LWRCi guns. Pat Rogers has beaten a few into teh dust and declares himself pleased with the results.

I can only conclude that if you want a gas piston gun, just get an M14, Mini-14, M1 Garand, or Sig 556.

All of those are fine rifles, but I'd pit an LWRCi M6 against any of those.

Is there a need for a Piston AR? I can't answer that. but I can say that I can't see why an AR-derived piston wouldn't work.

I too 'hear' a lot of people saying that the upper and the buffer tube wears out, but no one has any proof or pictures of complete failure of the upper and/or the buffer tube. I called LWRCI and Joe (technical support) was out doing more testing and couldn't answer the phone. I will call be giving a call back tomorrow to talk with them about how many rounds they have shot through their test weapons and if they can supply any information/pictures to help this discussion determine facts.

We need some real information from the people that actually test and shoot these rifles a lot more than others here. Some people here have an agenda to talk down anything with 'piston' and 'AR' in the same sentence. Most people have NO experience with piston ARs, but are just parroting what some others have had with their own personal rifles. That is a very small (and I mean extremely small) sampling to base any knowledge of piston ARs wearing out due to 'tilt'. Pat Rogers has shot many thousands of rounds through piston ARs and has yet to wear out uppers or buffer tubes......

Before anyone can state 'facts', we need to see credentials and pictures. We need to read technical reports by professionals that do the sort of testing for a living. I really wish Doc Roberts would be able to join in with real world information. With his contacts, we could actually get some hard evidence. But as it is, we only get basically hearsay and one off reports damning anything 'AR and piston'!!!

Posted: 3/19/2009 12:10:53 PM EDT

[#43]

Quoted:

Quoted:
I wonder if a long stroke piston design would not have the problems of carrier tilt that the short stroke design does.

It would not as the forces would still be off center.

After reading the entire thread in detail, I now understand the problem. I don't see how it could be overcome without designing a new rifle.

I'm not sure I agree. ALL piston guns have to deal with off-center forces. The problem of adapting the AR design to a piston isn't trivial, but it isn't rocket science. For example, plenty of folks are very happy with the performance of the LWRCi guns. Pat Rogers has beaten a few into teh dust and declares himself pleased with the results.

I can only conclude that if you want a gas piston gun, just get an M14, Mini-14, M1 Garand, or Sig 556.

All of those are fine rifles, but I'd pit an LWRCi M6 against any of those.

Is there a need for a Piston AR? I can't answer that. but I can say that I can't see why an AR-derived piston wouldn't work.

The problem, as several have pointed out, is that the AR was intended to operate as a DI system. There are always issues when making such a massive conversion.

I guess a BCG that rode in rails inside the upper would work though. That's how the long-stroke Garand system works, after all, and it has a reputation for being durable.

I wonder if you could have a bolt with a cutout in the top of it, so that an angled oprod could drop in and impinge on the bolt's centerline. It'd have to be a long stroke design; you'd need to move the bolt and the oprod simultaneously to eliminate bolt / oprod clearance issues. Either that or just make it a *really* long bolt so that the oprod would clear even with the bolt fully opened or closed. That could end up making for a heavy bolt, though. Either likely couldn't fit in a mil-spec dimensioned upper receiver, though. To make it AR system compatible, I think you'd need a BCG that rode in rails.

I've heard good things about LRWCs piston systems. If Pat Rogers likes it, then they must be doing something right somehow.

Another thing to consider: how difficult and expensive is it to replace a buffer tube and bolt carrier? Maybe it's worth it to just replace these components every 5000 rounds or so to prevent issues.

Lots to think about.

Posted: 3/19/2009 12:43:52 PM EDT

[#44]

Quoted:

Quoted:
the AR-15 bolt carrier group is designed to float in the upper to improve reliability in adverse conditions and ensure that the bolt lugs are loaded as evenly as possible during the firing and unlocking cycle.

adding skis, pads, reducing clearances in the upper, buffers that lock the carrier tail in place, etc all go against the original design intent and are a bad idea.

if you want a piston, start with a gun designed as a piston by a competent engineer or designer.

the AR-15 was not designed to be a piston gun nor is it appropriate to use it as one.

eugene stoner>>> backyard tinkerers and snake oil selling piston companies.

Why dont we see premature bolt failure if this is an issue? Reality seems to go against your theory. Should I just ignore the fact that LWRCs dont have a broken bolt problem and just listen to you?

I keep reading all the piston bashers talk about how the bolt will break or the receiver extension will wear out IN THEORY and yet it never happens IN REALITY... why is that?

Reality?

How about this for reality, the only example of an actual military force using piston AR-15s in large enough numbers to matter and they are failing miserably: Norwegian HK416

One guy on ARFCOM constitutes reality? Hmmm. I'm not convinced pistons on AR's offer much advantage over DI AR's, but once anecdotal poster seems like a bad point-to. For example, is there any indication that the failure was related to being a piston-driven AR?

Not on the range.

Not in training.

In reality.

A number of U.S. military units have used the 416 for evaluation and have generally liked them. Those that have been withdrawn from serive have been done so for reasons of supply, not performance. Crappy H&K customer service to the rescue!

The "best" piston uppers cant handle ice or dust in combat conditions.... not conjecture or rumor, fact.

Unless you could demonstrate that the standard M4 would have done better in teh same conditions (and you can;t), you claim is far-fetched.

Now tell me how your XYZ piston guns have gone through 2000 rounds at your square range and are doing fine. Sweet. Fine. Awesome. A hand full of guns in ideal conditions.

The ONLY large scale users of piston ARs are having major platform wide issues with the bolt carrier group locking up.

Explain that away.

can you point to another source besides a lone ARFCOMer? FWIW, I'm not a huge fan of the HK system. i think there are better, cheaper, and better supported alternatives. Either the LMT or LWRCi solution is superior IMO.

He said the Norwegian special forces still use a DI AR-15 (C8 made by Colt Canada) and they are not having the same issues, so yes, it is a piston problem.

To re-cap, you have no technical argument, your argument is that our Norwegian friend Tanfo is a liar. Does that about sum it up?

Posted: 3/19/2009 12:47:50 PM EDT

[#45]

Quoted:

Quoted:
I wonder if a long stroke piston design would not have the problems of carrier tilt that the short stroke design does.

It would not as the forces would still be off center.

After reading the entire thread in detail, I now understand the problem. I don't see how it could be overcome without designing a new rifle.

I'm not sure I agree. ALL piston guns have to deal with off-center forces. The problem of adapting the AR design to a piston isn't trivial, but it isn't rocket science. For example, plenty of folks are very happy with the performance of the LWRCi guns. Pat Rogers has beaten a few into teh dust and declares himself pleased with the results.

I can only conclude that if you want a gas piston gun, just get an M14, Mini-14, M1 Garand, or Sig 556.

All of those are fine rifles, but I'd pit an LWRCi M6 against any of those.

Is there a need for a Piston AR? I can't answer that. but I can say that I can't see why an AR-derived piston wouldn't work.

The problem, as several have pointed out, is that the AR was intended to operate as a DI system. There are always issues when making such a massive conversion.

I'm not sure teh conversion is all that massive. There are issues, to be sure, but ther would be issues with a ground-up piston design as well. Anything made by man has flaws.

I guess a BCG that rode in rails inside the upper would work though. That's how the long-stroke Garand system works, after all, and it has a reputation for being durable.

All teh higher end piston AR makers are building purpose built BCG's designed to deal with the issue, whether it's a "flared" BCG, or one with pads. The LWRC carrier, for example, dove tails in teh key and angles it slightly downward the back end of the BCG has a series of pads to avoid "tilting." Also, it's got a tough nickle-teflon finish which is very slick.

I wonder if you could have a bolt with a cutout in the top of it, so that an angled oprod could drop in and impinge on the bolt's centerline. It'd have to be a long stroke design; you'd need to move the bolt and the oprod simultaneously to eliminate bolt / oprod clearance issues.

You would add a LOT of weight for little benefit IMO. The current gen of piston Ar's seem to deal with teh problem quite effectively. It's just not a huge issue in the latest designs.

I've heard good things about LRWCs piston systems. If Pat Rogers likes it, then they must be doing something right somehow.

There's a bunch of guys over at lightfighter that have them and have put many thousands of rounds downrange with them. The best part is that LWRCi seem genuiniely interssted in constantly improving their product. I bought one and have put a couple hundred through it. Not enough for any kind sample to be sure, but it's a nice gun. Does it offer an advantage over a DI gun? Other than ease of cleaning, not so far. But my DI gun is a Colt 6920 with about 700 rounds flawless rounds through it. How do you get more relaible than 100%? But I'm a low speed high-drag range shooter so far and I haven;t subjected wither gun to harsh conditions yet. Having said that, it's a quality rifle. I'd be pleased with it at the price even if it didn't have the piston.

FWIW, I am taking a Carbine course soon and I'll take the Colt as my primary weapon. My next course, I'll give the M6 a shot. :)

Another thing to consider: how difficult and expensive is it to replace a buffer tube and bolt carrier? Maybe it's worth it to just replace these components every 5000 rounds or so to prevent issues.

I don't think Pat had any problem with carrier tilt in the lowers he used with teh LWRC uppers..... and he put about 20,000 rds through each gun. The uppers underwent an evolution through that time (he started with early model uppers and LWRC updated them as he went along), but the lowers were pretty constant if I recall. You'd think he would have mentioned excessive damage to the lowers.

Lots to think about.

Fun conversation!

Posted: 3/19/2009 12:53:09 PM EDT

[#46]

Quoted:

Well stated. All things mechanical are indeed, compromises. The DI system AR is no different. It has advantages and disadvantages. The main advantage is light weight. The main disadvantage is that powder fouling is vented into the action. Like all machines, it's a compromise that will work for some and not for others.[/div]

The powder gases are exhausted out the two holes in the side of the bolt carrier not into the action.

Posted: 3/19/2009 12:55:08 PM EDT

[#47]

Look at a high round count Hk416's...

keep in mind for every action there is an equal and opposite reaction –– any bolt carrier tilt will wear on both upper and the BOLT

As well as much as the surface of the upper is annodized the soft aluminum is underneath and can be crushed/dented by the bolt 'bouncing' down the upper –– not visible until many many rounds but food for thought.

Posted: 3/19/2009 12:58:57 PM EDT

[#48]

He said the Norwegian special forces still use a DI AR-15 (C8 made by Colt Canada) and they are not having the same issues, so yes, it is a piston problem.

ahem.... BS. there are more diffrences between the 416 and the M4 than simply the piston. hell, just about the entire upper of a 416 is different from the M4, even the parts unrelated the gas system. The bolt is different for one. Ever think the differences in the bolt could lead to icing problems? The firing pin mechanism is very different as well. And why would the piston prevent the charging handle from working.

To re-cap, you have no technical argument, your argument is that our Norwegian friend Tanfo is a liar. Does that about sum it up?

Try again Spiff. I'll discuss the technicalities with you. There is no way to know WHAT the cause of the problem was from those limited posts.

And I didn't call Tanfo a liar, but I have dealt with "troop scuttlebutt" enough to know that sometimes the tale grows in the telling.

Posted: 3/19/2009 1:34:28 PM EDT

[#49]

Quoted:

He said the Norwegian special forces still use a DI AR-15 (C8 made by Colt Canada) and they are not having the same issues, so yes, it is a piston problem.

ahem.... BS. there are more diffrences between the 416 and the M4 than simply the piston. hell, just about the entire upper of a 416 is different from the M4, even the parts unrelated the gas system. The bolt is different for one. Ever think the differences in the bolt could lead to icing problems? The firing pin mechanism is very different as well. And why would the piston prevent the charging handle from working.

To re-cap, you have no technical argument, your argument is that our Norwegian friend Tanfo is a liar. Does that about sum it up?

Try again Spiff. I'll discuss the technicalities with you. There is no way to know WHAT the cause of the problem was from those limited posts.

And I didn't call Tanfo a liar, but I have dealt with "troop scuttlebutt" enough to know that sometimes the tale grows in the telling.

Troop scuttlebutt would be that the "M4 jams all the time and pistons are the best". Tanfo's post was more of a field report. You don't have the technical background to discuss mechanical design in any real detail with me, no offense. I have nothing further to add, this conversation has run its course.

Posted: 3/19/2009 1:45:56 PM EDT

[#50]

Quoted:

He said the Norwegian special forces still use a DI AR-15 (C8 made by Colt Canada) and they are not having the same issues, so yes, it is a piston problem.

ahem.... BS. there are more diffrences between the 416 and the M4 than simply the piston. hell, just about the entire upper of a 416 is different from the M4, even the parts unrelated the gas system. The bolt is different for one. Ever think the differences in the bolt could lead to icing problems? The firing pin mechanism is very different as well. And why would the piston prevent the charging handle from working.

To re-cap, you have no technical argument, your argument is that our Norwegian friend Tanfo is a liar. Does that about sum it up?

Try again Spiff. I'll discuss the technicalities with you. There is no way to know WHAT the cause of the problem was from those limited posts.

And I didn't call Tanfo a liar, but I have dealt with "troop scuttlebutt" enough to know that sometimes the tale grows in the telling.

Troop scuttlebutt would be that the "M4 jams all the time and pistons are the best". Tanfo's post was more of a field report.

Agreed. but hardly definitive.

You don't have the technical background to discuss mechanical design in any real detail with me, no offense. I have nothing further to add, this conversation has run its course.

Think again. be careful about throwing your "technical expertise" around. I have a degree in mechanical engineering and have been working as an R&D engineer in the defense industry for about 20 years. The information posted by Tanfo was insuffiecient to determine the cause of the stoppages. If you came to any CCB I ran and wanted to submit your "analysis" as a technical analysis in repsonse to a trouble report, you'd be laughed out of the room Mr. Technical Expert.

For the last time. I take no position on whether pistons are superior to DI or the opposite. I'm saying THAT doesn't constitute definitive proof of anything in particular other than there's a problem of unknown origin with the weapon.

[ARCHIVED THREAD] - Why do Piston BCGs tilt and DIs don't? (Page 1 of 2)

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