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1/22/2020 12:12:56 PM
Posted: 9/9/2007 6:51:48 PM EST
[Last Edit: 10/11/2007 5:54:58 PM EST by 11B30B4]
Updated 10/11/07

In September of 2006 I was reading my copy of Small Arm’s Review and loved the article about the Colt Defense’s rifle submissions for the SCAR (Special Operations Forces Combat Assault Rifle). Colt submitted three types of rifles, both type A and B were traditional gas impingement systems and type C was a gas piston system.










So I decided to build my own SCAR type B rifle as closely to the original specs as cost would allow. In this process I ended up with this:




After my type B I knew I would eventually go to a gas piston. I was impressed with the Colt Type C (what eventually developed into the LE 1020) and the HK 416. I chose the POF over LWRC for a number of reasons. I feel that the weapons and the systems are for the most part evenly matched. However, the POF does not incorporate a spring in the gas piston system and I like the POF lower better. So I am currently building this rifle and will post pics when finished.
UPDATE: The POF project is almost complete. Here it is so Far...








I chose a Semi-gloss Flat Dark Earth this time over the Flat paint. It seems the Semi-gloss gets into the small areas better and it is a closer match to the Voltr Flat Dark Earth. You may also notice that the "Tuff Coat" that AAC used on my M4-1000 silencer has not delt with the heat very well. I am curently exploring other options "ceramic" and will keep you all informed.

Several months ago I started a thread asking who makes gas piston AR’s and only a few manufactures were listed in response. Someone asked me to get a list together so here is what I have so far. If anything seems incorrect or you can provide additional information please reply or send me a PM.

A lot of people have been asking which is best or what the difference is so I hope this clears up some questions.

As far as I know, the first gas piston AR type assault rifle was the Colt Model 703 made in the late 1960’s. Seen here:




Colt decided to never develop the rifle because the issues with the M-16 were address and the design was adopted by the military.

Today there are many manufacturers of the gas piston AR type rifle. As far as I can tell, there are two schools of thought for the gas piston system. Both systems do basically the same thing only slightly different. A short stroke tappet where a two piece piston/ operating rod strike the face of the bold carrier group driving it rearward and the piston rod returns to its forward potion by a spring. Most manufacturers use a three piece system. The piston, operating rod, and spring found in the Colt, HK, Kurt’s Kustom, and LWRC. The other system uses only two moving parts. A piston and a operating rod and the system resets by the force of the already present recoil spring and buffer found in the Ares and POF/ Bushmaster. Each manufacturer has there spin on how long the parts are, what they are made of, and how they are attached and removed. So I have complied some basic data and pictures of the various manufacturers.

Kurt's Kustom Firearms, LLC
http://www.kurtskustomfirearms.citymax.com/page/page/8932.htm
This KKF exclusive gas system (pat. pending) for the M16/AR15 family increases reliability, runs MUCH cleaner through the use of an op-rod system, bleeding no barrel gasses back into the action, and runs smoother. Easy operator takedown if maintenance is ever necessary. Components are machined from stainless steel and titanium. The Carbine and mid-length system assemblies and tuned uppers will be available 01/2007. KKF can upgrade your existing system to the KKF M9Evo for the special introductory price of $395. Complete uppers: 14.5" M4-$895 (prices subject to change without notice).










LWRC
http://www.lwrifles.com/
The short stroke piston system employing a "cup over nozzle" short stroke arrangement limits the reciprocating weight of the piston system and thus prevents disturbing the barrel harmonics and accuracy. With reciprocation of the piston cup, carbon is scraped away from the internal walls of the cup by the fixed ribbed nozzle and blown harmlessly out of the vent holes with the next cartridge fired. This makes the piston system almost maintenance free. Complete uppers for about $ 1500.00. They have also been known to upgrade your upper if you send it to them.












POF/ Bushmaster/DS Arms
http://www.pof-usa.com/
http://www.bushmaster.com/catalog_parts_upper_receivers.asp#BURA3B16M4GP
http://www.dsarms.com/searchprods.asp
P.O.F-USA has engineered, manufactured and tested this system. We are extremely proud of the durability and performance of the P-415 / P-416 Gas-Piston uppers. We have eliminated features of the Gas Operating System such as gas-rings, gas tube, and gas key. The P-415 / P-416 Gas-Piston system also eliminates Heat, Carbon build up and Gas Leaks which can have an adverse effect on the operating system. The biggest issue being "HEAT". A weapons first priority, must be "RELIABILITY". We first displayed our gas piston uppers at the 2004 Shot Show. We have engineered the entire system using standard "AR15/M16" style parts such as the flat top receiver and bolt. We add only three additional parts to operate our gas piston uppers (Gas plug, Gas piston, and push rod). All uppers come standard with C.R.O.S ™ (Corrosion Resistant Operating System), which allows our weapon system to operate without the need of lubricant. Complete uppers for about $ 1100.00










Ares Defense
http://www.aresdefense.com/product.html
GSR-35 Black Lightning™
The GSR-35 Black Lightning™ (Gas System Retrofit) is a Patents-Pending, short-stroke piston conversion for M16-type battle carbines. The GSR-35™ replaces the standard and often problematic direct-gas system with a lightweight operating rod and low-maintenance piston. Once installed, there are no more broken gas rings, droopy gas tubes or hot gases vented into your weapon. Instead, the GSR-35™ vents the gases under the hand guard and away from the operator. The high-performance bolt carrier features increased mass, an integral impact lug and specially designed anti-wear features to protect your receiver. Unlike competing products, the GSR-35 Black Lightning™ is readily installed into your factory upper receiver assembly without permanent modification to your carbine. You keep your factory receivers, barrel and bolt. It utilizes standard hand guards which are supplied with the kit, and a MIL-STD-1913 Rail Interface hand guard is under development. The result is a cleaner and more reliable system that is sure to enhance the overall performance and reliability of your weapon. The GSR-35 Black Lightning™ is in production and available for both semi-automatic and full-automatic weapons. Sells for about $ 399.00 they have two systems, one for 10.5- 14.5 inch barrels and one for 14.5- 16 inch barrels. This is a do it yourself kit and there has been a lot of controversy about the reliability of this system. This may be based on the skill of the installer rather than the system its self.






Colt
The Colt LE 1020 has its history in the Colt 703 which was revised in 2005 for the SCAR type C submission rifle. I have no idea how much they cost and I have found very little information about them. A good resource is Small Arms Review Volume 10, Number 10, July 2007.










H&K
http://www.hk-usa.com/le_hk416_general.html
The HK-proprietary gas system does not introduce propellant gases and the associated carbon fouling back into the weapon’s interior. This reduces operator cleaning time, increases the reliability of the weapon and extends the interval between stoppages. I have no idea what they cost.




Lewis Machine and Tool (LMT)
http://www.lewismachine.net/
Article from Defense Review: http://www.defensereview.com/modules.php?name=News&file=print&sid=973
DefenseReview got to fire a Lewis Machine & Tool (LMT) gas-piston/op-rod-driven MRP (Monolithic Rail Platform) tactical carbine (AR-15/M16 configuration) while we were at the Knight's Armament Company (KAC) shoot (at their outdoor ranges behind their manufacturing facility). We did not experience any malfunctions while we were firing it, nor did we witness any malfunctions while others were doing so. Operation was pretty smooth, and recoil was about what you'd expect with a gas-piston-driven 5.56. It was a joy to shoot, actually. By the way, the beauty of the LMT gas-piston/op-rod system is that it's drop-in/convertible. In other words, you can buy a standard direct-gas-impingement LMT MRP and the gas-piston/op-rod system components, and you've essentially got two rifles in one, the best of both worlds, so to speak. Pretty neat system.

Unfortunately, the Lewis Machine & Tool (LMT) gas-piston/op-rod system is still under development, so you'll have to wait a little while. If I remember correctly, we're looking at sometime between April and June 2007 (unconfirmed/unverified), but don't hold me to that. At the moment, I'm not even sure that LMT will even release it. I'll have to call and check.
UPDATE- Rumor has it, pricing any day now and product availability just in time for Christmas (Nov-Dec), more to come.












Magpul
http://magpul.com/tech/masada.html
The gas system is based on the AR180 design and, like the bolt carrier group is designed to stay together as a unit when removed from the rifle. All parts are easily stripped for cleaning.






ZM Weapons
http://www.zmweapons.com/index.htm
Although it looks like a gas piston gun, I can not find any information that says it is nor are there any pictures of the gas system.
UPDATE
Ok ZM is not a “gas piston” gun nor is it a “direct impingement” gun. I guess you could call it a “gas deferred” gun. From what I see in this new picture (and thank you chibajoe for the picture) the gas comes into a chamber above the gas block and forces a really long operating rod (that is directly attached to the gas key) back and that in turn forces the modified bolt carrier (cut down) back. Then a recoil spring around the op-rod returns it to the chambered position. This system eliminates the need for a buffer, buffer tube and buffer recoil spring. Further it diverts gas from inside the receiver which is the goal of most alternative gas systems.





UPDATE
Well a friend sent me this link and I feel they should be added to this thread. It seems that PWS took some ideas from the AK, ZM and POF and rolled them into one concept. And it will be available just in time for Christmas

Primary Weapons Systems
http://www.primaryweapons.com/store/pc/home.asp
Having dealt greatly with the reliable yet substandard ergonomics of the AK47, PWS wanted to bring the reliability of the AK to the familiar ergonomics of the AR15 platform. This in house retro-fit is installed on the customer's upper at the PWS facility or as a new build option at our certified dealers only.
Installation
This retro-fit system is installed by fitting our modified carrier key and anti-shear pin on the customer's existing bolt carrier and the operating rod is pressure fit into our carrier key. The gas block assembly is installed and pinned in place.
Note: we have found that opening the gas port in the barrel approximately .010" leads to better overall function of the weapon system. This is done by using a set of 3 reamers that are progressively larger to maintain the integrity of chrome lined barrels.
Function
When the rifle is fired, the developing gases expand inside of the gas block much like a traditional DI system. The expanding gases push against our short stroke piston which exerts pressure on the operating rod and thus gives momentum to the bolt carrier. Once the piston itself has traveled 3/4", it expels any unused gas from a small vent in the bottom of the piston tube. As the cycle of the action is already in progress, the piston moves to the back of its chamber awaiting the return of the operating rod to push it back into battery.
The web site says they will be available in Dec 2007 selling at $399.99.
















Barrett
http://www.barrettrifles.com/rifle_468.aspx
Not a gas piston gun, but rumor has it, they are developing one

XCR (Robinson Arms)
http://www.robarm.com/index.htm
Not really an AR-15 design but a nice gun never the less

FN Herstal
http://www.fnherstal.com/
Yet again, not an AR

Sig Arms
http://www.sigarms.com/Products/ShowCatalogProductDetails.aspx?categoryid=35&productid=114
Ditto, not an AR

Well that’s what I have so far. I look forward to your comments.

Link Posted: 9/9/2007 7:15:20 PM EST
wow! Lots of info. Thanks!
Link Posted: 9/9/2007 7:17:18 PM EST
Request to sticky this highly detailed thread.
Link Posted: 9/9/2007 8:30:48 PM EST
good stuff. thanks
Link Posted: 9/10/2007 11:11:09 AM EST
[Last Edit: 9/10/2007 11:11:48 AM EST by DevL]
You should at least show the carrier of the LWRC system and the proprietary gas blocks used on the A2 versions to compare to the others IMO.

I dont think that a buch of AR180 and AK based weapon actions belong in a thread about piston ARs IMO. Might as well throw custom AKs with AR stocks on the list.

ZM Weapons is a DI system, not a piston.
Link Posted: 9/10/2007 11:25:07 AM EST
Nice posting with some good pics and info.

Here's so more for the thread,

Piston AR pic thread
Link Posted: 9/10/2007 11:35:46 AM EST
What about the LMT MRP retrofit coming soon?

Great post!
Link Posted: 9/10/2007 12:00:57 PM EST
Link Posted: 9/10/2007 12:36:46 PM EST
Awesome post man, thanks!
Link Posted: 9/10/2007 1:00:49 PM EST
Excellent post, very nice to see pics and info on all the systems at once- definitely deserves a tack.
Link Posted: 9/10/2007 2:04:35 PM EST
Thanks for your effort!

Well done.
Link Posted: 9/11/2007 4:27:15 AM EST
DevL,
I thank you for your comments. As for the pictures of the LWRC, I do not own one to photo and I could not put every picture I found on the web in this thread. However, if you feel that the gas block or another component that sets it apart from the other manufacturers. Please send me an e-mail or pm and include the photos you feel should appear.
As for the inclusion of the Magpul, Robinson Arms, FN, Sig, and Barrett, I was simply attempting to state up front that they were not AR weapons. I hoped this would prevent them from entering discussion later in the thread.
As for the ZM, I think it is DI as well but I still can not confirm it. If anyone has any pictures that clearly show the gas system and that the weapon in the picture is in fact a ZM, I would appreciate them.

MisterWilson,
Per your request, LMT has been added, if anyone has pictures please send them to me.

Thank you everyone for your comments
Link Posted: 9/11/2007 5:42:28 AM EST
Great info... good post.
Link Posted: 9/11/2007 8:08:50 PM EST
You might want to add the Barrett piston upper.
Link Posted: 9/11/2007 11:30:59 PM EST
Looks like the selector switches don't have to rotate a full 90 degrees to get to one mode. Good idea!
Link Posted: 9/12/2007 3:49:09 AM EST
Link Posted: 9/12/2007 4:49:38 AM EST
[Last Edit: 9/12/2007 4:53:19 AM EST by DevL]
ZM Weapons has a longer key and a shorter gas tube. The key goes under the handguards and the gas tube is very short. The recoil spring is located above the moving parts instead fo behind them. There are no pistons, short stroke or otherwise.



LWRC carrier with eletroless nickle / teflon coating (same coating as NP3)

I will get a pic of the gas block.
Link Posted: 9/12/2007 5:18:34 AM EST
ZM is an impingement system with the gas key extending to the gas block. The return spring is forward of the upper receiver, under the handguards. The carrier is a standard one shortened so that when fully retracted (at the end of its stroke) it does not protrude beyond the upper receiver. The gas key is taller than standard keys. As a result, the gas tube hole in the upper receiver is located higher. I have a ZM carrier in my parts box awaiting its marriage to a DPMS lo-pro upper and modified gas block.

buckmeister
Link Posted: 9/12/2007 7:51:30 AM EST
Nice job! This deserves a sticky!!!!!!
Link Posted: 9/12/2007 9:20:45 AM EST
well done , great info and pics.
Link Posted: 9/12/2007 5:23:03 PM EST
DevL, thanks for the carrier pic. i found some pics of the gas block and added them to the LWRC section.


Originally Posted By Blackjack272:
Looks like the selector switches don't have to rotate a full 90 degrees to get to one mode. Good idea!

Which rifle are you talking about?


Thanks everyone for your comments
Link Posted: 9/13/2007 7:12:13 AM EST
Excellent compilation!
Link Posted: 9/13/2007 9:44:30 AM EST

Originally Posted By 11B30B4:
DevL, thanks for the carrier pic. i found some pics of the gas block and added them to the LWRC section.


Originally Posted By Blackjack272:
Looks like the selector switches don't have to rotate a full 90 degrees to get to one mode. Good idea!

Which rifle are you talking about?


Thanks everyone for your comments


Take a close look at the SCAR Colt submissions.
Link Posted: 9/13/2007 9:58:43 AM EST
Awesome post...I am going piston next build. Screw crapping in my own backyard for now on
Link Posted: 9/13/2007 12:36:06 PM EST
An interesting question that has arisen is whether the bolt carrier scrapes the buffer tube in recoil due to the off axis force impartd by the op rod striking the carrier key.

I have noticed a little scraping in my buffer tube.

Someone posted a picture in another thread that had excessive scraping.

I was told that LW & HK use carriers that are fatter at teh back end to preclude any potential alignment problems.
Link Posted: 9/14/2007 9:01:28 AM EST
Did anybody else notice the thread on LWRC’s company owned forum asking if they were having financial problems? The original poster stated they were actually laying off employees. I was watching the thread closely for an official response from the company but instead the thread was trashed very quickly. Nobody has mentioned it sense but that’s not surprising considering it’s a company owned forum so they can do what ever they want. I’m sitting on the fence for a new upper and had been considering them but I don’t want to get stuck buying a product from a company that might be going under.

Does anybody know LWRC current condition? Are they really laying off employees? If so, what does that mean? Will customers be able to still get parts for their guns?

- I’m glad I finally registered for an account. I have been reading the forum for almost a year.


Link Posted: 9/14/2007 6:17:41 PM EST

Originally Posted By SC-Texas:
An interesting question that has arisen is whether the bolt carrier scrapes the buffer tube in recoil due to the off axis force impartd by the op rod striking the carrier key.

I have noticed a little scraping in my buffer tube.

Someone posted a picture in another thread that had excessive scraping.

I was told that LW & HK use carriers that are fatter at teh back end to preclude any potential alignment problems.

I have seen that thread as well. I do not know if it is an isolated incident or a problem indicative of the pas piston.
Common sense would dictate that the various manufacturers would have considered this in the design and alter the specs of the carrier to compensate. It’s probably one reason that each system comes complete with a proprietary carrier (in addition to the key design).

I fired 20 mags through my POF today and did not observe any wear in the tube.

I do know that Colt added skies to the bottom rear of its carrier in the 703 project and expanded on it in the SCAR and LE1020. It looks like the LMT thickened the rear of its carrier. When I get some time in the next week I will post some pictures of the different carriers.
Link Posted: 9/14/2007 6:23:58 PM EST

Originally Posted By Wikingfan:
Did anybody else notice the thread on LWRC’s company owned forum asking if they were having financial problems? The original poster stated they were actually laying off employees. I was watching the thread closely for an official response from the company but instead the thread was trashed very quickly. Nobody has mentioned it sense but that’s not surprising considering it’s a company owned forum so they can do what ever they want. I’m sitting on the fence for a new upper and had been considering them but I don’t want to get stuck buying a product from a company that might be going under.

Does anybody know LWRC current condition? Are they really laying off employees? If so, what does that mean? Will customers be able to still get parts for their guns?

- I’m glad I finally registered for an account. I have been reading the forum for almost a year.



Thanks for your input but I would not want to speculate on something I do not know. What I do know is that the wait time (I called last week) for an upper is 17 weeks, that’s about the same as POF’s wait time. So I guess we will have to wait and see if anything comes out officially.
Link Posted: 9/14/2007 8:19:24 PM EST

Originally Posted By 11B30B4:

Originally Posted By Wikingfan:
Did anybody else notice the thread on LWRC’s company owned forum asking if they were having financial problems? The original poster stated they were actually laying off employees. I was watching the thread closely for an official response from the company but instead the thread was trashed very quickly. Nobody has mentioned it sense but that’s not surprising considering it’s a company owned forum so they can do what ever they want. I’m sitting on the fence for a new upper and had been considering them but I don’t want to get stuck buying a product from a company that might be going under.

Does anybody know LWRC current condition? Are they really laying off employees? If so, what does that mean? Will customers be able to still get parts for their guns?

- I’m glad I finally registered for an account. I have been reading the forum for almost a year.



Thanks for your input but I would not want to speculate on something I do not know. What I do know is that the wait time (I called last week) for an upper is 17 weeks, that’s about the same as POF’s wait time. So I guess we will have to wait and see if anything comes out officially.


To clear the air.... No we are not having financial problems. Yes we did dismiss 3 employees. The reason for their dismissal is between us and our former employees.

The reason the thread was thrashed on our forum was because of whom started it.

Prior to our operators course, we had a number of people (some ar15.com members)through our shop. I'm pretty sure they will attest to our stability and growth.

See you guys at "Modern Day Marine" and "Shot Show 08"
Link Posted: 9/15/2007 1:08:04 PM EST

Originally Posted By LWRC_Jesse:

Originally Posted By 11B30B4:

Originally Posted By Wikingfan:
Did anybody else notice the thread on LWRC’s company owned forum asking if they were having financial problems? The original poster stated they were actually laying off employees. I was watching the thread closely for an official response from the company but instead the thread was trashed very quickly. Nobody has mentioned it sense but that’s not surprising considering it’s a company owned forum so they can do what ever they want. I’m sitting on the fence for a new upper and had been considering them but I don’t want to get stuck buying a product from a company that might be going under.

Does anybody know LWRC current condition? Are they really laying off employees? If so, what does that mean? Will customers be able to still get parts for their guns?

- I’m glad I finally registered for an account. I have been reading the forum for almost a year.



Thanks for your input but I would not want to speculate on something I do not know. What I do know is that the wait time (I called last week) for an upper is 17 weeks, that’s about the same as POF’s wait time. So I guess we will have to wait and see if anything comes out officially.


To clear the air.... No we are not having financial problems. Yes we did dismiss 3 employees. The reason for their dismissal is between us and our former employees.

The reason the thread was thrashed on our forum was because of whom started it.

Prior to our operators course, we had a number of people (some ar15.com members)through our shop. I'm pretty sure they will attest to our stability and growth.

See you guys at "Modern Day Marine" and "Shot Show 08"


Interesting - I'd heard things were tight there but didn't know they'd let people go.
Link Posted: 9/15/2007 6:23:20 PM EST
Thanks Jesse, I think that should clear up the LWRC question.

So has anyone seen or heard anything about the Barrett Gas Piston?
I am still looking for information.
Link Posted: 9/16/2007 12:26:38 PM EST
Is there a thread that discusses the bolt carrier scraping the buffer tube?
Link Posted: 9/20/2007 1:34:26 PM EST
[Last Edit: 9/21/2007 4:51:12 AM EST by 11B30B4]
Ok guys here is the latest from me. My intention is not to slam POF. This post is to hopefully help anyone experiencing carrier scraping in the buffer tube. I would think that this phenomenon could exist in almost any gas piston AR. However, I happen to own a POF so most of my comments will be based on my experience with it.

That Said, I have tried to contact POF everyday this week. I left a message for them to call me back on Monday and never heard from them. Every time I have called this week I get their voicemail. I wanted to wait until I had the opportunity to talk with them but since they are not answering the phone and since they have not called me back. I have given them the opportunity to address this issue in a reasonable time frame. So I have attempted to fix my issue myself and here is the story.

I have had my 11.5” .226 POF upper for a few weeks and have delayed shooting it because I planned on getting it painted FDE along with my newly engraved (SBR) POF lower. But after seeing the POF Kaboom post, I figured I would put it on my Bushmaster lower and pump some round through it to make sure everything was good to go.
I should note that the butt stock on my bushmaster is a Choate M-4 (SOCOM) style mil spec stock with a “H” buffer.
So I head to the range and pump 5 rounds through the POF and stovepipe #1 happens. I clear the weapon and the only thing I could figure is that the piston is set for suppressor. So I flip it around and pump two mags with no issues. Then I flip the piston again and put on my AAC M4-1000 suppressor.
I fire off three rounds and stovepipe #2. I check everything and find nothing wrong so I shoot two more mags then stovepipe #3. Again I check everything and decide that it just needs to be cleaned. The suppressor kicks a lot of carbon back into the upper, even on piston guns.
So I go home and let the gun sit for two days then I get a message asking about buffer strikes. So I start thinking maybe that’s what’s happening with my POF. So I go to clean and inspect my POF and I discover that the bolt carrier has ripped out the buffer retention pin. I find the spring in the lower receiver next to the trigger group. And there is considerable damage to the face of the buffer tube.






I decide to remove the buffer tube and cut about ¼” off the threaded end and refinish it to fit like factory. The Choate tube has a cut out for the buffer retention pin, but I decided to simply have the tube screw in and stop at the desired spot to hold in the buffer retention pin like in a Vltor tube. I ended up having to shave the bottom side of the tube about 1/32” in the threads to allow the buffer retention pin to seat properly. I figure the tube being ¼” shorter in total length would not be a big issue.




So today I go and pump several mags suppressed and unsuppressed with no issues.
As best as I can tell, my issue was that the buffer retention pin was protruding just enough to allow the bolt carrier to strike it causing the damage and stovepipe issues. I think my fix has worked and I will only be sure after a lot more rounds. I will keep you informed on any further developments.

Special thanks to DAC for the help with gunsmithing
Link Posted: 9/20/2007 1:44:40 PM EST
The clinical explanation of buffer tube scraping.
The issue you are dealing with is called carrier tilt. In a standard DI the bolt/carrier work in-line with the bore axis. This changes with an over-head/over the bore piston set-up. Because the op rod in now acting/pushing against the carrier off bore-axis the carrier nose/front will want to lift upward and the ass end will want to tilt downward. We call this carrier tilt or carrier rise. This is what's causing the wear you described.

To remedy this problem some manufacturers use simple engineering. First they incorporate a downward slant in the carrier key. If you notice some manufacturers are using a small tomb-stone like striking face on their carriers. This is the root cause of the issue, the linear force being applied off bore-axis. Some manufacturers on the other hand, use a solid key which is dove-tailed into the carrier. This method allows four key benefits
1) Allows them to moves the impact point as far forward as possible
2) Allows then to incorporate the downward slope
3) Allows them to use a material which is designed for high impact loads
5) Allows them to use a shorter and smaller O.D. op rod
4) Allows replacement if needed

By moving the point in which the carrier is struck by the op rod as far forward as possible and incorporating the slanted key geometry some manufacturers are able to revector the linear force back to almost bore center-line.

The second change to the DI carrier design, some manufacturers engineered a boss onto the end of our carrier. By adding this boss any last bit of carrier tilt in their system is removed, because the tail end is now supported by the buffer tube.

LWRC uses this remedy.
Link Posted: 9/20/2007 3:53:32 PM EST

Originally Posted By 11B30B4:
The clinical explanation of buffer tube scraping.
The issue you are dealing with is called carrier tilt. In a standard DI the bolt/carrier work in-line with the bore axis. This changes with an over-head/over the bore piston set-up. Because the op rod in now acting/pushing against the carrier off bore-axis the carrier nose/front will want to lift upward and the ass end will want to tilt downward. We call this carrier tilt or carrier rise. This is what's causing the wear you described.

To remedy this problem some manufacturers use simple engineering. First they incorporate a downward slant in the carrier key. If you notice some manufacturers are using a small tomb-stone like striking face on their carriers. This is the root cause of the issue, the linear force being applied off bore-axis. Some manufacturers on the other hand, use a solid key which is dove-tailed into the carrier. This method allows four key benefits
1) Allows them to moves the impact point as far forward as possible
2) Allows then to incorporate the downward slope
3) Allows them to use a material which is designed for high impact loads
5) Allows them to use a shorter and smaller O.D. op rod
4) Allows replacement if needed

By moving the point in which the carrier is struck by the op rod as far forward as possible and incorporating the slanted key geometry some manufacturers are able to revector the linear force back to almost bore center-line.

The second change to the DI carrier design, some manufacturers engineered a boss onto the end of our carrier. By adding this boss any last bit of carrier tilt in their system is removed, because the tail end is now supported by the buffer tube.

LWRC uses this remedy.

Very well explained. Every bit of it makes sense.
I like the remedy of adding a little meat to the backend of the carrier. I think that this will resolve anymore tilting of the bolt carrier issues.
Of course both of my POFs are fine. Barely any scraping at all in the buffer tube. One of the carriers have the made on carrier key and the other has the bolted on and pinned one.
Link Posted: 10/5/2007 5:56:50 PM EST
[Last Edit: 10/5/2007 6:40:23 PM EST by 11B30B4]
Added some pics, also I talked to LMT. looks like the LMT piston will be priced in the next few weeks and orders will be shipping in Jan.







Link Posted: 10/5/2007 6:32:52 PM EST
[Last Edit: 10/5/2007 6:36:55 PM EST by Achilles1]
Maybe this is just me, but if your getting wear on your buffer tube from the carrier than grease that puppy up and keep it greased (or oiled) to prevent and lower that wear. That goes for the buffer tube in deeper, and the buffer and spring too.
This isn't a DI. There isn't a mass of carbon flowing into the receiver that a person should worry about gum-up the same from using grease.
That doesn't mean whip out the 1920's axle grease your Grandaddy had stored forever in the basement and was now passed down to you.
I like Tetra grease, but there are certainly other good modern gun grease choices out there like XF-7 or Militec.
I see more wear from people not lubricating properly or sufficiently than not.
Link Posted: 10/5/2007 6:39:04 PM EST
Achilles, thanks for the suggestions. I have considered using grease in the buffer tube. I do use Militec on the working parts. I will look into a lithium based grease for the buffer tube.
Link Posted: 10/5/2007 6:41:59 PM EST

Originally Posted By 11B30B4:
Added some pics, also I talked to LMT. looks like the LMT piston will be priced in the next few weeks and orders will be shipping in Jan.

i12.photobucket.com/albums/a208/11B30B4/ORight.jpg

i12.photobucket.com/albums/a208/11B30B4/OLeft.jpg

i12.photobucket.com/albums/a208/11B30B4/Right.jpg

i12.photobucket.com/albums/a208/11B30B4/Left.jpg


That's a sweet looking POF setup.
Link Posted: 10/5/2007 7:19:42 PM EST
[Last Edit: 10/5/2007 9:27:48 PM EST by chibajoe]

Originally Posted By DevL:
ZM Weapons has a longer key and a shorter gas tube. The key goes under the handguards and the gas tube is very short. The recoil spring is located above the moving parts instead fo behind them. There are no pistons, short stroke or otherwise.

i178.photobucket.com/albums/w247/LWRC_Jesse/JesseBC.jpg

LWRC carrier with eletroless nickle / teflon coating (same coating as NP3)

I will get a pic of the gas block.


Here is a picture of the gas system from the ZM Weapons AR:



ETA The abreviated carrier allows the buffer tube to be eliminated and replaced with a folding stock, but (as far as I can tell) would not work with a FA lower or a RDIAS. While it's not a gas piston, it does solve the problem of keeping the carbon out of the interior of the gun, and I haven't had any problems with it.
Link Posted: 10/5/2007 7:32:56 PM EST
Very interesting thread comparing the different gas piston systems.

Thank you for the informative post.
Link Posted: 10/11/2007 2:20:24 PM EST
Any resolution on the buffer scraping?
Link Posted: 10/12/2007 5:10:25 AM EST
[Last Edit: 10/12/2007 5:10:51 AM EST by ABNAK]
I have a LWRC M6A2 upper and it too has some wear on the bottom of the buffer tube. However, it is more of a smooth, beveled wear (if there is such a thing) as opposed to gouges like were shown in the pics of the POF. It hasn't affected function so far. I just hope it's the kind of thing that only wears so far then is good to go and not the kind that will continue to dig down indefinitely.


ETA---my LWRC upper is on a Bushy lower so the buffer tube is not of LWRC design (if indeed their's is any different to accomodate this issue).
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