Let me start out by saying that I am an DGI disciple––I do not think that a gas piston makes the rifle any more reliable than it already is since 99.99% of malfunctions are tied to the magazines and extractor––something a gas piston conversion does not affect at all. Despite my  opinion, $250 was too small of a price to pay to play with a piston. Actually, $250 is a misnomer as I purchased a new carrier for this project. The real price is around $310 or so after taxes.

Okay, so I finally received my gas piston kit today. I installed it in one of my M4's.

Initial impressions:

The instructions are terrible. The images are too small and the directions not specific enough. Since this conversion requires a gas key replacement I purchased a stripped bolt carrier instead of mucking up one of my LMT carriers.

http://img.photobucket.com/albums/v11/DavePAL84/projects/GP7.jpg

First, I completely stripped the rifle (pulled off the quad rail and took the optics off)
http://img.photobucket.com/albums/v11/DavePAL84/projects/GP4.jpg

I knocked out the roll pin for the gas tube and pulled out the gas tube. Since this rifle hasn't been shot a whole lot it came out easily
http://img.photobucket.com/albums/v11/DavePAL84/projects/GP2.jpg

I field stripped the old bolt carrier and removed the gas rings
http://img.photobucket.com/albums/v11/DavePAL84/projects/GP10.jpg

Then I installed the new gas key onto the stripped carrier and staked it into place. The front screw is longer than the usual front screw for some reason.

I replaced the gas tube with a short tube and roll pin (new, longer pin was included)
http://img.photobucket.com/albums/v11/DavePAL84/projects/GP3.jpg

Assembled piston and spring
http://img.photobucket.com/albums/v11/DavePAL84/projects/GP1.jpg

Here is a pic of the new cylinder block assembly
http://img.photobucket.com/albums/v11/DavePAL84/projects/GP8.jpg
The cylinder block fits onto the gas tube and the piston fits into the rear end of the cylinder block.

Since the barrel is an M4 profile, I had to use the included shims. Unfortunately, the shims were too large. I had to spend some time with a dremel tool before I got them to fit. I'd like the parts to be too large rather than too small but this was more work than I expected. Since the gas block itself was not replaced (which would keep cost down) I think that shims were necessary.

After some dremel work, here is the whole thing together
http://img.photobucket.com/albums/v11/DavePAL84/projects/GP9.jpg

I checked for fit with the quad rail––no go, I had to use the handguards that came with the conversion
http://img.photobucket.com/albums/v11/DavePAL84/projects/GP5.jpg

Because I was unable to use my quad rail, the EOtech had to be moved back so I could not longer have the EOtech, magnifier, and BUIS on the rifle at the sane time. I opted to remove the rear BUIS to keep the magnifier. All together:
http://img.photobucket.com/albums/v11/DavePAL84/projects/GP0.jpg

I'm taking it to the range either tomorrow or Friday. There is no regulator on the piston so I am concerned that Wolf will not cycle––only a test will tell.

If everything goes well with the test, I'll completely clean the rifle and document the wear over the course of 1k rounds without cleaning to see what kind of damage carrier tilt causes (if any). Very few rounds have been fired through the test rifle so any additional unusual wear will be easy to see.

I hope to see a report on this kit soon I have been in a self debate on one of these for a while. I am sure that I am not the only one. great start to what will i hope become a great review as others add more to it.

I'm of the opinion that piston is the answer to jamming problems. Is that system a long piston action? I would be very interested in your evalutaion of how it affects how the gun handles and accuracy vs DGI setup.

Just got back from the range earlier today. I fired Wolf and some M193 through it. I fired a little over 250 rounds. No problems. Handguards got pretty hot have a couple of mag dumps (I wish I had a vert grip on this thing). Accuracy was fine, saw no real difference (it is a carbine afterall). I'm going to strip it all down and clean it to begin the 1k test tonight.

Any unusual marks or wear  in the receiver extension or upper?

Sucks that you can't use your quad-rail anymore.

Is this an issue with all gas piston kits, or just this kit?  That alone would be a dealbreaker for me, as my quad rail holds my VFG and surefire g2l+offset mount.

Some piston conversions will work with quad rails, however most will require you to mod the rail....usually by dremmeling out the underside of the rail system.

ETA- depending on the rail system.

Tag.

Keep this thread updated. I would like to know how it works out after 2000-3000 rounds. I like the way the kit is made to install without permanet modifications to the gun. The spring looks like a weak link and I'm not sure about the gas cylinder clamped to the barrel.

Supposedly, the main advantage to this particular piston system is that it has an expansion chamber, a "gas trap" of sorts, that allows the pressures to drop before extraction takes place. They claim to be able to "tap" the carrier group out of battery as opposed to (all other) piston systems having to knock it out of battery "with a balpeen hammer". This is from a conversation with one of the guys from TNW over the phone and then again at Knob Creek.

I am intrigued by pistons, and have owned/own every one out there but this one, Adams Arms, and ADC's. So I am curious as to whether the "gas trap" theory will work. Even if you don't like pistons, I'd like to hear some PRACTICAL engineering theory on this.

Not a tag

Same type of spring that GLOCK and FN uses. The barrel clamp is a fairly good idea. I doubt the assembly would move without it, unless it met force, just added insurance with the clamp. Bushmaster included one with their modified conversion kit too.

Another 200 rounds through it today. Saw something weird but only happened once. My friend was putting a magazine through and the bolt stayed back to the rear for a split second. Right when I opened my mouth to say, "you have a stoppage" the bolt snapped forward. The rest of the magazine was fine. It was with wolf ammo. There must have been some kind of binding someplace. Never seen that before. I have my suspicions but we'll see what happens when I open her up.

I've noticed that ejection with wolf ammo is not nearly as robust as it is with M193. I haven't cracked her open yet to look at the guts. Will do so and take pictures tomorrow.

It was strange seeing the gas vented from the handguards. It was cold outside today and everytime my friend shot the gas could easily be seen coming from the handguards.

 sounds like carrier tilt or the piston/rod jamming

The problem with piston kits is

CARRIER TILT

I just stripped the gun to do an initial check out. No fouling whatsoever in the upper or lower or on the BCG. I suspected the hangup was from carrier tilt but I see none of the tell-tale signs of wear yet. I'll post pics tomorrow. Something I definitely noticed was the lack of primer sealant all over the place that I usually get from shooting prvi brass.

So I suppose time will tell. 800 more rounds to go with the initial test.


I have been looking into these
http://i162.photobucket.com/albums/t244/seth_100/DSCN1884.jpg

The idea seems solid, I suppose we'll see when they're officially released. I could make a ghetto version in about 10 minutes but I currently don't see a reason to (yet). Of course, the added cost of the new buffer would have to be added to the cost of this system (which hasn't been as inexpensive as they initially appeared). I also wonder what new problems could appear with the re-designed buffer.

To be honest, this piston does not look like a true long stroke piston.  A long stroke piston typically vents nearly towards end of the weapon's stroke (usually more than 1/2 of the way thru).  Short stroke pistons vent early (usually about 1/4th of the way thru) and allow the momentum of the bolt and carrier to complete the stroke.  I could be wrong though - i don't have dimensions to compare...just an eyeball.  But it does appear to be slightly longer than other piston mods.

I'd have to take a closer look at the piston itself to give you some opinions.

But if i had to take a cursory judgement of the piston, if it is indeed a true long stroke piston, then you might get some performance that is a little closer to an AK or m1 garand - where you have a situation of increased reliability at the cost of some precision.  As for an expansion chamber being of less damaging to the carrier, then i'd have to raise a few eyebrows.  The problem of the carrier key getting damaged is the result of a impulse shear force on something that wasn't designed to take a shear force.  Ideally, your carrier should be one that is solid, not screwed on.  In theory, there should be some reduction in wear or damage that is associated with a short stroke piston, because if the gas chamber is larger, there would be a lower starting pressure, and thus a lower impulse.  But in the end, the long stroke piston is moot if all other problems are addressed.

In my honest opinion, i have not seen any piston retrofit to my liking - simply because the ar15/m16 series was not designed to accept it.  In order to make an effective piston, you'd need a situation like the hk416, or masada - where the upper and all parts immediately interacting with the piston is specifically designed to use that system.

So this system dumps all the gas directly into the cavity created by the hand guards?

thanks for the update

It wasn't carrier tilt. Carrier tilt occurs as the recoil process BEGINS, not when it is fully rearward like the OP states. Could it be the rod "jamming"? I guess it's possible, but it sounds like something made it a little sluggish––-a rough spot inside the buffer tube, inside the upper, a burr or something. Maybe even a rough mag.

Carrier tilt wears the extension and can cause sluggish return to battery as the dimensions on the reciever extension change turning it  oval causing alignment problems on return to battery

not a tag

Heh...



You sacrificed your BUIS, railed handguards, and a preferred location for optics just to have a piston?



Yikes.


- BG

I think he did it to TEST a piston.

100% correct.

This is a el-cheapo Del-ton M4 kit I am using as a dedicated T&E gun.

I should mention that I took off the SOCOM stock and put on a beater 6-position instead. I figure if carrier tilt becomes an issue I'd much rather muck up a cheap buffer tube than the $200 SOCOM stock.

The BCG might have snagged on something. Before I put the stock on I noticed some damage on the threaded end of the buffer tube and had to work to fit it (like I said, it was an old beater––no idea what it came off of or when I got it). I have a brand-new 6-pos stock that I'm going to put on because it provides a blank slate to check for unusual wear. I wish I would've thought of that sooner. Oh well

No it doesn't. Given that the front of the tube is encased by the lower receiver (which is where carrier tilt wear occurs––-right at the front bottom by the detent) are you saying that the buffer tube is re-shaped to oval? For that to happen it would also deform the rear of the lower receiver "ring" where the buffer screws in.

I swear, some of you guys read too many piston threads here. CARRIER TILT. OP ROD BINDING OR BREAKING. Yep, must be one of those.

It would have to vent from some where.  Most, if not all, pistons have to vent into the handguards.

Only one I know of doesn't: the HK416. It has a little "exhaust port" on the front of the gas block which blows the excess (unused) gas at an angle upward and forward from the barrel. Gotta say, most piston systems leave a mess *somewhere*, but the HK416 is the easiest to clean BY FAR. I know, I used to own one.

try reading  it's fun duh  mental  the FRONT of the extension wears out usually on one side (Bottom) making it egglike Oval. The resulting condition is bad and can cause problems in the long term.  I don.t just read the threads I have had 3 piston systems to T&E, waiting on the ADams arms so far I like the PWS system, for the way it shoots very smooth.

Uh, you didn't specify in your first post what you clarified in your second. You didn't say the FRONT until the latter post. It initially sounded like you were saying it ovaled the tube itself out, not just the opening. And that delaying bolt carrier return is a new issue to me. I really think the OP's "delay" problem was shitty Wolf ammo and/or a hangup somewhere not piston related.

Oh, and other than the Adams, TNW, and ADC I've had/have every piston system out so far: Ares (x2), HK, LWRC (x2), POF, and PWS. I still have DI guns too so I'm not a "piston snob". How they work intrigues me, and so does trying to answer the questions that their problems pose.

Put around 250 rounds through it today. 150 rounds of Prvi 55gr and ~100 rounds of Wolf (1 bando + some a partial magazine a friend put through it with his ammo).

I noticed before the Wolf made cycling sluggish. This time around I had some FTF's with the Wolf. The BCG moved back far enough to eject the spent casing but it did not move forward with enough force to feed the next round. This happened 2-3 times. Might have been the ammo because I had two bad primers in the 100 rounds of Wolf (dented primer, no firing, not even after feeding it a second time).

I took it home and inspected it. The receiver was still clean (just some red flakes from the red primer sealant from the Prvi ammo) and well lubricated. The part about keeping the upper and lower cleaner is certainly true.

However, the part about carrier tilt is also certainly true. Extensive damage to the bottom of the buffer tube as well as the lower rear of the BCG:

Notice the flakes of metal from the wear:
http://img.photobucket.com/albums/v11/DavePAL84/projects/tilt1.jpg

See how far back the wear is in the buffer tube?
http://img.photobucket.com/albums/v11/DavePAL84/projects/tilt2.jpg

Damage to BCG
http://img.photobucket.com/albums/v11/DavePAL84/projects/tilt3.jpg

Another angle
http://img.photobucket.com/albums/v11/DavePAL84/projects/tilt4.jpg

The front top of the upper receiver (notice how well lubed it still is and the flakes from the primer sealant)
http://img.photobucket.com/albums/v11/DavePAL84/projects/tilt5.jpg

In short: Not worth it, not unless something like this becomes commercially available (and works as well as they say it does)
http://m4carbine.net/showthread.php?t=15453

Also, since it has problems with low-pressure ammunition, if you were going to go with a piston system and want to shoot Wolf I suggest something with a gas regulator.

Good things:
-I replaced my SOCOM stock /w a cheapy 6-pos so I didn't do much damage to a $200 stock.
-Damage to the upper is minimal
-I used a dedicated BCG so no damage done to my good one.
-We now know for certain the TNW system does indeed suffer from carrier tilt.

The binding is probably coming from the whole works not being perfectly aligned with the bore.  It appears it just clamps to the barrel and the only thing keeping it aligned is that short piece of gas tube sticking out of the FSB.

Is this their prototype or what?  It looks very used and unfinished for the most part.  Did it really come in ziploc bags?

ETA:  How are you going to ruin a $200 stock with this thing?  What am I missing?

I contacted TNW yesterday and had a conversation with them about my results. The guy on the phone seemed genuinely surprised and asked if I'd send it in so they could check it out. He said that they don't have that problem, even when running it in an M16 (although the heavier M16 carrier might have something to do with it too). I'm dropping it in the mail tomorrow. Worst case scenario, they can't fix anything. Best case, it comes back running /w no tilt. So far, the customer service seems good (a lot different than calling JAC up for sure  :lol: )

WOW !

Good write up.

I'd like to see that receiver extension and bolt carrier after 5K rounds.

Tag for RR

great write up and very informative.  Thank you very much for this effort, it is most appreciated and the proof of the test cannot be argued.  How come there is no carrier tilt with the Imping system?  There is still strong force pushing into the top of the carrier with the gas system yet.  You'd think that this problem would still exist.  Do you know why this is different?  And, why is this not a problem with the AK system, with the wear just in different places?  Thank you.  

will there be any testing on full auto?

I bought the same system prior to finding this article, needless to say I was apprehensive about the system after reading about it. But still I installed with hopes that it would function properly. So far 500 rounds through action since installation, with absolutely no sign of carrier tilt. I'll be taking it out again this coming weekend, and checking for any signs or wear after every 100 rounds. Hope this helps for any of you that were thinking about running this system.

Tilt does not occur in DI rifles as the gas travels through the key into the carrier where it expands, driving the carrier directly rearward.  The gas pressure isn't pushing rearward against the key on the top of the carrier, it's just traveling through it.

Because the force on the carrier is a product of the pressure and area, that being the OD of the gas tube PLUS the product of the NET area of the carrier ID minus the 0.250" OD of the tail of the bolt.

The mass of the key to the rest of the carrier is proportional to the force of the key compared to the carrier.  

Since acceleration is equal to the product of the force and mass, and the carrier AND the key are accelerating at the same rate, there is minimal load on the carrier screws.  And the carrier/key combination therefore accelerates back in a straight line.

But with pistons, the key receives ALL of the force.  So it wants to move back FASTER than the carrier BUT it is bolted together.  So the carrier must also ROTATE as this is a moment couple.

And don't forget, the carrier screws are taking ALL the load.  In shear.  And that is an engineering faux pas.  BIG TIME.  Unless it is a shoulder bolt AND there is a counterbore for the shoulder to enter and that counterbore is an interference fit....

Far better is the dovetail system, requiring machining and another non-standard part, the dovetailed key, no sense calling it a gas key because it is solid.

All so you can use cheap, turd world ammo in a space-age design.  Do you run cheap Chinese paper in your laser printer?  Run turd world leaded gasoline in your Lexus?  

So, you are adverse to cleaning a rifle.  Get better cleaning tools.  Foaming bore cleaners WORK on more than just bores.  And some others like Pro Shot Copper Solvent IV are cheaper and can be "foamed" by a good shaking in a squeeze bottle.  Apply, let soak, brush and then RINSE WITH WATER.  Yep, dirt is gone but metal is protected from corrosion.  Wipe dry, oil and be done.  If it takes you 20 minutes, you are working slow.

Now, onto the issue you Marys have an issue with...most of that dirt is from the cheap propellents third world countries make.  How is is made?  Cellulose, usually from wood fiber.  Here in the States, we have the best paper plants because we have select pulp trees that have a low lignin level.  And any remaining lignin is removed in the Kraft process, resulting in better paper because lignin prevents the fibers from sticking to each other.  But lignin in the powder?  It does not nitrate like the cellulose so it doesn't burn.  And THAT is most of the dirt in your third world ammo.  Cheap powder.

+1...I love ow manufacturers continue to try and reinvent the wheel.

Things can be improved upon, guys...

If people did not try to improve the wheel you'd still be rolling on stone wheels. Instead, we have steel wheels, forged wheels like Fiske, 3 piece like BBS, cast aluminum ones, and for the ghetto folks... Spinners!

Sooooo..NONE of you guys have "tweaked" a car, truck, mud truck, motorcycle, dirt bike, street bike, snomobile, etc?? All of which "worked fine as designed"? Superior Barrels: How did you get a "longer lasting, more accurate barrel? By taking something that, once again, "worked fine as designed", and tweaking it so it was better? We'd still be shooting cap and ball muskets if it weren't for enterprising guys who thought they could improve on something that "worked fine as designed".

Back to topic:
I have a few concerns involving this review. First let me say that I mean no disrespect to the OP, and I appreciate his effort. Here are my concerns in the order I read them in the OP, along with the information I have accumulated from following this kit from almost the beginning at Weaponeer.

1.Since the barrel is an M4 profile, I had to use the included shims. Unfortunately, the shims were too large. I had to spend some time with a dremel tool before I got them to fit. I'd like the parts to be too large rather than too small but this was more work than I expected. Since the gas block itself was not replaced (which would keep cost down) I think that shims were necessary

The way this kit was originally offered on Weaponeer, you had to select your barrel size when you ordered. Originally there were 3 sizes, now they offer 7. When I talked to Mark at TNW early on about my barrel size (RRA M4 LW - approx .602) He assured me that they would stand behind the kit 100%. The kit in this review was purchaed from Centerfire Systems (as was mine) with no selection of barrel sizes, just a statement that the kit would fit the original 3 sizes, and they have yet to change their description and add the additional sizes. I believe if the OP had contacted TNW about the dremeling issue, they would have assisted him in aquiring the proper shims.

2. In the pic following the above description, I would have to say that it appears to be a sloppy job of installing the shims. Notice how the shim is not in line with the clamping bolt, but behind the area of the clamp, which to me could cause the cylinder block to become misalinged on the barrel. The shim should be directly in line with the clamping bolt. Here is the pic from the OP:


3."This is a el-cheapo Del-ton M4 kit I am using as a dedicated T&E gun. I should mention that I took off the SOCOM stock and put on a beater 6-position instead. Before I put the stock on I noticed some damage on the threaded end of the buffer tube and had to work to fit it (like I said, it was an old beater––no idea what it came off of or when I got it).

How el-cheapo and beater are these parts? How much T&E has this el-cheapo Delton kit seen? Being el cheapo, could the upper be out of spec possibly leading to some of the issues seen here? Is the new carrier purchased an el-cheapo too, if so could it be out of spec, once again possibly helping to produce the issues seen here?

Alot of you guys here bust people balls for buying anything other than Colt, inferring that anything but Colt would or could be out of spec, not Mil-Spec, endanger your life or your health, or cause a catastrophic collapse of the AR world as we know it. But yet in this evaluation we have the use of a dremel to make parts fit, an el-cheapo kit, beater stock with a damaged buffer tube and no one is calling foul on possible sub-standard, out of spec or previously abused parts?

After reveiwing this thread, I e-mailed TNW about this issue. Here is a copy of the reply I received from TNW:
Sir,
We are taking care of the one problem, although we have not had the problem with any of the other
1300 customers. We suspect the problem occurred through a sharp edge on the end of the carrier which
started galling the aluminum. If you or anyone else have a problem with your kit we will take care of it.
  Best Regards
       James McMahon
         TNW Firearms
          503 429 5001
In addition, I called TNW and talked to James just moments ago as I finished up this post. According to James, Mark (I think he is the head honcho) at TNW requested that the OP send in his gun/parts to be evaluated and the problem taken care of. It sounds like as of yet nothing has been sent to TNW for evaluation. After the OP posted this:

"I contacted TNW yesterday and had a conversation with them about my results. The guy on the phone seemed genuinely surprised and asked if I'd send it in so they could check it out. He said that they don't have that problem, even when running it in an M16 (although the heavier M16 carrier might have something to do with it too). I'm dropping it in the mail tomorrow. Worst case scenario, they can't fix anything. Best case, it comes back running /w no tilt. So far, the customer service seems good (a lot different than calling JAC up for sure :lol: )"
Posted :: 12/11/2008 11:38:50 AM CST

 I would like an update from the OP as to whether the gun and/or parts have been sent in as requested. If this is going to be a fair evaluation then the parts should be sent in and evaluated and TNW be given a chance to make things right or point out the mistakes the OP made in his installation of the product so we know for a fact who is at fault here.

I have to believe that if 1300 of these were sold and this was an outstanding issue, we would have heard alot more complaints by now, doncha think??

Even if you aren't a fan of piston kits, don't you think it's only right to be fair??

Once again, not to bust the OP balls, but let's finish this evaluation by letting the manufacturer have their say and a chance to make it right.

Just a note: I have no affiliation with Weaponeer or TNW and stand to benefit nothing by this post. I want to see it resolved no matter who comes out on top.

As a matter of interest, I installed mine a few days ago and today had the brief opportunity to pump ten rounds down range into a stump in a local wood line.   It performed without hiccup through my RRA Entry Tactical.

More range time is coming up in the next week or so.  I just couldn't allow it to sit in the safe until it had a proper throttling.  

BLUF- The kit works but be prepared to mod your rails if you want to add all the ornaments back to your system.  Another highlight is that the manufacturer is willing to entertain phone calls and as a bonus seem to be genuinely concerned about your particular issue.

Lows-  Instructions are less than desirable. I've offered my PowerPoint and adobe ranger skills to the folks at TNW and I believe they are going to allow me the opportunity  to re-design and re-word the document to make it a bit more user friendly.  There isn't a boiler plate on the document that lists the kit contents or a numbering system for the process.  Mine was missing a 6x32 x 1/2 cap bolt, so I had to drive to the local Mom and Pop hardware store and pick one up.  Lowe's and Home Depot didn't stock anything under 8x.

When the smoke clears I believe that it's going to be a hot seller.  More to follow after I mod the quad and put an assortment of ammo through it.

Happy New Year and Godspeed

Hawk Pilot

GREAT THREAD!

Is this the same TNW that puts out poorly made m2hb and m3hb 50 cal guns?

Only in inexpensive CONVERSIONS. FMJs-of-Freedom

What happened with this DavePAL84?