I have a Daniel Defense SBR.  10.3" barrel with a Daniel Defense MK18 10" rail.  Does anyone know of a piston kit that will work with it?  

I emailed Adams about their new lite kit.  And their official response was, we dont know, try it.

It looks like it will work.  But before I drop that kind of money, I want to know for sure it will work.

Thanks!

I dunno if the rail has enough clearance for the piston, but there is only one way to find out.

LOL, thanks!  Thats what they said!

Might wanna wait for the xlp to come out.

After exchanging a few more emails, they finally told me about the xlp.  I will probably be placing a pre order today or monday for it.

Thanks for the help guys

Probably be ordering one myself for an MK18 build also.

I just put together an AA mid length piston kit and found out some of this pain first hand (although the kit went together perfectly).

The kits seem to be designed to work with a barrel nut that doesn't exceed the dimensions of the the standard delta-ring barrel nut. The issue is actually the spring and bushing that goes over the piston rod. That bushing wants to rest against the barrel nut so it's height and length become critical dimensions.

I tried this with a DD MFR 9" rail. The piston itself cleared everything just fine, both the proprietary barrel nut and the hand rail. I was all excited. The problem was that the bushing didn't have much metal to rest against due to the shape of the barrel nut AND the barrel nut is longer than the standard so the spring pressure would be way too high. I could have chopped the spring down but I didn't have a quick way to solve the fact that the bushing was only pressing against the barrel nut with a tiny contact patch of metal.

The website does say that only barrels nuts of mil spec length will work but it doesn't provide enough pictures or info to indicate why. Really, I don't understand companies that have piss poor documentation. Even that video is beyond worthless.

If I can answer any questions please let me know.

-Stooxie

Just found this:

http://www.ar15.com/archive/topic.html?b=3&f=126&t=515358

This illustrates the issue exactly. If you've got a place for that bushing to comfortably press against and the spring pressure is right then you should be ok.

-Stooxie

My setup looks exactly like the picture in the link you posted.  Hopefully it will work.  My kit will be here tomorrow.  I already have the gun tore down waiting for it.

If it works good on my SBR, I will install one on my 16" 5.45x39 rifle that has a 12" daniel defense.  I hate cleaning it.

As first-hand experience you do need to make sure the bushing and spring clear the barrel nut.  In hind site to a slightly warped op-rod I realized that mine was putting just a little pressure on the rod while riding on top of the barrel nut for my Diamondhead VRS-T handguard.  Over time it put a slight bend in it until it wouldn't run.  After a bit of clearancing on the barrel nut and on the spring bushing on the op-rod itself it had run flawlessly for a few thousand rounds now.

To their credit AA took care of me with their fantastic customer service right here on the arfcom.  Can't beat it when they come to you about an issue.

I installed the XLP kit last weekend.  The bushing looks fine.  The gas block is very snug under the rail.  I guess it doesnt matter.  I just isnt a free float any more

Can you post some pics of the DD rail and gas block ?

I will when I get back in town.  Im in the southern part of the state doing a gun show.

I took the SBR out today on my inlaws land to try it out for the first time this afternoon after the gun show, and it wouldnt function.  It acted like it was short stroking.  It was kicking the shell out, but it wasnt picking up a new one.  I didnt watch the instructional dvd when I installed it. I assumed I could figure it out myself.  I didnt use the guide rod.  So my best guess is that something is binding up.  Hopefully the tight fit under the rail doesnt have anything to do with it.

I will get pictures to you guys sunday night.

If the rail is rubbing the gas block it could be rubbing on the drive rod. One way to check for clearance is to assemble everything but leave out the rod spring and bushing, if all is well when you tilt the rifle the rod will move back and forth freely. This same check will tell you if you have the gas block lined up straight with the receiver, if its canted just a little it will cause the drive rod to bind. I advise watching the dvd also.

Thanks for the advice.  

Its very possible that the piston is rubbing on the rail, there isnt much room in there.  Ill know more when I take it all apart tonight.  Im sure I will see signs of rubbing.  Ill take pictures as I take it apart so others with the same setup can see what is going on.

The piston isnt rubbing on the rail. The gas block is defiantly snug under the rail.  I found my problem.  Im an idiot, I forgot to put the bushing inside the receiver......   I wouldnt think that would cause the short stroking, but who knows....

Also, there is 6 settings on the piston.  The rail only allows me to set it on setting 5 of 6.  I doubt that would cause me that much trouble, but who knows.






As you can see, the Daniel defense MK18 rail will only allow me to set the piston to setting #5 of 6




Pulling the gas block through the rear of the rail.  The piston is still installed on the gun at this point.  You can see how tight of a fit there is with the gas block and the inside of the rail.




Rail completely off

Nice !   ,   I think a little minor milling ( I hate to say dremel )  at the front of the rail will help clear the block and the gas adjustment, it sure looks very tight at the sides of the top rail and I would be concerned about hand guard movement hitting the drive rod.   Make sure you have the proper "gap" at the rod and gas block. This gap keeps the rod from being hammered  into the gas block and the carrier from being hammered into the rod .

I like the way the rail comes off without having to take the gas block off. Thanks for the pics , now that Michigan repealed the SBR law I was looking into a MK18 set up , so thanks for being the Guiney pig on a new product.