Does anyone know if the Osprey piston system will fit under the Seekins MCSR V2 rail AND work with the barrel nut?. Building a piston 6.8 SPC.

It will fit but you need a FF op.rod from osprey

THANK YOU!, so do I just contact them directly? Or is there a site I can purchase this from?

EDIT: 6.8mm gas tube any larger in diameter?

I was just going to post on this subject in thanks for an archive post I found here on ar15.com about Osprey compatible guards. I was really doubting my decision to install the kit because I was having so much trouble finding a decent guard. One company I called which was specifically mentioned by Osprey wouldn't even return my sales inquiry and never answered their phone.

Result? I purchased the MCSR V2 Mod Rail (http://www.seekinsprecision.com/parts-and-accessories/handguards/mcsr-v2-mod-rail.html) and installed it last week. Best price I found was from Joe Bob Outfitters online, they're based in Kansas.

I had no issues with the stock operating rod, so I don't believe a modified op rod is required. You do have to make sure you have the correct lineup between gas block and the barrel nut/upper. If the piston system doesn't slide freely with the touch of your finger, then you don't have it lined up correctly. With the bolt open, I can tilt my AR and the piston system slides freely back and forth. The Seekins barrel nut comes with 2 shims which will help you adjust the nut if it doesn't line up correctly without them.The nut is aluminum so be careful with your wrench.

I do like how positively the rail locks up to the upper. In a word, it's seamless. The first time fitting it over the nut I used my soft mallet to nudge it into position. In this picture I was still tinkering with the Keymod rail grip sections. Took the rifle out this weekend and it ran great. With the kit, it's the easiest of my AR's to clean after a range day although I would probably go with another piston manufacturer in the future if I wanted more FF options.

http://i1383.photobucket.com/albums/ah297/heavybombers/DSC_00054_zps0a8f6597.jpg

I am almost positive it's the same diameter as the .556, thank you for helping me out bro! I really appreciate it! That is a sweet ass wepon you built! All of my parts should be in by Thursday so I will see how this build goes!

On the photo below, left is a std barrel nut oprod and right one is a free float barrel nut oprod

Ah, that image is very telling. The non standard allows for more travel through the barrel nut. I'll have to pull the guard off to look, but suspect I better acquire one.

Any idea what Osprey is asking for the replacement, or if they've been responsive to such requests lately?

I got mine about 2yrs ago, it was somewhere around $45

I guess you built a super short stroke piston system.. JK

No kidding!  

It's long enough to work, but I can't imagine banging into the nut is very good for the long term health of the piston.  

I can answer my own question. The non-standard op rod is $56 + shipping. Call them at their listed number (it's on the web site) at gaspiston.com

I bought the 416 Fail Zero with the op rod for $357 shipped directly from Osprey....not bad I guess...I'll see how it all works out. The guy at osprey said if it does not fit or I'm not happy he will refund me 100%! Good customer service..

When did you buy it?  I picked mine up at the NRA convention in April,  The President of the company gave me his business card, with email, three phone numbers, etc.  I have tried to call/email to ask questions about hand-guards multiple times--no response.