So I think I need a new project and have my eyes set on a piston SBR. I always loved the look of he Hk sbr 416 but don't quite have the couple thousand to drop for one. So, I'm thinking about retrofitting a sbr upper with piston and rails etc. to make a customized approximation. I've browsed around for information but it is a bit of an overload so I'm just going to ask a few questions here and see if  I can get some good starting points. Cost is an object here (I don't expect 300$ all in obviously, but the lower the better...especially if I'm spending for a sbr permit).
So I need to find a low profile gas retrofit system that's fairly reliable and can fit under a rail system. I've seen the Osprey system but I worry about cleaning with it. Do you have to remove the rails to clean the piston system? Also are Yankee Hill rails good for these systems? I have some experience with Yankee Hill and the price point is right. My last question is do these systems work well with 6.8 ? I'm considering a new chambering for this project as I already have plenty of 5.56.  So what are your thoughts? Think I'm crazy for trying to bring this project in without selling all my worldly possessions?

You can buy Adams Arms, or you can buy shit that's eventually gonna break.

At the rate transfers are going right now... you will have a good deal of time to save up for an upper while you wait on your stamp.  

Good point on the wait, I've heard they don't have a very quick turnaround time. Dan, I respect the opinion but you say a.a. someone else will say cmmg or one of the many other companies out there will be the only reliable option.  Adam arms is def. up for consideration, as is cmmg and osprey. I just wish the cmmg and Adams units didn't have such bulky gas blocks

Yep, they will. And while I KNOW AA to be the most reliable piston out there, I don't have any interest in anyone buying it. Not even the interest of defending what I own. I run only DI right now. I may go piston later on my SBR, and if I do it'll be Adams Arms.

Yes you'll have to take the rail or handguard off to get to the piston system. Dont get hung up on the rail covering the gas block, there are rails that surround the piston gas block . The look is different but the results are the same. See the AA website for a look at their new lite piston rifles , they now sell the lite piston kits also.

I can also recommend Adams Arms. The kit I have is amazing, and the ability to change the amount of gas (although I don't use it much) is greatly appreciated for when I finally get around to getting that suppressor.

And, you won't really have to remove your handguards to get at the piston, depending on the system. With Adams Arms, you pull the whole piston out of the front and can clean it that way (if you ever need to or want to I guess.)

I also like the railed gas block up front anyway since I wasnt going for a pure lightweight build. It allows me to put whatever irons I want on it, including flip ups and such.

Osprey system with a pinned or (set screwed with dimpled barrel) gas block under a Midwest Industries midlength piston rail.  Running that set up on my 10.25" sbr for 5000+ rounds with no problems and never cleaned.  Its all a matter of preference.