I am interested in buying a MR556/HK416 Stripped Upper Receiver and building a clone/clone like (As close to the 10.4 Style 416 SBR, which I would like to use the Geissele HK SMR Rail meaning I would probably have to have a 10.5 Barrel, could be very wrong on this aspect in barrel length though) in 6.8 SPC as stated in the title, is this feasible, could I buy the upper and acquire a 6.8 SPC barrel and will it fit the upper receiver with HK Barrel Nut, is it compatible with the Gas piston system, what would I need to do to make this a reality, I'm sure I will have to do custom barrel work to be able to make it compatible with the Gas Piston System as well as the HK Barrel Nut, and if so is there anyone capable of doing that work? Do I have a shot at being able to do this, or is this a pipe dream? I think an MR556 SBR/HK416 Clone SBR in 6.8 SPC would be awesome as hell, and is the holy grail of AR15's to me, as stated, is this just an absolute ludicrous idea, or do I have a shot at it. Thanks for any help and information provided, and apologize ahead of time if this belongs in the HK Sub Forum.

Thanks!

It is do-able, but it is going to be expensive.

There are some smiths out there to would be able to profile a barrel and set it up for the HK gas block.

You will need also HK barrel extension for that to work.

So basically you need HK MR556 with worn out barrel and then have custom barrel in 6.8 SPC made to it. Finetune gas system and you are GTG ;)

Thanks for all the responses! I appreciate the help guys thanks!

Anyone that would create that kind of barrel profile for it?

This would be badazz

Yes thank you for sharing the enthusiasm! I think it would be bad ass I wish this could turn into a collaboration type thread and get it going I so want this!

There were some guys at HKPro who were making replacement barrels for HK. Have a look at HK416 subforum there.

It seems to me that you are not very serious, as if you were, you would already have the ball rolling on the project.

You have would have decided if you were going to go with a 416, or settle for the MR556.

Then you would buy the appropriate gun/kit parts.

IGF or MP@NA could profile the 6.8 barrel of your choice with a rifle length gas system and a medium to heavy profile to work with the HK gas system.  The big question would be the right gas port size.  Might be best just to pay the smith to figure it out and test fire it.  MP@NA already has experience replacing MR556 barrels with AR15 barrels.

Seriously man, you could probably have had it finished already if you actually wanted one.

I like you asshole! Maybe I oughtta just show you up and buy one of those stripped uppers, which I'm currently saving up to do because I have an addiction to AR15s, I'm currently really liking the idea of a gas piston AR. All honesty though, I am strategically planning on what I should get first, the harder to acquire parts like the gas piston system parts and full HK416 stripped upper, but I will look into IGF or MP@NA for the barrel reprofile but where would I get that kind of barrel to start?, I just want to take care of the time consuming expenses first with the harder to get parts, and yes I want the HK 416 stripped upper. I really don't know what order to go into but I'm hoping to purchase the HK416 Stripped upper here in the next week or so, I just don't know where to go after that. But thanks for egging me on for this one, I don't want it rifle length I want it to eventually be an SBR come February I'm taking my tax refund and getting tax stamps on 3 lowers of mine and I would like to make the HK lower one of those stamps, I don't know where to get one though. That's one of the conundrums I'm faced with, I do know where to get the upper though which I have in my cart and will be purchasing as soon as my next check clears! I'm just finished a .300 Blackout with everything I need, and that lower will be getting a tax stamp come February, and another Spikes Tactical Lower will be getting one too, If I could find the proper HK lower I would be able to get the ball rolling on that one. Like I said just don't know where to go after getting the stripped upper, and have yet to find the lower. Yes this definitely serious help me out then brother!

I had a MR556.  I still have two burst MR556 barrels in my parts bin.  Glad to be rid of it.

I don't think you read my post carefully.  The 6.8 donor barrel will need to either be custom made, or a cut down rifle length barrel.  The 416/MR556 has a gas port in a different location, so it is better to cut down a rifle length barrel.

I think I get you're gist, but I may be wrong but I've been looking at www.hkparts.net and I see they sell the barrels with gas block/holes pre drilled and attached to gas block at different lengths ready to go, so its better to get one at rifle length and cut down as needed to be as accurate as possible with the gas block pre attached at 8, 9, etc etc inches?, which would still require and custom made 6.8 SPC barrel in 14.5-16 inches or full rifle length as in 20?, and I apologize I'm still researching into this, and don't quite know how the 416 functions specifically, have an idea, but most of my research has been through videos of people taking it apart, me reading others posts in regards to the 416 and HKparts.net, I know thats lacking and I'm a big reader just not when it comes to technical stuff, more of a hands on kind of person if that makes any sense, so sorry if I come off as full retard in regards to this subject but I do appreciate you're input, and sounds like you're not a big fan of the MR556/416, but like the fact you took the time to respond, sounds like you've gone down this road that I'm beginning to travel, and could be wrong again, but it sounds like you're saying its not worth going down that rabbit hole?

Edit: I'm a fucking idiot, reread over you're first post I got you on the barrel! Read to quickly the first time my bad was in hurry!

Fastest route would be pick up a MR556.  Send the upper off to one of the two smiths I mention.  Have them take a 6.8 barrel and reprofile it and drill the port as necessary.  Might need a spacer for it too.  MP@NA already makes these spacers.

But your going to have a super expensive bastardized MR556.

If you want the M416 markings and the like, you will need to spend EVEN MORE.  Buy a MR556 and a 416 parts kit.  Throw away those cheap daniel defense barrels and have a high end custom 6.8 made and installed and you will be set.

But in the end, you are going to end up with a very expensive gun with less resale value, that has no guarantee that it will perform well.  It is going to be worth less than what you spend on it.

But hey, it is your money.  I've spent my money on stupider things.

Fuck way to be a dream killer there bro, negative nancy on some steroids over here lol, appreciate the brutally honest response. So is this even worth the investment I know you are saying its stupid but is it at least 60-40, 60 being in my favor or what am I looking at here odds wise this would work out for me for under $3.5k? buying it piece by piece, mind you have some parts in my bin laying around that will work with the lower and or upper.

I have no clue how much it will cost.  I'm not one of the smiths who will do the work, I can't right you a quote.

You have contacted both of them, and gotten a third quote for the work too so you can get the best deal, right?

I also can't tell you if this is a good deal for you or not.  You know you, not me.

Is this something you will buy and cherish forever, or is it just the latest flight of fancy?

Something I've wanted for myself for awhile, just got into building my own franken-AR15s and am still very novice, and I started doing those builds myself early this year, since I've started this has been the one I've wanted to work towards most, don't care if the re-sale value is shit, because I don't want to sell it, if it runs smoothly, but got me worried I'm going to get stuck with a possible piece of shit I might have to part out if it doesn't work. I've contacted IGF, but cannot find MP@NA at all, thanks for the response my favorite debby downer!

Marvin Pitts of Nefarious Arms.  He did an awesome job cutting down my MR556.  He has a page on FB.