So I used to have an MR556 worked as close as I could, but I wound up getting out of HK’s for a while.

Got the itch the other day, and decided to start another “416” build. I was rusty on the HK stuff, but it’s coming together faster than I thought it would.
Parts I’ve snagged:

Unmarked 416 stripped upper from HK forging
HK FA
Colt dust cover
HK Haus Bushing
Geissele SMR (the original)
Geissele DDC SCH
KAC 99051 irons
416 Bolt
10” Marked HK Unvented Gas Block
Titanium firing pin
Nefarious 10.4” 416 Barrel
HK Gas Piston
Surefire CT Warcomp
Colt Cam Pin
Colt Firing Pin Retaining pin
HK Gas Block Pins

Right now, as far as I’m tracking, I just need a piston rod, barrel nut, and carrier. I thought I had a seller for the barrel nut but he started ghosting me... whatever, he wanted $130 for a barrel nut that’s $40 ish on the HK website.

It’s been fun re-learning all the HK stuff. Less fun on the bank account. Probably going to throw a T2, MAWL, and SF600 on it.

Lower will be a Remington Defense SBR lower with a KAC 2 stage, H3, (going to experiment with springs), Magpul Grip, and LMT SOPMOD. Really looking forward to getting it done.

If anyone has any tips or tricks on getting it together that they’ve learned the hard way or aren’t commonly shared please let me know. Or an extra barrel nut.

It's going to be fun finding a bolt carrier... I wouldn't be surprised if you have to spend more than $1000 for it.  I ended up buying an entire MR556 upper to get one, during a brief window of opportunity a few weeks ago.  Good luck.

Thanks. Been pretty lucky so far honestly. Trying to get it done before any uh... potential government intervention.

My goal with this one is to have it run super reliably unsuppressed. Just a straight chopper.

Ideally I’ll be all in at about $2500

I just need a stock and grip, but they are overpriced at HK parts.

I keep missing them on the EE

I’m down to needing a piston rod and carrier.

Someone on Reddit (I hate that place), is selling a V2 grip for $40 shipped I think, and I think someone on HKPRO is selling furniture.

Any ideas on where to snag a carrier and rod?

You could sign up for notification of "in stock" at MidWest Gunworks.  Good folks there with decent prices.........although I wouldn't expect anything anytime soon with the recent democrat tyrants takeover.

Yep - I’m signed up just about everywhere.

I think I have all the parts... can anyone recommend a good jig for pinning the gas block? Or just some wood?

There is no jig.  The barrel is grooved, the gas block has holes, and roll pins (or 'spring' pins) go in the holes.  

How many children did you have to sacrifice for a bolt carrier?

I don’t want to talk about it haha...

Maybe jig isn’t the right word - I’ve just always used a support for a gas block when I’m pinning one. The 416 block is obviously a unique shape, so I was wondering if anyone had any tools to support.

The roll pins on the 415/mr556 go in much much smoother than the taper pins on an ar style a frame. A solid bench is all you need to drive the pins, along with a decent hammer and punch obviously lol. Very secure but a lot easier to set and remove.

That’s outstanding news thanks.

My first one is just about done - just waiting on the flash hider. The second one is just waiting on the upper and lower to be refinished, and a barrel nut and carrier.

Those Marvin Pitts barrels are damn nice, and the coil pins were a welcome change to pinning a gas block, really appreciate the indexing tab too.

The next one will be set up to shoot suppressed. Vented gas block, H3, and Springco blue is what I’m leaning towards.

Brownells has a video on assembling. pretty straight forward.

I started my builds just after T-Day, I look at prices I paid back then and what they sell for today it is like GameStop Stock.

The build was super straightforward, but fun. Taking it out tomorrow I hope to sight in.

Please no hate on the Remington Defense lower. KAC trigger in there.

Remington Defense Lower requires a Remington Defense Handguard!

I had it on my last one and I think I prefer the Geissele. If I build a 14.5, I’ll get another RAHG. Really looking forward to my second one already.

Anyone know where I can find an HK grip in black? Got an RAL8000 one for the one that’s coming together.


Sent the other receiver set out today for cerakote. Colt SBR lower was already raw from having an engraving fixed (thanks ATF).
Hopefully it comes out well and pairs well with the DDC Geissele rail that the other one will wear.

I have been silently watching this thread. Any updates?

Sorry I missed this dude- will get you some pics and testing updates this weekend @nemesismind



This is what it initially came out as.

Since then, I’ve switched on a black Wilcox riser, a T2 on a LaRue absolute mount, a G33, a FP PEQ15 instead of the C, and bumped up the Surefire light.

Also going to swap on an AAC can to test this weekend, see how it runs with that.



Also tried it with the Razor 1-6 for a bit when the 1-10 came in. Pretty good setup actually.