I've been working on this off and on for a while now, and I recently had some time to finish it up.
1) Where can I buy a 416?
In short, you can’t. True 416’s are only sold to Government and LE agencies (no longer to individual officers). But all is not lost as you have options (in order of increasing expense):
- Get an MR556A1 upper kit and use it on a mil-spec lower
- Get a complete MR556A1
- Get a “gray” market 416 upper and use it on a mil-spec lower
- Get a “gray” market 416 upper and an MR556A1 lower
2) Where can I find a true 416 upper receiver?
The best places are the HKPro market place, Gunbroker and Sturmgewehr.com. However, new 416 uppers are becoming rare because HK policy has changed to prevent individual officers from purchasing HK rifles and selling off the upper (gray market). Expect to pay upwards of $3500-$4000 for an upper in good condition with sights, buffer & spring. 80% uppers like the 14.5” trade-in uppers from NASA or the 10.4” PD trade-ins with Surefire flash hiders (obviously used with suppressors) that don’t include a buffer or buffer spring sell for about $2500. (NOTE: these are basic market values at the time of writing and may vary with time)
3) Is it legal for me to have a 10.4” or 14.5” upper?
Mostly yes...but I would advise proceeding with caution when NFA items are concerned. An upper doesn’t need to be transferred like an AR lower. However, one must comply with NFA rules and regulations if you have yet to complete Form 1 for an SBR (short-barreled-rifle).
4) Can I have a 416 upper without having it be an SBR?
Yes, you can permanently attach a variety of muzzle devices (per ATF specifications) to make the overall barrel length over 16” in length. Obviously this poses more of a challenge with the 10.4” barrel. You can also put the upper on a pistol receiver.
5) Is there a 16 or 20” 416 upper?
Currently, the Marines field the M27 which has a 16.5” barrel; as does the 416N (Norwegian variant). 16.5” variants do exist, but most (if not all) of the “gray” market uppers in circulation are 10.4” or 14.5”. I have only ever seen one 20” upper for sale ever (priced at about $6k due to rarity). HK reps simply state: “they're in the lineup, but no one simply wants the 20”
6) I heard that my MR556A1’s barrel isn’t chrome lined…WTF?
This is true barrel blanks were shipped from Germany and finished here by Daniel Defense. Many speculations have been made about why, but most don’t consider US import restrictions, the ’05 barrel ban, and German export restrictions almost certainly play a major roll in this matter.
7) My MR556A1 has the OTB (Over The Beach) drain holes in the receiver extension (buffer tube), it must be OTB!!!!
NO!!! Your MR556A1 is NOT the same as the OTB variant. True, there are drain holes in the receiver extension AND the carrier for production logistic reasons. However, the MR556A1 lacks the necessary modifications to the chamber face and barrel specs to ultimately help keep the upper receiver (and your face) in one piece. Furthermore, the rifles are not OTB tested and certified by HK.
8) What’s this loop on the bottom of the gas block for?
That is for mounting the M320 40mm launcher. The launcher attaches to the rail and a cross-bolt (like a bigger version of the push-pin on an AR lower) goes through that hole and secures the launcher in place. If you have an MR556A1, you have the same rail and gas block as the 416 only with the sling loops and bayonet lug removed.
9) It looks like there are a lot of front and rear sight options. How do I tell the difference?
For 5.56mm guns, there are 3 different rear sight drum options an currently 1 folding rear option. The 3 drums can be distinguished by a series of dots under the “2” aperture. “.” For 10.4”, “..” for 14.5/16.5”, and “…” for 20”. There are 2 folding front sight options: 33mm and 28mm. The 28mm is for use with the drum rear sight. The 33mm is per Norwegian specs and for use with the folding rear. Currently, a folding rear can not be used with the fixed/picatinny-mounted front sight.
10) Which mags will work in my HK-made lower?
Obviously, HK mags will work; as will GI aluminum. PMags; unfortunately, will not work because of the magwell dimensions. Some have been able to remove some material from the front of the PMag to make it fit. EMags will work fine in HK magwells. Beyond that, the discussion of what is “best” is more or less personal opinion.
11) How do I attach a sling to my MR556A1 without the loops on the gas block?
First, attaching a sling directly to the barrel in that fashion no longer makes it free-float; you are better off without them. Choose and aftermarket rail mount and go from there. Don’t feel obligated to use the factory 3-pt as numerous, viable options exist.
12) Is it true I don’t have to clean a piston gun?
No, you still need to clean and properly lube any firearm with moving parts. The bonus is that parts stay cleaner, cooler, and hold lube much longer than a standard AR15.
13) I read on AR15 about carrier tilt…is this an issue?
No. HK has made modifications to the carrier and a few other areas to make this a non-issue. That said, the 416 is not 100% perfect. The operating system increases bolt speed which has a chain of cause-and-effect issues that HK has done its best to address and correct. The bridge protecting the disconnector on the MR556A1 and newer 416’s is an example of HK’s ongoing efforts toward their products.
14) I saw on a video where I can use the bolt lugs to tighten the handguard screw, should I do that?
I would avoid it if at all possible. I see no need to put undue stress on bolt lugs for that reason. If you must do it, it is advised to use the lug opposite the extractor.
15) How do I remove carbon fouling from the piston?
Carbon and discoloration isn’t a big deal on the piston. DON’T scrape it off with anything sharp and damage the piston or gas rings. So long as the piston rings are viable, you’re good to go. If you must, use a Scotch-Brite pad or maybe some solvent and elbow grease. To check the viability of the rings, insert the piston into the gas block without the pusher rod assembly installed and hold the upper/rifle vertically (muzzle up). The piston should stay in the gas block. If it falls out, change the rings.
16) I installed an HK upper on my non-HK lower, and the gun won’t fire!
To reduce the risk of slam-firing, HK installed a firing pin safety. To disengage the safety, you need a mil-spec style hammer without the “cut-out” at the top. Otherwise, the safety will not disengage, and the firing pin will not be struck by the hammer; thus, it won’t fire.
17) What if I remove the firing pin safety?
It's recommend this as I have mentioned the increased bolt speed and risk of slam firing (especially with primers that are improperly seated).
18) What about match triggers?
Again, a certain amount of hammer speed is required for reliable primer ignition while disengaging the firing pin safety and acting against the firing pin (not found in standard AR's). Some are not built to withstand the increased force/speeds associated with this system over time. Also you need to make sure the hammer is the appropriate height. Montrala
has formed a comprehensive list of triggers that have been tried in HK guns