I have an HK MR556. It’s only got about 150 rounds though it, but ever since day 1 it has been ejecting brass sharply forward at the 1-2 o’clock position (usually closer to 1 o’clock). As you can see from the image below, a lot of the brass actually seems to be catching the rear of the ejection port window, and not the actual deflector. Have shot M193 and M855, and it seems to be worse with the M855 ammo. Haven’t had any malfunctions as a result, but want to see if there is anything I can do about this. Have seen a few comments that this rifle runs ‘overgassed’ out of the box, but not sure how much truth to that statement.
As there is not gas setting on the HK MR556, any ideas on how to remedy this? It is running all stock parts except a BCM compensator. Has the heavy HK red dot buffer (5 ozs I believe), as well as their heavy spring (both came stock), so not sure I can slow the bolt down at all.
Any info or similar experience with this rifle is appreciated. Have posted on HK Pro site, but had limited responses so I thought I’d try here.
Both of mine eject M193 in the 1 - 2 area as well as I recall, perhaps more toward the 2:00 than the 1:00, but I shoot mostly reloads with my brass catcher attached.
I’d say you have no problem and to keep shooting, especially since it isn’t malfing. In fact, consider yourself lucky it isn’t slinging them 50 yards to 1:00 like my HK91 does. Try some PMC bronze and see where that round lands.
It will settle down a bit with more rounds down the tube.
As you say, it is cycling fine. If you want to try to move ejection further to the side, and it can be nice at a shooting range to not have your brass going ahead of the firing line, give a more powerful spring a try.
Well assuming that the MR556 is similar to the HK416, by design it is overgassed, because it needs to additional gas for it to cycle. Unless it is malfunctioning, I wouldn’t be concerned, but I also know people can’t leave things alone or have OCD and will want to try and fix what isn’t broken. I would possibly look at a different spring from Sprinco.
HK designs and their clones are notoriously hard on brass for the sake of reliability. Yeah, that’s the way they were designed, but it doesn’t mean it is strictly necessary for everyone who buys the rifle. It isn’t OCD for an individual to tune their rifle outside of what HK intended as long as it works.
Also, if it needs the extra gas to cycle, then it is gassed correctly. The very concept of a gun being over-gassed means that there is too much gas.
Your MR556 is functioning normally, or as close to normally as I’ve seen 416s extract and eject.
I would keep a close eye on piston ring wear, then the bolt lugs and the tail of the disconnector if you’re using the original hammer/trigger/disconnector.
The buffer spring should be serviceable for multiple thousands of rounds.
Regarding the buffer spring, is the stock HK spring a heavy spring? I’m assuming since the HK buffer is a heavy style that they made the spring a little beefier too?
The spring compression is heavier and length is longer as well. As long as can be inserted in the extension and still compress far enough to work.
A few months ago, I’d give you actual dimensions from a new spring, but too late now.
So I picked up some PMC Bronze like you guys suggested and tried it out yesterday in the HK. It seemed to do the trick. After about 60 rounds I looked over and saw most of the casings sitting in a pile around 2:00/2:30 area as opposed to forward of the firing line. Stuff seems to run low on pressure scale as suggested.
Wasn’t aware they even made an adjustable block for the 416. Is it an HK made part or after market? I know they have different gas blocks for the various 416 barrel lengths but haven’t ever seen a legit adjustable version.
