Mr556a1

Why bother to have 2 versions? This is blowing my mind!

I bet they started out proprietary, and then realized from their US division that they should make it compatible with other "high quality AR style" firearms. Then they did the second version.

Blows my mind too. This seems like a very HK decision if this is true.
 
The sign says it will be interchangable with other AR lowers,so what is the story here?

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Photo credit: SMGLee taken from M4Carbine.net

The sign says it will be Interchangeable with other High Quality AR-Style Firearms.

Knowing HK, that might actually mean THEIR other AR-Style firearms. The ones made by them:D
 
From what I understand the MR556 exists in the US because they cannot import the MR223 from Europe like we can. To get around the US regulations they have a "US made" MR556 (like the MR223) to get around that.
 
The MR556A1 is compatible with standard AR take down pin location.

16.1" barrel, Daniel Defense made rail. etc.

No SBR plans at all, as LE/MIL can get Hk416's
 
Took a good look at the rifle at SHOT and frankly the POF, KAC, LMT, Larue all looked more interesting. Honestly the HK booth was the one that disappointed me the most at the show. Triggers were heavy and mushy, ergonomics kinda blew and the gun is pretty heavy although thats to be expected.

I understand the hype as HK has brought us some pretty interesting stuff in the past but I'll pass on their AR. There are equally as good products out there for less $, POF's guns come to mind.
 
Took a good look at the rifle at SHOT and frankly the POF, KAC, LMT, Larue all looked more interesting. Honestly the HK booth was the one that disappointed me the most at the show. Triggers were heavy and mushy, ergonomics kinda blew and the gun is pretty heavy although thats to be expected.

I understand the hype as HK has brought us some pretty interesting stuff in the past but I'll pass on their AR. There are equally as good products out there for less $, POF's guns come to mind.


I'll take the properly engineered HK over any half assed conversion with bolt tilt issues any day.I've shot the 416,it is not your average AR in terms of fit and finish as well as performance. The MR556 is a disappointment with it's issues well known,however, I'll take an MR556A1 upper over any other piston system out there.
As for the POF..not in a million years.
 
Yea I can understand that, in the end though why not just get a good quality AR in the form it was engineered to be :stirpot: :D.

If I were to pick up a 556a1 I'd pass on the lower and just stick with the upper.
 
Yea I can understand that, in the end though why not just get a good quality AR in the form it was engineered to be :stirpot: :D.

If I were to pick up a 556a1 I'd pass on the lower and just stick with the upper.


Thanks got 8 of them already. I was talking about the upper only ,as I have 2 more lowers missing uppers.
 
Thanks got 8 of them already. I was talking about the upper only ,as I have 2 more lowers missing uppers.

Be careful about putting the HK upper on a non HK lower. Assuming the MR556a1 has the same firing pin safety as the HK 416 and the HK MR223 (reasonable assumption IMO), many hammers will not function correctly with the HK upper. You need a relatively tall hammer with no cut-out on the top front of the hammer. The cut-out version is often found on semi-auto triggers and the no cut-out version is necessary for select fire triggers.

Pic of one hammer that apparently works to deactivate the firing pin safety (top) and one that doesn't (bottom):
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Here is a picture of my MR223 hammer:
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Note that the trigger is relatively tall with no cut out on the top edge.

Here is the same hammer from the top:
imgp0870.jpg


Note the silver wear mark top centre of the hammer. This mark is caused by the hammer depressing the firing pin safety just before the hammer strikes the firing pin.

From the MR223 operator's manual:
"Pulling the trigger releases the cocked hammer. Just before the hammer strikes the firing pin, the hammer releases the firing pin safety. The firing pin strikes the cartridge primer."

Without a tall hammer that lacks a cutout, the firing pin safety will not be released and the firing pin will not be able to travel forward.

Again, this presupposes that the MR556a1 hammer/firing pin safety interface mirrors the MR223 and HK416 hammer/firing pin safety interface.

I ran into this issue while shopping for a Geissele trigger. The SSF (select fire) version has the high shoulder and would definitely work, but is very expensive and hard to source. I was going to try the SSA version (cheaper and easier to get eg http://armseast.com/store/index.php?main_page=index&cPath=49 ), but didn't feel like risking $250 for something that may not work.

I'd still like to get the Geissele trigger. Has anyone tried the SSA version in a MR223?
 
Which brands use the neutered hammer? My LMTs all have full hammers. I wonder if there is a chart floating around.
 
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