HK MR 223 Upper /AR lower build??

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Superchunk

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Looking for advice on a new build, using the HK MR223 A3 upper, and a mil spec AR lower.

Firstly, I'm doing this for a few reasons. I like the HK MR223; tried one and liked it. I love my DDM4 with a Geissele SD3G trigger and Magpul furniture, and I love the new Giessele rail. So I want to build my new rig based on the best of both.

I've done some searching, but it's lots of armchair rhetoric and BS. So I'm asking you fine lads here.

I know there are other piston options, but I do like HK products, and want to stick with them.

Questions:

1. What premium AR hand guards are compatible with the MR223? Is it HK barrel nut specific?

2. Can I use a Mil-spec lower, equipped with an aftermarket AR trigger, like the Geissele SD3G??

3. Can I use an AR BCG, or is an HK specific bolt required?

4. Are there any options for upgrading or changing the gas block on the MR to an adjustable??


Any insight greatly appreciated, thank you!
 
1. HK must use handguard built for HK MR556 or HK416
2. Geissele SD3G, or any regular geiseele triggers will not work with HK due to the firing pin safety. You must use a Geissele HK trigger or a regular mil spec trigger/hammer.
3. No, HK BGC is proprietary
4. No - HK gas block and gas system shall not be tempered with.

In general, factory HK upper kit comes with the full upper and the buffer weight and spring. There is no such thing of buying the bare upper and stuffing after market parts from various shops into the upper to make it work.

Well I guess brownells have some US made parts now, but they are only for HK or their HK knock offs.
 
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I can say from personal experience that a PWS lower will not fit a MR223 upper that has a Midwest industries handguard. The handguard prevents the lower from going forward far enough to allow the front pivot pin to be inserted.

I dont have any other handguards to try.
 
KAC trigger groups work in HK 416 / MR 223's, I have two of them in mine.
Yes a few vendors had barrel / upper / gas piston-rods for sale. HK sells those as replacement parts and the barrels often come with the gas parts and bare upper receiver, but no bolt group or hand guards.

Rich
 
I run my upper(s) on a BCM lower and Umbrella. I use ALG triggers, no problem. Handguards are mostly HK and Geissele. I've use a company in Germany for HK parts, a bit of wait for them to get the permits and ship but it was no problem, just order online and they take care of the rest. Good luck. I don' personally see much point in a adj gas block unless you're running a suppressor?

Also HK416 BCG aren't "backwards" compatible, meaning they won't run in a commercial MR223 or MR556 because of the barrel extension "notch" however a MR BCG will run in a 416. So if your sourcing a BCG just remember that.

HKPRO had a thread on compatible triggers


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When you put the HK upper onto some other lower, is the HK buffer spring necessary? Or can any other spring do it(say, a super42)?
I should also mention im using H3 buffer
 
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Tiker said:
When you put the HK upper onto some other lower, is the HK buffer spring necessary? Or can any other spring do it(say, a super42)?
I should also mention im using H3 buffer
Click to expand...

IIRC HK recommends there heavier buffer and spring due to the increased velocities the gas piston creates. I believe that's why there uppers come with the buffer and spring. YMMV.

I'm guessing not using there buffer and spring could caused a warranty issue? & I've read that it can cause damage to the upper, lower , pins, and disconnector?
 
mildot said:
IIRC HK recommends there heavier buffer and spring due to the increased velocities the gas piston creates. I believe that's why there uppers come with the buffer and spring. YMMV.

I'm guessing not using there buffer and spring could caused a warranty issue? & I've read that it can cause damage to the upper, lower , pins, and disconnector?
Click to expand...

Well, the uppers being sold up here dont come with buffer and spring.
The H3 buffer is already heavier than factory HK buffer.
The super 42 seems like it gives less resistance than the HK spring though...
Dont see any stores selling the HK springs up here neither
 
Tiker said:
Well, the uppers being sold up here dont come with buffer and spring.
The H3 buffer is already heavier than factory HK buffer.
The super 42 seems like it gives less resistance than the HK spring though...
Dont see any stores selling the HK springs up here neither
Click to expand...

I see your point, from what I've read its seems to be about owners "tweaking" there rifles to fire suppressed and unsuppressed, and reliability? I'm sure that various after market combos will work.

I'm guessing that you would have to order the buffer and spring from a "dealer" etc.

When I built my rifles I used HK buffers & springs and there receiver ext as well.
 
Was hoping some one here has tried a Mr223 or 416 upper on a regular lower and can share their experience.
If not, guess im just gonna have to find out by firing and checking brass ejection pattern and checking for wear and tear
 
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