5.56mm in 1st Gen HK MR223?

Bartok5

Bartok5

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Hello All,

I did a search without result, so here's my question. Specific to the 1st Gen HK MR223, are these rifles chambered to handle 5.56mm? We all know that .223 Rem and 5.56mm NATO are not the same animal and that it is generally safe to fire the .223 in a (higher pressure) 5.56mm chamber, but NOT necessarily vice-versa. Hence my concern about firing 5.56mm in the MR223. My MR's barrel is laser etched "HK .223 Rem" on the underside, just forward of the Gas Block. There are no other markings.

I really can't see HK manufacturing a rifle that is incapable of chambering and firing the more common milsurp 5.56mm round. Am I way off-base here? I just obtained a Gen 1 MR223 and have not yet fired it. I have both .223 Rem and 5.56mm ammo on hand, and out of due regard for safety I will use only the .223 until I hear otherwise. Still, it would be nice to know if 5.56mm is also OK to use in the MR 223, as I typically buy 5.56mm when I can find a good bulk deal...

Thanks in advance for your informed input. Much appreciated!

Cheers,

Mark C
 
It's all about the throat, they aren't loaded to higher pressure. There is a possibility that an old 1 in 12 twist bolt gun might have a freakishly short throat, but any new rifle with a 1 in 9 twist or faster rifling won't be a problem. I've fired SS 109's out of every 223 bolt gun I've owned and not one sign of excessive pressures. If it was a tight chamber in a Bench Rest gun I may have a concern but an HK? I'll test fire it for you if you like...

Just to clarify, I can pretty much find a .223 load to match any similar 5.56 load re projectile and MV. Therefore same pressure...
 
Thanks for the replies, fellas! Particular thanks to Redshooter and his clarification regarding throat lengths versus chamber pressures. I figured 5.56mm ought to be good to go in an HK civilian copy of the 416, but it never hurts to ask. Off to the range we go....
 
Bartok5 said:
Thanks for the replies, fellas! Particular thanks to Redshooter and his clarification regarding throat lengths versus chamber pressures. I figured 5.56mm ought to be good to go in an HK civilian copy of the 416, but it never hurts to ask. Off to the range we go....
Click to expand...

If you don't do it already it's always a good idea to check the primers of the first few rounds of a new batch or different load for pressure signs. Factory ammo is pretty consistent, but since I reload it's a habit I apply to every new batch I shoot. A mistake can be very unforgiving always good to be cautious.
 
It's chambered for 556 but marked for 223 in order meet sporting purpose and not be considered a weapon of war. Fire away.

They are the same parts and come from the same tooling.
 
Bartok5 said:
Well, thank goodness for that! I will take your continued pulse as a positive endorsement for 5.56mm through the MR 223, albeit with due regard for signs of overpressure as advised by Redshooter...
Click to expand...

It's chambering is very close to 556 milspec, it will be fine and in fact will shoot 556 better than 223.
 
Same stuff different Headstamp.

Black Hills .223 Rem
77 Gr. Sierra MatchKing

Velocity: 2750 FPS

Energy: 1293 Ft. Lbs.


Black Hills .5.56 NATO
77 Gr. TMK

Velocity: 2750 FPS

Energy: 1293 Ft. Lbs.
 
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