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Discussion Starter #1
Everyone,

I have mostly been a lurker out here on the forum, but I have got one of my MR556's with Jayson at IGF.

I am having him do the following to it...

- cut it down to 14.5" and pin an AAC Blackout.
- reprofile to around 0.72 under hand guards and 0.68 in front of gas block
- Nitrocarburize/melonite barrel and gas block

I have a long hand guard (11") for this rifle, and cannot wait to get it back from him. I will let everybody know how this turns out. I definitely want to do something about the trigger on the MR also... I have two other rifles that having melonited barrels. They are the easiest to clean barrels I have ever seen. Very little copper every in the bore and comes out very easy. I will let everyone know how this turns out. I will most likely mod my other MR556 if this turns out well. I would like to do a 10.4", but debating on whether I want to deal with the SBR stuff.

It's really nice to see products and people modding this rifle. The non-chrome lined barrel and thick contour is a blessing in disguise sort of :). I just kinda gives you a blank slate to work with.


Brandon
 

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I would be hesitant in lopping off 6" of barrel due to the swage in the bore. The swage in an HK barrel is based on barrel length and no one has produced concrete evidence on the effects of such.

I have measured the muzzle bore on a factory 10.4". I'd be curious to know the I.D. at the lands of an MR555 barrel that has been cut to 10.4"
 

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You'll definitely like it. Your reprofile specs are what I had my MR barrel thinned too. You will have a very noticeable reduction in weight and it balances/handles much better (no longer so front heavy). The longer hand guard is also nice.
 

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I saw a definite improvement in accuracy on my rifle from when it was 16.5 compared to 14.5.

At 16.5 (pre-fat camp) the best I could do was 1 and 1/4 inch at 100, after the cut, re-profile, hand lap and nitride, I did a 9/16 inch group at 100.

Now, I CAN NOT attribute this to the barrel length though. The fact that the gun was brand new when I fired it at 16.5 inches and hadn't even thought about being broken in during the 60 rounds that I put through it initially, and the fact that I hand lapped the barrel, cut it, re-crowned it and then had it nitrided could have made the difference either seperatly, or in conjunction.

The only way to truly tell would be to hand lap a 16.5 barrel, re-crown it exactly as I did to mine, and then have it nitrided and then compare by putting both guns in a bench rest and taking the human factor out of the equation and shooting for absolute accuracy under ideal conditions.
 

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Discussion Starter #8
I shot a few rounds with the MR556 when I first got it. I was shooting M855 with an ACOG and seeing around 2.5" groups at 100yds. I definitely want to see what it can do when I get it back. I am going to get some 77gr Black Hills to see what potential it may have with that.
 

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As Grumpy said, you have to remove the human (and environmental) factors. An MR556 is indeed capable of sub-MOA accuracy. So unless you are capable of producing that, then you probably won't experience any loss cutting the barrel down from 16.5" to 14.5".

If you ARE a sub-MOA shooter, then perhaps you will. As for a 10.4" cut-down?... I really would be curious to know the muzzle I.D. at the lands on a cut-down barrel.

FWIW, unofficial and unconfirmed (by me) reports from the field are that well-trained (and capable) shooters are holding 2-1/2" to 3" groups at 200 meters with factory 10.4" barrels on well-used HK416's.
 

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I also forgot to add that when I did my best accuracy results after the barrel was cut to 14.5, I used 75 grain Hornady TAP ammo (re-zero for "go-to" ammunition. My original shooting pre-cut was with 55 grain federal m193.

Or something like that. I might be messing up my timeline too.
 

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I also forgot to add that when I did my best accuracy results after the barrel was cut to 14.5, I used 75 grain Hornady TAP ammo (re-zero for "go-to" ammunition. My original shooting pre-cut was with 55 grain federal m193.

Or something like that. I might be messing up my timeline too.
I'm guessing that has more to do with your accuracy than anything else
 

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I'm guessing that has more to do with your accuracy than anything else
Perhaps.

I just went back and refreshed my memory (frankly because I have a **** memory) and I got the original 1 and 1/4 inch group AFTER I finished the final assembly.

Because of your request, I later did the "accuracy" test that didn't turn out so accurate with the magnified scope that I had on hand, and didn't punch out the final 7 shot 9/16ths inch group until I gave up on trying to get a decent group with the magnified scope and had switched back to the aimpoint and magnifier for re-zero with my loadout ammo which is the 75 grain TAP.

To be honest, I think you're probably right. I don't consider myself to be the best shooter in the world by any stretch of the imagination and if I can pull a 9/16" group out of this rifle, I would think that there are millions of shooters out there better then me that could halve that group easily.

Or, the more likely answer is that I just got lucky.
 

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I am interested in getting this done. Would like to have the barrel cut down (width & length), recrowned, finished. Who does it and how much? Weight of the MR has kept me from getting one so far.
 

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Jayson at IGF is your best bet for barrel work.
 

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Marvin Pitts of Nefarious Arms does exceptional work.
 
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