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So I haven’t seen but one post about someone cutting their mr556 down to 11.5”. I decided to take it upon myself to do it and report back to y’all what I find after I use it in a class this month. Since cutting it this past weekend, I’ve put about 100 rounds through it just to make sure it functioned properly. I welded the vent hole and am using the hk spring and buffer, nothing else. I’ll update this post at the end of the month after the class.

(Yes yes I know it’s on a Noveske lower. Hang me if you must, purists)
 

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So I haven’t seen but one post about someone cutting their mr556 down to 11.5”. I decided to take it upon myself to do it and report back to y’all what I find after I use it in a class this month. Since cutting it this past weekend, I’ve put about 100 rounds through it just to make sure it functioned properly. I welded the vent hole and am using the hk spring and buffer, nothing else. I’ll update this post at the end of the month after the class.

(Yes yes I know it’s on a Noveske lower. Hang me if you must, purists)
Too late but I would have read this before cutting your barrel seems like you lose accuracy.
https://www.hkpro.com/forum/hk416-hk417-hq/158827-don-t-cut-your-mr556-mr762-barrels.html
 

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Swiss_seth was the first I saw to cut to 11.5". Jayson Cotter (before he became PNG) did it; pretty sure the bleed-off was welded up.

Not gonna lie, the added height of the HK upper and the taller Unity mount does look a little odd.
 

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Too late but I would have read this before cutting your barrel seems like you lose accuracy.
https://www.hkpro.com/forum/hk416-hk417-hq/158827-don-t-cut-your-mr556-mr762-barrels.html
Pretty much the history agreed with Jon's post:
FN also does this with the SCAR. I know over a dozen of people personally who bought SCAR-16S rifles and cut them down with no appreciable loss in accuracy, knowing beforehand that this was a design feature of the SCAR barrel. I know 4 people whose MR556 barrels have been chopped as well with no real loss. Maybe if we bench rested them with a high magnification scope and match ammo there might be a slight fall...maybe..., but not enough to make a difference or notice in any other type of shooting. I wouldn't sweat it too much.

ETA: just got off phone with Larry Vickers about this...when asked if it would make a measurable difference to cut it down, assuming it was done properly/professionally with no workmanship issues at the crown or with the gas system, "My guess is no, it won't matter"

It was also said that HK centers the gas port for every 416 in the lands...that's incorrect. And because of some of G3K's old posts, there are a lot of folks that think every 416 will be sub-moa forever. They aren't all winners either in that respect either.

Cut it short if you want, gas it right, and be happy.
 

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This thread is relevant to my interests.

My next project is a 416/mr556a1 "other". Due to a quirk in our state law firearms between 26" and 30" and no stock are classified as firearms not a pistol. They don't have to be registered.
 
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Discussion Starter #13
Swiss_seth was the first I saw to cut to 11.5". Jayson Cotter (before he became PNG) did it; pretty sure the bleed-off was welded up.

Not gonna lie, the added height of the HK upper and the taller Unity mount does look a little odd.
yeah it looks tall, but it really does the job well for what I use it for. I enjoy the height due to my egg head haha
 

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yeah it looks tall, but it really does the job well for what I use it for. I enjoy the height due to my egg head haha
I ran a Micro T1 in a Larue mount on top of a 1/2" KAC riser (so magnifier or PVS14 could be mounted behind) for a while and people thought I was nuts. Dudes on LF were like "OMG...your holds are gonna be out of whack". Then the KAC mount came out and taller than 1.93" became a thing....LOL.

I don't run an RDS as primary any more. An RMR on top of the Spuhr gets the same job done for passive aiming.
 

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Too late but I would have read this before cutting your barrel seems like you lose accuracy.
https://www.hkpro.com/forum/hk416-hk417-hq/158827-don-t-cut-your-mr556-mr762-barrels.html
And multiple pin gauge tests of both MR556 and 416 barrels have proven all of that to be a myth.

Actual taper appears to be in the first inch to inch and a half of the bore and normalizes after that to the muzzle (which makes the use of standard GI issue throat erosion gauges a no-go). There was a slight constriction in the bore right around where the gas block pin holes were drilled, but even they they still let the gauge pass with slight pressure.
 

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And multiple pin gauge tests of both MR556 and 416 barrels have proven all of that to be a myth.

Actual taper appears to be in the first inch to inch and a half of the bore and normalizes after that to the muzzle (which makes the use of standard GI issue throat erosion gauges a no-go). There was a slight constriction in the bore right around where the gas block pin holes were drilled, but even they they still let the gauge pass with slight pressure.
That's what I alway wondered about how the taper was executed. My understanding was that the bore was smaller than usual at the muzzle.
 

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And multiple pin gauge tests of both MR556 and 416 barrels have proven all of that to be a myth.

Actual taper appears to be in the first inch to inch and a half of the bore and normalizes after that to the muzzle (which makes the use of standard GI issue throat erosion gauges a no-go). There was a slight constriction in the bore right around where the gas block pin holes were drilled, but even they they still let the gauge pass with slight pressure.
Do you have a link to these tests? I'm not doubting you. I would like have my mr556 cut down but don't want to lose any accuracy. The rifle is like a frigging laser.
 
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