The MR barrels are heavier profile and are not chrome lined.
Is there a difference between the barrels of a MR556 and MR556A1 and the 416? Is it material, rifling, ???
Lifetime NRA Member
The MR barrels are heavier profile and are not chrome lined.
and lets put a pin in this now.... we don't need yet another 416/MR barrel debate, chrome vs no chrome, etc.....
the materials are the same, the rifling is the same (cold hammer forged). the biggest difference is the MR barrels are not chrome lined, the 416 barrel being mil-spec'd (whatever the hell that means anymore???) are chrome lined.
Last edited by LCSO264; 10-20-2017 at 02:06 AM.
USP Tactical .45acp
HK 416 10.5" upper
HK45T (OD Green)
Thanks all. Sorry about not doing the search. Did not want to start a debate and don't really care chromed vs non chromed.
Here's a bit of non trolling that has bearing on this conversation.
It's been said that the MR556 barrel is exactly the same as a 416 barrel with the exception of the chrome lining. Without an optical emission spectroscopy test, we won't know this for sure. That being said, regarding their physical properties, I would have to say that the evidence comes down squarely on the side that says the barrels come from the exact same production line with the only difference being chrome added to the 416 barrels.
Pin gauge a barrel and you will find that a 416 will only let a .219" gauge drop fully through and the MR will allow a .220 gauge to pass.
The taper of the bore in a 416 barrel happens within the first 1.5-ish inches of the bore past the chamber before letting the .219 pin pass, and in the MR it is within the first 1.8-ish inches before letting the .220 pin pass.
I started with my M4 barrel erosion gauge as a base line in both the MR and the 416 barrel, then moved to the pin gauge set. I started with the .224 pin and worked down, with each successively smaller gauge going a little further into the bore until the .220 reaching full pass through on the MR and the .219 reaching full pass through on the 416.
If there is any further taper of the bore past the first 1.5 to 1.8 inches of the bore, it is so minimal that it cannot be indicated with pin gauges that only measure to thousandths.
It appears that the difference in which pin gauge they will allow to pass is caused simply due to the addition of chrome in the 416 barrel.
This also proves effectively once and for all that cutting any 416 or MR barrel from 16 to 14.5 or to 10.4 will have no effect on the taper of the bore at the muzzle.
Hey.....uhhhh I have a totally different experience. .220"- shouldn't be fitting in any 5.56 barrels. I use a .218"- pin in the muzzle, I have never gotten a .220"- to fit in a MR556 barrel. Edit---.220"- gets stuck in chamber
Do you have any idea on the chrome plating thickness? Also....I'm sure the mandrel is different on the chrome vs non chrome because the chrome will plate thicker on the corners of the rifling. If not compensated, it would be detrimental to precision.
Last edited by NoScoE30; 10-26-2017 at 06:45 AM.
I've two MR556 barrels, both with sub 2k round counts. One nitride, one not. The nitride one just went through a major cleaning and removal of all copper residue as it sat in the safe during most of my time in the middle east and developed the dreaded keyhole issue after 1300 rounds. (BTW, the complete cleaning process recovered the barrel to normal function as of today). Normally I just use turner stainless barrels so I don't burn up my HK barrels, but I decided to swap back to the nitride MR barrel after the aforementioned deep clean, and all gauging was done post deep clean, and pre-function test today.
The nitride barrel allows the .220 gauge to fit fully through. It does not just slide through. It does need slight finger pressure which is not only acceptable in gauging, but is required. TACOM has even defined "light finger pressure" as being up to 8.5 to 8.75 lbs in some cases (most notably in gauging headspace of the M4/M16). Relying on full unimpeded drop through does not give an actual good gauge, FYI.
That being said, I did NOT have to use 8.5lbs of pressure to get the .220" gauge to pass. Most likely less then 2lbs of pressure and that was mostly to over come the near perfect friction fit interference of the oil coating of the gauge. the .219" passed with less then half the pressure.
Now a double check of the non-nitride barrel with sub 2k round count and no deep clean, will not let the .220" gauge pass the bore taper, and the .219" makes it as far as 1.5" from the muzzle (on a 10.5" barrel) and the .218" passes fully. On a side note, this *may* indicate that there is a minor bit extra bore taper right up to just before the gas port, and if so, it would make sense that there should be no more taper taking place at the gas port and beyond. If this is true, the amount of taper from the 1.5 (416) to 1.75 (MR556) out to the gas port is measured in ten thousandths of an inch worth of constriction.
I chalk the discrepancy between the fully cleaned barrel and the fouled barrel up to the copper build up.
This is the result, I believe) of HK setting the bore size to accept chrome buildup without imposing on the bore diameter so much as to cause excessive bullet compression and increase pressure, and then taking barrels from the exact same manufacturing line and using them in MR556s' without adding chrome.To be honest, given the difference of pin gauges that pass, i'd guess it's a few thousandths thick at most. Given the taper of the bore, I'd venture a guess that it wears at the throat much less then a standard barrel which is where it matters the most. Most barrel accuracy starts at the throat. Yes, headspace has something to do with it and bore wear at the muzzle also effects it for sure, but throat erosion is the biggest killer of accuracy assuming there are no bore defects, blown rifling, pitting, etc.. It seems counterintuitive that having a 1.5" taper from the chamber would aid in accuracy as this allows an HK barrel to swallow a USGI throat erosion gauge well past depot reject standards, but at the same time it will *almost*, but not quite take an M240 throat erosion gauge past the same reject line. This obviously means that the gauge for an M249 is larger then an M4 gauge and the M249 isn't expected to have the same accuracy (beaten zone and whatnot). It also would seem that a slight taper that still has rifling allows the bullet to center correctly, thusly aiding in accuracy, whereas free bore with zero rifling which would cause problems.Do you have any idea on the chrome plating thickness? Also....I'm sure the mandrel is different on the chrome vs non chrome because the chrome will plate thicker on the corners of the rifling. If not compensated, it would be detrimental to precision.
All of that being said, I do believe that HK uses the same barrels and simply doesn't chrome line the MR barrels, which *might* be part of the reason that some folks seem to have issues getting theirs to actually shoot sub MOA.
One thing I did notice in the newly cleaned and copper free nitride bore is that the .220 and .219 pin gauges would need that slight pressure to get through the first part of the bore and then would drop through another part right up to the gas block and then require the slight pressure again. As if there were a slight expansions chamber for a couple of inches.
As I know that nitriding will not do that to a barrel, nor will 1.3k rounds, and no, I haven't had a squib round shot out either, the cynical side of me says that HK is taking their 416 reject barrel blanks and sending them to the MR556 line. Do I know this for true? of course not. But it does seem rather strange. Of course when this same barrel was 14.5" I had it easily shooting sub 3/4MOA, and now that it's 10.5 (yes, cutting a nitride barrel is not the easiest thing to do) it does about 1 to 1.5MOA-ish. Nothing to complain about.
Lets start with my sample set.
20 "turner" barrels
10 "turner" barrel ends (probably used to be attached to your turner barrels)
14 MR556 barrel ends
1 MR556 upper/barrel
NONE of them fit a .220"- pin, not with 8.75lbs. I could probably broach the rifling out if I rammed the .220"- pin.
Its clear that you are an experienced HK armorer, but you should probably check and calibrate all of your inspection equipment. Also, please do not force gauge pins.
Last edited by NoScoE30; 10-31-2017 at 04:39 AM.