Mk12Mod1 accuracy problems/questions

[TheGerman]

Either my expectations are too high for the system or the 'journey' I've been on with this gun just seems to never end.

Full spec Mk12Mod1, Douglas contract barrel, Ops Inc suppressor.

I've done a metric ton of load development. Multiple powders, 2 bullets, an array of powder charges and I'm still having a problem keeping it under 1MOA during testing. Sometimes it'll put up a .7 group and then sometimes you shoot the load again and its 1.4 inches.

Nothing is loose. Nothing is moving. Nothing is broke. Everything has been cleaned, shot a while before cleaning again to see if it improved, cleaned again, etc. All brass looks fine anytime I shoot it, recoil is light/where it should be and I've shot a billion SA rounds downrange so its not me having to learn how to shoot a semi or anything like that. All of my extreme spread in groups is small and S/D is 95% of the time under 10fps.

I initially bought some red and blue box MK262 when I got the gun and the red grouped at right around an inch/1MOA from the get go. The blue was slightly worse with it teetering at right around 1 inch for 5 shot groups.

My first question is, for a Mk12 - what is the actual accuracy expectation? Is keeping it at/right under 1 inch/1MOA good to go and forget about trying to make it pound out .4-.5 inch groups like my MRAD?

Secondly, the gun seems to be VERY finicky with nodes. When you find one..you really find it because otherwise it likes to really open some of the groups in 'bad' nodes up. I think part of the challenge here is that the good nodes seem to be a very small window. I've had the best luck with a 77g TMK and RL15 as well as 8028 XBR (tested the XBR today and had everything from horrible to showing promise) - one of the things I saw online with the 77g is while normal mag length COAL is 2.260, a lot of people had mentioned they loaded the 77 to 2.245. Is there a reason for this? I've never heard of a further jump helping, but maybe there is some voodoo here, or maybe some mags are shorter and my NHMTG mags can run the 2.260?

I let the barrel cool a bit between strings like most do. I notice that the barrel will cool rather quickly yet the suppressor will stay much hotter - does the heat on the suppressor matter other than it giving off a mirage? Does the suppressor being hot/cool do anything as far as effect the round passing through it? I would think it doesn't as its not actually touching, but figured I'd ask.

Anyone have any semi auto loading/testing ideas? Or am I simply wanting too much out of this?

 

[GH41]

I think you just got what you got. If you bought 10 Mk12 uppers a couple of them might do better than the others and a couple might do worse. I'd say yours is in the average group.

 

[MtnCreek]

I get a little better than moa with prepped LC brass, 77 smk and imr8208 in a HCS upper. 75 gr hornady opens up a little, but not much. I have a mod 0 clone with woa spr barrel that shoots a little better.

 

[Bakwa]

If I recall, in the Marine Corps the DM and SS guys that carried MK12's got right at 1MOA-1.25MOA wit their heavier issued match ammo. It sounds like you're on PAR.

 

[demolitionman]

Have you tried changing brass? I went through a similar experience with my dmr type and although it makes little sense to me, my last ditch effort for accuracy was to try different brass. I did everything else i possibly could. Going from fully prepped LC to fully prepped out of the bag Winchester brought my groups @ 100 from 1"+ to 3/4" no problem. For some reason every single load i tried shot better in Win brass.
24g Varget 77smk 1/7 twist

 

[TheGerman]

Have you tried changing brass? I went through a similar experience with my dmr type and although it makes little sense to me, my last ditch effort for accuracy was to try different brass. I did everything else i possibly could. Going from fully prepped LC to fully prepped out of the bag Winchester brought my groups @ 100 from 1"+ to 3/4" no problem. For some reason every single load i tried shot better in Win brass.
24g Varget 77smk 1/7 twist

I've used virgin Remington, reloaded IMI (from Mk262) and now the NATO headstamped virgin Federal.

But good/bad news, I emailed HCS and it seems from CRANE the accuracy requirement is 1 MOA. He mentioned some do get a little better and it seems I got a gun that shoots in the average/qual spec range. So looks like I just have what I have.

 

[WarbirdWeaponry]

The MK12 has a NATO chamber correct? One advantage to a clone barrel is getting a Wylde or match chamber, tighter freebore dia.

 

[Redmanss]

What optic and how do you have it mounted, along with what type buttstock are you running and how good of cheek weld do you get? The NF and Leupold optics that were typically issued were fixed parallax at 300m, and getting consistent stock weld with 1.5" rings and a standard A2 or SOPMOD style buttstock is far from easy, so it may simply be a parallax issue you're running into causing the groups to shrink and widen.

 

[Mike_Honcho]

Regarding group size - are they tight w/ a flyer or more uniformly dispersed?

Brass - how much prep did you put into the Win cases? My experience with Win Cases is that the weights are less consistent than LC, the necks are dinged and out of round, and in general they require a full prep - including drilling out and then chamfering each flash hole, and at minimum using the expander ball on the mouth. Regarding the other brass - when was the other brass annealed? (I have read from multiple sources that brittle brass can be an issue with groups as well).

Regarding potential accuracy - IMHO most of the claims on the net regarding the every day / every condition accuracy of anything leads to false expectations. IMHO a quality SA of any caliber should be expected to hold 3/4 MOA and if you get better than that, good on you.

At 700 that 1/4 MOA (that folks think they will overcome with a magic load or the special way they faced the upper or froze or heated or held a voodoo ceremony) means less than 2". Frankly, that doesn't keep anyone out of the COM A zone.

Wind > Load - IMHO

 

[TheGerman]

What optic and how do you have it mounted, along with what type buttstock are you running and how good of cheek weld do you get? The NF and Leupold optics that were typically issued were fixed parallax at 300m, and getting consistent stock weld with 1.5" rings and a standard A2 or SOPMOD style buttstock is far from easy, so it may simply be a parallax issue you're running into causing the groups to shrink and widen.

NF 2.5-10x24, ARMS rings and changed the SOPMOD out for a Magpul ACS stock because of the cheek weld issue you mentioned.

From prone the cheek weld is fine and holds through recoil. At first I started getting things in my head like something was loose, or I wasn't holding the rifle/had bad body position but outside a few odd times where I just don't line up 100% correctly, I pull the trigger, it recoils and the reticle is right by my initial POI as well as no scope 'edging' or shadowing.

 

[TheGerman]

Regarding group size - are they tight w/ a flyer or more uniformly dispersed?

Brass - how much prep did you put into the Win cases? My experience with Win Cases is that the weights are less consistent than LC, the necks are dinged and out of round, and in general they require a full prep - including drilling out and then chamfering each flash hole, and at minimum using the expander ball on the mouth. Regarding the other brass - when was the other brass annealed? (I have read from multiple sources that brittle brass can be an issue with groups as well).

Regarding potential accuracy - IMHO most of the claims on the net regarding the every day / every condition accuracy of anything leads to false expectations. IMHO a quality SA of any caliber should be expected to hold 3/4 MOA and if you get better than that, good on you.

At 700 that 1/4 MOA (that folks think they will overcome with a magic load or the special way they faced the upper or froze or heated or held a voodoo ceremony) means less than 2". Frankly, that doesn't keep anyone out of the COM A zone.

Wind > Load - IMHO

Almost all are just a larger dispersed 5 shot group. I've had a few where 3 are literally on top of each other, then the other 2 are either right next to each other but almost an inch away -or- the group is simply spread out.

Like I said, when this gun/barrel is not in a good node, it shows you right away and makes it obvious. When in what I think is a node, I can hold +/- an inch with some groups then being a bit larger all of a sudden.

For the brass, I've used Remington, IMI and NATO stamped Federal. All 3 got the full prep outside of turning the necks, but I do drill out the flash holes, even out the primer pockets, FL size with Redding bushing die (specific bushing for each bullet/case combo). I'm not thinking its the brass though as my ES for groups is low, and my S/D is 90% under 10fps. If it was a brass issue, wouldn't that be all over the place?

Only other thing I can think of but I doubt they matter:

- the suppressor being hot (don't think this effects anything)
- the gas block seems to leak/have a bit of gas blown out of it as on the FDE cerakote I can see where its getting dirty around that area but its fairly minor and I cant see how that would matter on anything outside of function

 

[Redmanss]

Stretch its legs in a light wind day, see what it will do at 300m, just to see what downrange effects are on your groups. Otherwise, keep in mind you're also running a 10x optic and while they're not bad for group shooting at 100m, they're certainly not a >17x type mag optic for fine tuning your hold. More than likely, it's just a finicky barrel but still not sub-par. My own built by Monty at Centurion does best with red box MK262 from BH, and that's about .7-ish moa on my good days.

 

[Pusher591]

Had a 18" Noveske that shot 1-1.50" groups at a hundred. Didn't matter what match ammo or shooter was used but 300-800 yards shot 1/2 Moa or less. Beat all I've ever seen.

 

[Primus]

Who built the gun? If you aren't getting sub MOA with a quality barrel (Lija, WOA, CLE, Krieger) then either the gun was put together by someone who didn't know what they are doing, you got a bad barrel or you can't shoot for shit. EVERY single MK12 I have built over the years has shot sub moa (69gr FGMM, 75GR Black Hills & 77GR Black Hills). Hell even the noveske based MK12 builds I have done over the years have been shooters.

If you are using Arms #22's, trash those pieces of shit and get a quality once piece mount. Make sure the brake is timed correctly, and play with the torque values on the barrel nut.

 

[Blazin]

I built a DMR using a Centurion Mk12 barrel. With the right load & shooter it's a 0.5 MOA gun, and any decent quality ammo shoots 1 MOA or better, it's an impressive barrel. The chamber on this gun is the tightest I've ever seen on an AR, but the throat is longer than I'd like. I think you should look at the basics again: scope securely mounted, good known scope, gas tube interference with bolt carrier, quality bolt (I use a Young Manu BCG), good trigger, solid bench or rest with shooting groups.

 

[blbennett1288]

HCS built my MK12MOD1. I consistently get ~1MOA. I am sure a lot of this has to do with me and not the rifle, but 1MOA is what is expected out of the MK12. The AR15.com MK12 thread might yield better results as it is one of the best threads I have encountered to date.

 

[MSTN]

In 2002, I bought one dozen SPR uppers (two Mod 0's and ten Mod 1's) from the two contractors that built the majority of these rifles for Crane, Vince Jiga (now deceased) and John Miller. We used all of the correct parts short of the BCG's. The Government guns of the era all had used M16A1 BCG's in them. We used commercial Colt bolts and Young Mfg bolt carriers.

The accuracy requirements for the Government guns were surprisingly low. It's like there was a war going on or something! Three shots into 1.25 MOA at 100 yards with Mk 262 was GTG. Only three of the uppers delivered came with test targets under MOA. Very disappointing.

The SPR utilizes a proprietary Crane-designed chamber, not a NATO chamber.

I've built a great number of precision AR' rigs in the intervening years, utilizing barrels from Douglas, Krieger, Lilja, Noveske, V 7, and Bartlein. No rifle will outshoot its barrel. While a GOOD Douglas will shoot with the absolute best of barrels, the better quality barrels simply give on average better results.

But, it's not always the barrel that causes an accuracy issue.

The biggest problem I've run into with SPR's is the 12th Model brake. For the longest time, there would be machining chips on the inside of the forward baffle that needed to be reamed out. But that was years ago resolved. Barrel collars not fully bonded to the barrel are another easy to miss problem. Lastly - and this is with any SS AR' barrel - the initial stage of gas port erosion - in the form of an overly large chunk displaced from the barrel forward of the gas port - can take a hundred rounds to blend in and go away. Accuracy suffers until then. The telltale clue is a bright streak of copper forward of the gas port all the way to the muzzle.

I'd also suggest getting rid of those ARMS #22 rings.

 

[bab029]

Lastly - and this is with any SS AR' barrel - the initial stage of gas port erosion - in the form of an overly large chunk displaced from the barrel forward of the gas port - can take a hundred rounds to blend in and go away. Accuracy suffers until then. The telltale clue is a bright streak of copper forward of the gas port all the way to the muzzle.

This is interesting. Machining marks from gas port drilling is something I have been pondering with regard to barrel break in. Perhaps a few boxes of hot 5.56 with a couple of cleanings thrown in is a good idea to smooth this area out. Certainly before any load development or despairing over poor accuracy is initiated. I'll be testing a ballistic advantage barrel from aero over the next few weeks, so I'll try to document what I do in the first hundred rounds or so.

 

[6172crew!]

I was getting 5/8" groups until I swapped scopes to the NF SFP 2.5-10X32, the parallax (or lack of adjustment) shows up when I shoot for groups. the vortex FFP PST was a better scope. Mine is a HCS Mod 0. I am thinking about buying a Mod 1 from centenarian arms, and placing the 2.5-8 loopy on the mod 0 and moving the NF to the Mod 1 but Im moving the problem over to a better platform.

 

[-=boone=-]

Two matching 20" "SPR" Douglas CLE match chambers. Barrels were bought years apart from each other. Both shoot sub MOA consistently from 70 RDFs to 77 TMKs.

You might make a call to Frank at Compass Lake Barrels.

If you would like to further discuss this via PM that's fine. Also I could manage to drop some of my different reloads in the mail for you.

 

[TheGerman]

Two matching 20" "SPR" Douglas CLE match chambers. Barrels were bought years apart from each other. Both shoot sub MOA consistently from 70 RDFs to 77 TMKs.

You might make a call to Frank at Compass Lake Barrels.

If you would like to further discuss this via PM that's fine. Also I could manage to drop some of my different reloads in the mail for you.

Is this directed to me?

If so you can probably just give me your load recipe; or IM me and I'll take the reloads.

Right now, the only 2 promising loads I've had that seem to find a node are 24.6-24.8 RL15 and 23.2-23.5 IMR8208.

The scope parallax may be something to look into as it is the spec 2.5-10x24 with no adjustment. I've been wanting to change out the ARMS rings for NF rings as I had initially had this built as close as possible to the real thing, down to the M16A1 lower. Then again, as stated, people have seen NF rings fairly commonly on the Mk12 so that may not be too far off.

I talked to the guys at HCS and they also mentioned what was said above, that the accuracy requirement was basically 1MOA, which, plus or minus at the end of the day is where I'm at. I was more curious of 'what SHOULD I be getting' and being realistic. I mean, my MRAD is pounding 5 shot sub .5MOA groups, but there are some people getting .75 or near MOA; doesn't mean their gun sucks. As long as I'm not the odd man out, and what was actually realistic is where I'm at, I'm not going to lose sleep over it especially for something considered a battle rifle.

However, if we can get this to shoot better, I'm not going to complain either.

 

[MtnCreek]

Any chance the old (assumption) lower is worn / loose?

 

[TheGerman]

Any chance the old (assumption) lower is worn / loose?

It's not a rattletrap but its got that little bit of give when locked up.

 

[blcouch]

If you are using Arms #22's, trash those pieces of shit and get a quality once piece mount. Make sure the brake is timed correctly, and play with the torque values on the barrel nut.

Mine must be defective. I've had them on my Mod1 since 2005 and they've been more than adequate over several thousand rounds.





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[Scotts556]

Not to try and piss on the party here. But it is a SPR, Not a sniper rifle. I love bug hole groups just like everyone else. But then again a MK12 is not a sniper rifle. So I would say 1 MOA Is doing pretty well.

Scott

 

[Primus]

Actually it is a sws, just in 5.56. When snipers take this as a primary on a SR/overwatch mission over a sr25, its a pretty good indicator.

M24 had a moa requirement of 1.3moa I believe.

 

[Primus]

Mine must be defective. I've had them on my Mod1 since 2005 and they've been more than adequate over several thousand rounds.





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Im sure there are guys out there with hesse/vulcans who think their guns are the shit too.....

 

[Forgetful Coyote]

Either my expectations are too high for the system or the 'journey' I've been on with this gun just seems to never end.

Full spec Mk12Mod1, Douglas contract barrel, Ops Inc suppressor.

I've done a metric ton of load development. Multiple powders, 2 bullets, an array of powder charges and I'm still having a problem keeping it under 1MOA during testing. Sometimes it'll put up a .7 group and then sometimes you shoot the load again and its 1.4 inches.

Nothing is loose. Nothing is moving. Nothing is broke. Everything has been cleaned, shot a while before cleaning again to see if it improved, cleaned again, etc. All brass looks fine anytime I shoot it, recoil is light/where it should be and I've shot a billion SA rounds downrange so its not me having to learn how to shoot a semi or anything like that. All of my extreme spread in groups is small and S/D is 95% of the time under 10fps.

I initially bought some red and blue box MK262 when I got the gun and the red grouped at right around an inch/1MOA from the get go. The blue was slightly worse with it teetering at right around 1 inch for 5 shot groups.

My first question is, for a Mk12 - what is the actual accuracy expectation? Is keeping it at/right under 1 inch/1MOA good to go and forget about trying to make it pound out .4-.5 inch groups like my MRAD?

Secondly, the gun seems to be VERY finicky with nodes. When you find one..you really find it because otherwise it likes to really open some of the groups in 'bad' nodes up. I think part of the challenge here is that the good nodes seem to be a very small window. I've had the best luck with a 77g TMK and RL15 as well as 8028 XBR (tested the XBR today and had everything from horrible to showing promise) - one of the things I saw online with the 77g is while normal mag length COAL is 2.260, a lot of people had mentioned they loaded the 77 to 2.245. Is there a reason for this? I've never heard of a further jump helping, but maybe there is some voodoo here, or maybe some mags are shorter and my NHMTG mags can run the 2.260?

I let the barrel cool a bit between strings like most do. I notice that the barrel will cool rather quickly yet the suppressor will stay much hotter - does the heat on the suppressor matter other than it giving off a mirage? Does the suppressor being hot/cool do anything as far as effect the round passing through it? I would think it doesn't as its not actually touching, but figured I'd ask.

Anyone have any semi auto loading/testing ideas? Or am I simply wanting too much out of this?

Say German, didnt you once do a HK G28 clone? Just curious, do you know how (im)possible is it to get hold of a true HK 416 upper? Or to otherwise build a DEVGRU style 416 clone? Sorry for going off topic

 

[TheGerman]

Say German, didnt you once do a HK G28 clone? Just curious, do you know how (im)possible is it to get hold of a true HK 416 upper? Or to otherwise build a DEVGRU style 416 clone? Sorry for going off topic

Wasn't me.

I tend to stay away from H&K (not that they make that hard to do!) since my extreme love/hate relationship with the G3A3 and being a tiny part in the feedback process to further the development of improvements to the A3/ZF variants which they listened to absolutely jack shit nothing about.