Is your semi shooting like shit? May want to try this

[TheGerman]

I had a thread a while ago about how a HCS built Mk12Mod1 with the contract Douglas barrel, Ops Inc suppressor and everything on it being 100% the real deal would just not reliably shoot worth a shit. I tried every ammo possible, tried to load different bullets, powders, primers, everything...hell, I was to the point of thinking I needed to do a special accuracy dance before shooting it. Thread is here: https://www.snipershide.com/shootin.../6466966-mk12mod1-accuracy-problems-questions

It would group, and then the very next group of the same round, it would shoot like a fucking shotgun or it would put 3-4 rounds together with 1 or 2 rounds 2-4 inches in random directions. It was like something was loose but I had already checked the barrel, the rings, the scope and everything else. I cleaned it, didn't clean it, cleaned it some more, cleaned out copper, let it get super dirty, specifically didn't clean out copper, cleaned after every 20th shot and I just went crazy.

So between me, and 2 other SH'ers, both with Mk12s that they had some small degree of issue with at some point, we started to really trouble shoot things as I was at my wits end. I even had one load 50 of his 'go to' rounds for the Douglas barrel and send them to me for free. After a bunch of texts and figuring things out, I did the following:

- Changed the bolt out for a brand new bolt even though the current bolt only had a little more than 1k rounds on it. When I removed it, it was in 100% working condition but already had a circular etch from the primer/primer pocket that could be felt with a paper clip. This is from shooting full spec loads that basically flatten primers and is on the upper limits for the chamber.

- Unbolted and re-tightened the KAC gas block to exact 25 in/lb with a Borka driver to make sure they were even. Initially I had a little bit of gas coming out onto the top of the barrel which left a black film. While this isn't an accuracy issue, one of the 2 bolts in the block wasn't loose, but it was significantly less torqued than the other.

- Played with the hand torque of the suppressor. Initially I hand tightened and then tightened it some more. This time I made another witness mark that was right at 'hand tight' and kept it there as well as made sure via the witness mark that it wouldn't move/unscrew under recoil.

Went out yesterday with the same range of loads I've shot before. Almost immediately noticed a difference as there were 2 flyers the entire day and managed to shoot 4, 5 shot groups that were <.800 in a row while I was in/working around a node. Normally I would have shot maybe a good group with 1 flyer and then shot another group that would have looked like I was using buckshot.

The lone flyer can now probably be explained (one of the SH'ers had this issue) by needing a taper crimp on the round as this is what fixed his lone flyer issue.

But if you have a semi and it shoots like shit, you've checked your rings, scope and barrel and can't figure out WTF is going on, give your bolt and gas block a look as they may be the problem.

 

[redneckbmxer24]

I always put a dab of blue loctite on the gas block screws, it will keep them from loosening. The blow by from between the gas block and barrel is normal as they're two separate parts made to a spec and no gaskets or anything used.

As you mentioned a crimp will help with flyers, you will always have some though. The Lee crimp die solves it and works great as does running a bushing sizer to set about .004" neck tension. If you haven't crimped before, make sure you drop down a grain and work back up checking for pressure, same goes for higher neck tension. If you're running a higher pressure load it can put you over the edge.

 

[Not_A_Llama]

I've found that applying a little loctite around the gas port helps with initial accuracy before carbon has a chance to seal up the interface. It's a gasket type of situation.

OP, if you were to guess, which of the variables you changed would you say made the biggest difference?

 

[redneckbmxer24]

I've found that applying a little loctite around the gas port helps with initial accuracy before carbon has a chance to seal up the interface. It's a gasket type of situation.

Wow this is actually a great solution, I've never heard of anyone else doing this or thought of it. I use loctite in between other machined surfaces frequently mostly to prevent rust and it always sets up nice and hard. I'm going to start doing this and letting it set up. Thanks for the heads up.

 

[TheGerman]

I've found that applying a little loctite around the gas port helps with initial accuracy before carbon has a chance to seal up the interface. It's a gasket type of situation.

OP, if you were to guess, which of the variables you changed would you say made the biggest difference?

The only 'scientifical error' I made was that I changed all 3 things at one time. I knew this ahead of time because I'm after a fix and results and not on some scientific expedition. Once it actually did change things, I got curious and messed with the suppressor tightness - saw zero change, so I'm doubting its that.

If I had to guess, its mostly the gas block. I am betting that since the AR gas block is on the barrel, and I'm shooting very high pressure rounds (then again all rounds have a lot of pressure) that the loose gas block bolt was the main culprit in that it would move ever so slightly under recoil/gas being blown into it and basically disturb the barrel. The only real thing that makes me debate this is the question of why does it happen randomly instead of every round and I don't know the answer to that.

I'm also curious if the etched bolt face would sometimes cause the cartridge to sit ever so differently, mocking somewhat of what you'd get with a lot of runout on a bullet, and that had a a part in this.

Additionally, some of the big flyers may be due to recoil as it may be causing setback and/or movement on some of the rounds in the magazine. I still had 2 WTF flyers at the beginning but cut them down by 95% basically with these changes. The other SH member with the Mk12 I've been talking to mentioned he had just that issue and it was resolved by taper crimping the rounds. I've ordered a 5.56 taper crimp and plan to use it for the next batch.

 

[-=boone=-]

Glad to see everything has worked out.

 

[MSTN]

Please tell us you're NOT using ARMS #22 rings .....

 

[blcouch]

Please tell us you're NOT using ARMS #22 rings .....

Are they really that bad? I guess I need to do some bench testing when I get off the boat. Mine has had them since 05. Of course, I just shot the thing and never went for bench rest grouping. It'll be a good excuse for finishing the shooting platform I started before I left.


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[FatBoy]

Are they really that bad? ...

when we were building my first mk12 mod0 I was assembling parts and my buddy (and builder) recommended against them. They pulled them off their SF team guns and purchased carded Badger 20MOA Risers and rings. Worked well enough for them, and when the NXS 24mm scopes started coming in the riser could be deleted as it cleared the PEQ rail where the objective of the M3s didn't.

I won't (can't) say they are bad rings, but anything that loosen eventually will. Doubtful many of us will put it through the abuse it would take though.

 

[MSTN]

Are they really that bad? I guess I need to do some bench testing when I get off the boat. Mine has had them since 05. Of course, I just shot the thing and never went for bench rest grouping. It'll be a good excuse for finishing the shooting platform I started before I left.


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In my experience, after a certain number of on-off cycles with the lever, the ARMS throw lever mechanism tend to lose its tension. When this happens, the mount is able to slide in its rail slot under recoil.

 

[blcouch]

In my experience, after a certain number of on-off cycles with the lever, the ARMS throw lever mechanism tend to lose its tension. When this happens, the mount is able to slide in its rail slot under recoil.

Understood. I don't take mine off very often. Mostly during maintenance/paint stripping. I'll leave them be from now on.


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[MSTN]

Understood. I don't take mine off very often. Mostly during maintenance/paint stripping. I'll leave them be from now on.


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Same here. I've got an Elcan Specter DR with a dual ARMS throw lever base that has NEVER been removed from its host weapon.

 

[longshot2000]

I've found that applying a little loctite around the gas port helps with initial accuracy before carbon has a chance to seal up the interface. It's a gasket type of situation.

OP, if you were to guess, which of the variables you changed would you say made the biggest difference?

to be clear, are you saying on the gas port shoulder, so the gas block seals against the barrel, or into the gas port hole?

 

[JMcBurn]

The only 'scientifical error' I made was that I changed all 3 things at one time. I knew this ahead of time because I'm after a fix and results and not on some scientific expedition. Once it actually did change things, I got curious and messed with the suppressor tightness - saw zero change, so I'm doubting its that.

If I had to guess, its mostly the gas block. I am betting that since the AR gas block is on the barrel, and I'm shooting very high pressure rounds (then again all rounds have a lot of pressure) that the loose gas block bolt was the main culprit in that it would move ever so slightly under recoil/gas being blown into it and basically disturb the barrel. The only real thing that makes me debate this is the question of why does it happen randomly instead of every round and I don't know the answer to that.

I'm also curious if the etched bolt face would sometimes cause the cartridge to sit ever so differently, mocking somewhat of what you'd get with a lot of runout on a bullet, and that had a a part in this.

Additionally, some of the big flyers may be due to recoil as it may be causing setback and/or movement on some of the rounds in the magazine. I still had 2 WTF flyers at the beginning but cut them down by 95% basically with these changes. The other SH member with the Mk12 I've been talking to mentioned he had just that issue and it was resolved by taper crimping the rounds. I've ordered a 5.56 taper crimp and plan to use it for the next batch.

I am having the same weird flyers. I get 2-3 good shots out of 5 the rest are scattered. But I have changed the gas block to a clamp on and it still does it.

I think I am gonna try changing out the bcg and see if that fixes it.

 

[BurnOut]

I can believe this, as my own experience (sample size of one!) with getting/setting an adjustable gas block was that prior to the AGB, the rifle would shoot a particular off-the-shelf load (Fiocchi 50 gr V-Max in .223 Rem) at about 2-3 MOA. During the tuning of the AGB, as long as it was under-gassed (not locking the bolt back on an empty mag), it shot great... perhaps .75 MOA or so ("great" being relative; gun is an RRA 18" Varmint). Fortunately, it has maintained that accuracy even after getting the AGB properly set*.

I said all of that to say this... I can absolutely believe that there is accuracy to be had (or lost) in the gas system of an AR platform.




* I should note that the standard gas block tuning procedure of starting at full closed, then opening one notch at a time until it locks back on an empty mag, then adding two more clicks to account for weak loads worked fine, until I installed the suppressor. With the suppressor in place, it was over-gassed. Fortunately, there is *one* setting on the AGB that will allow the bolt to lock back on an empty mag either with or without the can, and sub-MOA accuracy is maintained.

 

[JMcBurn]

I can believe this, as my own experience (sample size of one!) with getting/setting an adjustable gas block was that prior to the AGB, the rifle would shoot a particular off-the-shelf load (Fiocchi 50 gr V-Max in .223 Rem) at about 2-3 MOA. During the tuning of the AGB, as long as it was under-gassed (not locking the bolt back on an empty mag), it shot great... perhaps .75 MOA or so ("great" being relative; gun is an RRA 18" Varmint). Fortunately, it has maintained that accuracy even after getting the AGB properly set*.

I said all of that to say this... I can absolutely believe that there is accuracy to be had (or lost) in the gas system of an AR platform.




* I should note that the standard gas block tuning procedure of starting at full closed, then opening one notch at a time until it locks back on an empty mag, then adding two more clicks to account for weak loads worked fine, until I installed the suppressor. With the suppressor in place, it was over-gassed. Fortunately, there is *one* setting on the AGB that will allow the bolt to lock back on an empty mag either with or without the can, and sub-MOA accuracy is maintained.

I totally agree my buddy's carbine shot perfecta in the 1.2" range at 100yd, but we switched to a hotter load and it shot awful. We put a gas block on it and it went back to shooting 1.2".

 

[TheGerman]

I am having the same weird flyers. I get 2-3 good shots out of 5 the rest are scattered. But I have changed the gas block to a clamp on and it still does it.

I think I am gonna try changing out the bcg and see if that fixes it.

I've done alot of research on loading/shooting with the Mk12 as of late with the help of another SHider where we basically started with bouncing ideas off each other, trying different loads, troubleshooting and exchanging notes throughout the week via text.

For the guys asking about the rings, yes they are the ARMS rings. No I haven't had them come loose, but who knows what is actually going on under recoil. Seeing as I have the NF 2.5-10x24, the NF rings are still in spec and decided to just get rid of the ARMS rings just because. Maybe its another weird variable that has some sort of effect every now and then? Maybe its absolutely nothing.

Some things that I think have been proven (for us at least);

- There is absolutely no noticeable difference other than BC between the 77 Nosler, 77 SMK and 77TMK as far as interchangeability assuming everything else is kept the same.
- Changing out the bolt face after etching it at around 1k rounds showed an immediate reduction in uncalled flyers
- Tightening the gas block to an even 25 in/lb on both screws (KAC block) showed an immediate reduction in uncalled flyers
- ???? ARMS rings may have something to do with flyers/inaccuracy ????? testing this
- The tightness of the suppressor has nothing to do with accuracy and does not disturb harmonics as far as being more/less tight; have only tightened by hand so any tighter than hand tight has not been tested/tried
- Seating depth may be a key to fine tuning out flyers with the MK12; however, instead of lengthening the round, initial testing shows seating the round .10 deeper than the standard COAL (or possibly even more) is increasing accuracy/decreasing group size and uncalled flyers; still testing this

 

[FUNCTIONAL]

Like you I had issues with my mk12 going from sub moa to holding 2" on a great day. I had rarely taken my scope off because there was no need. Well one day I got so frustrated I decided to clean the barrel back to brand new. One patch was particularly large and to push it through i put my hand on the rail just in front of one of the ARMS rings and wouldnt you know the damn think slid like a girl in a mud fight. Grabbed the scope and pushed it forward and back with ease. Not loose enough to rattle or shift under its own weight but a little bit of pressure and it moves.

As a test i threw duct tape on the clamp piece and it firmed it up enough to not move. Threw some rounds threw it and it was much much closer to its original accuracy. Got some shim stock and rolled pieces to fill the gaps behind the lugs and a small plate for the clamping piece and it was as it should be.

it was a gradual loss so i guess it just wore out. It is a HCS like yours and now i wonder if the receivers are just slightly under spec or at the smallest of the spec range or if the rings are that bad. In either case put some nail polish infron and in back of the ring and go shoot a bunch...see if it scrapes any off if you cant move it by hand.

 

[JMcBurn]

I've done alot of research on loading/shooting with the Mk12 as of late with the help of another SHider where we basically started with bouncing ideas off each other, trying different loads, troubleshooting and exchanging notes throughout the week via text.

For the guys asking about the rings, yes they are the ARMS rings. No I haven't had them come loose, but who knows what is actually going on under recoil. Seeing as I have the NF 2.5-10x24, the NF rings are still in spec and decided to just get rid of the ARMS rings just because. Maybe its another weird variable that has some sort of effect every now and then? Maybe its absolutely nothing.

Some things that I think have been proven (for us at least);

- There is absolutely no noticeable difference other than BC between the 77 Nosler, 77 SMK and 77TMK as far as interchangeability assuming everything else is kept the same.
- Changing out the bolt face after etching it at around 1k rounds showed an immediate reduction in uncalled flyers
- Tightening the gas block to an even 25 in/lb on both screws (KAC block) showed an immediate reduction in uncalled flyers
- ???? ARMS rings may have something to do with flyers/inaccuracy ????? testing this
- The tightness of the suppressor has nothing to do with accuracy and does not disturb harmonics as far as being more/less tight; have only tightened by hand so any tighter than hand tight has not been tested/tried
- Seating depth may be a key to fine tuning out flyers with the MK12; however, instead of lengthening the round, initial testing shows seating the round .10 deeper than the standard COAL (or possibly even more) is increasing accuracy/decreasing group size and uncalled flyers; still testing this

For me it was like all of a sudden rounds that used to shoot .6-1moa at 200yrds are now shooting 3" groups at 50 yards. I've swapped scopes, swapped mounts, tried scope/mount on known good rifle, swapped gas block.

All of this seemed to happen one day after I cleaned the rifle. It doesn't make any sense to me.

I think I am gonna do a heavy barrel clean and get all the carbon/copper fouling then shoot it again. Then swap BCGs and try again.

 

[TheGerman]

I'm primarily trying to figure out the flyers that I and alot of people seem to get. Where you put 3-4 rounds within an inch or less than then there's one round 4 inches to the right lol

In fine tuning in at least what I and some of those I'm trading ideas/testing with, the biggest thing I can remind people of is that for even the smaller 5.56 semi, one of the absolute things you need to keep an eye on is that while getting the rifle stock in your shoulder, that your shoulder is NOT tensed or pushing forward. The error this causes doesn't show up as prevalent on heavier bolt guns, but on something like the MK12 where its just barely bigger than a carbine, the multiple (yet small) impulses literally take that mistake and magnify it; its magnified even more so on larger semis. I've caught myself at times making this mistake because I've tried to get as much forward tension on the bipod to take any slack out of the system and then had to make a mental note NOT to for a while until I corrected me wanting to do so.

Pay attention to that when shooting next time as well and see if anything changes.

ETA- Forgot to add one more 'testing' result: Loading one more round in the magazine to where your last round shot isnt your last round loaded (i.e. no empty magazine) has no effect that I can tell on anything.