MK 12 Picture & Discussion Thread

Everyone I have talked to for the most part agrees that 8202XBR is the ticket for this style rifle. Have you experience any seating depth issues with the TMK?

The load I posted above is a mag length COAL of 2.260 and have never messed around with seating the bullet further in especially once I was getting 2675fps from the 16 inch barrel.

I messed with depth a ton on the Mod1 when I was trying to do practically anything to get it to group better over all of the component changes, and did see some positive changes in a few loadings when you decreased the depth by .10 and .20
 
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The load I posted above is a mag length COAL of 2.260 and have never messed around with seating the bullet further in especially once I was getting 2675fps from the 16 inch barrel.

I messed with depth a ton on the Mod1 when I was trying to do practically anything to get it to group better over all of the component changes, and did see some positive changes in a few loadings when you decreased the depth by .10 and .20

Are you using a bushing die, and do you crimp? I want to get away from the factory ammo and start loading for mine, but never have loaded for a semi and the neck tension thing seems a little contentious.
 
Are you using a bushing die, and do you crimp? I want to get away from the factory ammo and start loading for mine, but never have loaded for a semi and the neck tension thing seems a little contentious.

I use the Redding bushing die with the button pulled out and then finish the case with a TiN mandrel to get the neck tension I want for the specific brass/bullet combination. Make it smaller with the Redding bushing, slightly expand it with the TiN.

I don't crimp. Only thing that has ever done was screw up my S/D and ES numbers. With .002 tension and mag length loaded (or at least not jamming it into the lands, which for AR chambers on mag fed guns is basically impossible to do) you should be fine as far as the bullet staying where it needs to in the neck.
 
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Went to 575 today with ease. Wind was fun for a while then died off completely. IMI 77 Razor Core may be just a bit too spicy. If I calculated it right, it was hovering around 2,900 FPS and only took 12 MOA out to 575. Old numbers and charts were saying 15’ish.
 

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24-24.4gr of Varget or RL15 under a 77SMK (been taper crimping them lately) LC or Win case with 205 primer is a very accurate load to 600y. (I drop .3gr with win cases)

Not as hot as real deal 262. Around 12 moa to 600 depending on temp. Not sure what MV is, around 2800.

Off the shelf I was shocked how accurate the FC262 was. Not cheap but it shot half MOA at 500y. Most days I'm a 3/4moa shooter with a gas gun but a 3" singer was boring unless the wind picked up.

What length is your barrel? I have never seen anyone get anywhere close to that kind of speed on varget with those components. ~2600 is more the normal with 16-18" Even with more energy-dense powders like TAC and 8208, you are still at max 5.56 load data to get that kind of speed in a suppressed 18" with the SMKs.

So let's play this out- assuming a G7 BC of .193 and ~12 minutes to 600 yards with 2800 fps.... you're at 12,500ft above sea level?

Whatever it is, it seems to be working for you... if a 3" target at 500y with a .223 gas rifle is easy enough to be "boring," I would not change a thing.
 
Went to 575 today with ease. Wind was fun for a while then died off completely. IMI 77 Razor Core may be just a bit too spicy. If I calculated it right, it was hovering around 2,900 FPS and only took 12 MOA out to 575. Old numbers and charts were saying 15’ish.

Something is up...did it sit out in the sun for a while? It's also possible they are using a different projectile with a slightly better profile.

I can tell you this, with a .193 G7 Nosler CC (Litz AB data) running between 2695 at 35F and 2780 at 95F in the sun/hot gun I am 14.7 moa to 575 according to AB at 70F. I've trued it at 600.
 
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What length is your barrel? I have never seen anyone get anywhere close to that kind of speed on varget with those components. ~2600 is more the normal with 16-18" Even with more energy-dense powders like TAC and 8208, you are still at max 5.56 load data to get that kind of speed in a suppressed 18" with the SMKs.

So let's play this out- assuming a G7 BC of .193 and ~12 minutes to 600 yards with 2800 fps.... you're at 12,500ft above sea level?

Whatever it is, it seems to be working for you... if a 3" target at 500y with a .223 gas rifle is easy enough to be "boring," I would not change a thing.


the MV was a wild ass guess. I didn't even bother reverse data input to see because I can't go any hotter. I just compared my come up against what I normally see with my 6BR or 6.5x47s, which each take about 11.5-12moa to get to 600 at 2850.

Running it now, there is no way 12 moa is correct. maybe it was 17? I'll have to dig my book out to know for sure. Regardless, my memory of that come up is bullshit. The load is solid though, in a Wylde chambers 1:7, 18".

The barrel is a WOA SPR 1:7. After shooting it a buddy bought the same barrel for his build and it's the same deal. He has a variable Leupold (I think 3-10 firedot?) and my loads or BH 77s are super accurate at 500 and 600 if there is no wind. Once wind picks up, things are significantly more difficult. but that's on us.

edit: Just pulled the rifle out and it still has the come up from the last time I shot at 600. 17.25 moa up from a 100y zero. So, around 2700 IF my reversed numbers are correct.
 
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Something is up...did it sit out in the sun for a while? It's also possible they are using a different projectile with a slightly better profile.

I can tell you this, with a .193 G7 Nosler CC (Litz AB data) running between 2695 at 35F and 2780 at 95F in the sun/hot gun I am 14.7 moa to 575 according to AB at 70F. I've trued it at 600.

This is kind of why I asked. I shoot the TMK and with a 16" Holland I'm at 11MOA at 515 yards.
 
the MV was a wild ass guess. I didn't even bother reverse data input to see because I can't go any hotter. I just compared my come up against what I normally see with my 6BR or 6.5x47s, which each take about 11.5-12moa to get to 600 at 2850.

Running it now, there is no way 12 moa is correct. maybe it was 17? I'll have to dig my book out to know for sure. Regardless, my memory of that come up is bullshit. The load is solid though, in a Wylde chambers 1:7, 18".

The barrel is a WOA SPR 1:7. After shooting it a buddy bought the same barrel for his build and it's the same deal. He has a variable Leupold (I think 3-10 firedot?) and my loads or BH 77s are super accurate at 500 and 600 if there is no wind. Once wind picks up, things are significantly more difficult. but that's on us.

edit: Just pulled the rifle out and it still has the come up from the last time I shot at 600. 17.25 moa up from a 100y zero. So, around 2700 IF my reversed numbers are correct.

Sounds pretty close; velocity might be even lower...I never worked up Varget with that bullet but everyone I know who did was in the 2600 range with 24-24.5gr, so you might have a fast barrel.

Either way, sounds from your first post like that load is killing it whatever the speed...

IMG_1299.JPG
 
Sounds pretty close; velocity might be even lower...I never worked up Varget with that bullet but everyone I know who did was in the 2600 range with 24-24.5gr, so you might have a fast barrel.

Either way, sounds from your first post like that load is killing it whatever the speed...

View attachment 6938857

85°-95°
400AMSL
40-80% humidity most days

MV could be lower. I haven't done a tall target test with this 32mm NXS so its possible for sure and I didn't measure me exact scope above bore, but the come ups are repeatable so ehh. That's all that really matters.

The FC262 is flatter to 500 for sure. (so is BH77) and the most accurate ammo I have shot out of this rifle. I don't remember exactly how much flatter but IIRC maybe 2 MOA. It's what started me down this damn crimping path. I am trying different taper crimps with each powder to see if I can increase the pressure and get closer ti the FC262 MV. so far, all I've done us waste power and bullets. I think I'd need to change powders to get any more MV out if it.

If I didn't have 32# of Varget on the shelf I would shoot rl15 only. It seems to burn a little cleaner. I have around 600 rounds on it now with zero cleaning, mix if the two powders. I just coat the bolt and carrier with CLP and shoot. It's damn filthy, and I'll probably have to soak it to get it clean but I want to see how far it'll go. That can is super nice but man does it put some residue back in the receivers and mag.

edit: have you rebuilt your USGI 20 rounders? Mine are spent and double so I have switched to 20 round Pmags for now but I'd like to rebuild them. I'm not up to speed on what the best follower, etc us these days.
 
85°-95°
400AMSL
40-80% humidity most days

MV could be lower. I haven't done a tall target test with this 32mm NXS so its possible for sure and I didn't measure me exact scope above bore, but the come ups are repeatable so ehh. That's all that really matters.

The FC262 is flatter to 500 for sure. (so is BH77) and the most accurate ammo I have shot out of this rifle. I don't remember exactly how much flatter but IIRC maybe 2 MOA. It's what started me down this damn crimping path. I am trying different taper crimps with each powder to see if I can increase the pressure and get closer ti the FC262 MV. so far, all I've done us waste power and bullets. I think I'd need to change powders to get any more MV out if it.

If I didn't have 32# of Varget on the shelf I would shoot rl15 only. It seems to burn a little cleaner. I have around 600 rounds on it now with zero cleaning, mix if the two powders. I just coat the bolt and carrier with CLP and shoot. It's damn filthy, and I'll probably have to soak it to get it clean but I want to see how far it'll go. That can is super nice but man does it put some residue back in the receivers and mag.

edit: have you rebuilt your USGI 20 rounders? Mine are spent and double so I have switched to 20 round Pmags for now but I'd like to rebuild them. I'm not up to speed on what the best follower, etc us these days.

I have some rebuilt USGI 20’s that work pretty good. But I also bought some new Colt 20 rounders so I take them 9/10 trips.

On the rebuild, I think I ordered the Brownells kits and just kept the retro floorplate. It’s a basic plastic follower that replaces the old ones, and new spring at that point. I don’t think they’ve spent much time doing R&D on 20’s in years. Plus the straight feed doesn’t make the new fancy follower as necessary.
 
Something is up...did it sit out in the sun for a while? It's also possible they are using a different projectile with a slightly better profile.

I can tell you this, with a .193 G7 Nosler CC (Litz AB data) running between 2695 at 35F and 2780 at 95F in the sun/hot gun I am 14.7 moa to 575 according to AB at 70F. I've trued it at 600.

It was hotter than hell and no cover so ammo was baked. It was the same case of factory IMI 77 smk 5.56 I’ve been shooting a while now.
 
Great rifles so far.
Question on red dots..
The Burnett gen 1 offset Mount seems impossible to find.
I remember seeing a pic with a red dot mounted on top of the scope behind turrets.
Any currently available setup correct?
What red dot? Anything other than early doctor correct?
One last question. I have a kac ambi mag release, or of place?
Thanks
 
Great rifles so far.
Question on red dots..
The Burnett gen 1 offset Mount seems impossible to find.
I remember seeing a pic with a red dot mounted on top of the scope behind turrets.
Any currently available setup correct?
What red dot? Anything other than early doctor correct?
One last question. I have a kac ambi mag release, or of place?
Thanks

Most I’ve seen were the Dr. Red dot. Mostly on Mod 1’s on top of the TRRC ring cap. But here’s a later gen Mod 0 like mine with one.

For the Burkett mount, I think he’s in jail at the moment. Gen 1’s pop up but not very often. Could post a WTB add a few places.
 

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Great rifles so far.
Question on red dots..
The Burnett gen 1 offset Mount seems impossible to find.
I remember seeing a pic with a red dot mounted on top of the scope behind turrets.
Any currently available setup correct?
What red dot? Anything other than early doctor correct?
One last question. I have a kac ambi mag release, or of place?
Thanks

For the Mod1 (not sure if they did this for the Mod0), there is a mount that is the top half of the ring section for the Nightforce rings made by Wilcox. It is specific to the Insight MRDS or the Doctor footprint (which is what is correct anyways) and puts it low enough to not need a chin weld but high enough to where it will clear the elevation turret.

They are rare to find. Occasionally one will pop up on ebay but they will easily go for $400+. I tried contacting Wilcox about it and was told they have long been discontinued, which is weird because there were 1 or 2 on ebay in the last year new in the Wilcox wrapper with the correct tag on it and had a manufacture date within the last 6 months. Ended up finding mine by pure luck; if you don't want to try and get one, or spend a ton of money on $7 worth of metal, there are a few things out there that can get you close, but not 100% correct.

As for the Burkett mount, they are also now only found in the secondary market. I haden't seen them on a MK12 until I saw them on the Mod H; not sure if they were ever used on the 0/1. For the Holland, you can use the Burkett, or using a LaRue LT787 plus a T1 micro Aimpoint is also good to go; this is the setup I have.

The lowers were primarily all Colt or Hydramatic M16A1s with the low shelf profile. It is very unlikely that a KAC SR15 was ever used; but that is kind of the allure to the Mk12 as you keep seeing pictures of them in use, with random parts on them at times.
 
Some brief history. The original program was to develop the SPR; special purpose receiver. SOCOM wanted a upper to go with the 14.5” and 10.3” kits to really give the end user a wide range of environments for their M4’s. They were having some issues making the rifle gas and carbine extension work. Somewhere along the line a unit had sent Crane a ton of barely used M16A1’s to be de-milled. Crane asked if they could try them on the SPR project with a trigger upgrade. The special purpose receiver then became what we now know as the special purpose rifle.

So yes, if you wanna get into it hardcore a A1 profile is best. Or you know a transferable lol. I used a Nodak, PRI and Brownells have them to. Some guys have A2 80% or 80% A1’s marked and mill them out. No one is going to give you too much hell over the incorrect lower as long as it’s not some billet skull shit.
 
It was hotter than hell and no cover so ammo was baked. It was the same case of factory IMI 77 smk 5.56 I’ve been shooting a while now.

I totally believe it. I have not pulled any of the IMI Razor core to see what they use. It is probably a ball powder which tend to be a little more sensitive. Any powder through, even really stable stuff like Varget or H4350 starts to get squirrelly if left out in the sun on a hot day...remember it is also heating up even more sitting in the chamber.

I use a lot of TAC, which is what BH allegedly uses for their MK262 and is very stable for a ball powder... it will still vary close to 100fps going from overcast near freezing to 90F and baking in the sun.

8208 is really the best choice here in reloading this round for maintaining temp stability while getting the kind of speed and precision you want. None of the other stick powders give you the energy density you need to get to 2700+ in the MK12 barrel lengths without compressing or loading long.
 
ozzy and german, thank you. i really like the larue w/ t1 micro if that is correct it is all easily available.
i read the first 20 and last 20 or so pages of the mod holland over at arfcom.
lot of info to sift through....
 
Everyone I have talked to for the most part agrees that 8202XBR is the ticket for this style rifle. Have you experience any seating depth issues with the TMK?

Went out and tried this just for you today.

Same 23.4 load as I listed earlier, but instead of the 1.820 ogive oal, I pushed it back another .010 to 1.810 and loaded 10 rounds of it to take out.

While the 1.820 is reliable and shoots .7-.9 constantly, I managed one group right in there at 3/4 an inch, and the other was basically 1 ragged hole with the 1.810. The only downside is I think that this is right on the line pressure wise as I was getting a slight cratering of the primer, but it was 106 outside, so using this in the future will be fine as far as not having to worry about temperature increasing the pressure any more.
 
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106°. Fuck that. We were roasting at 92°yesterday, but we had 75% humidity

RE: The powder in the sun. Jeff T shot a 284win in the TN State F Class Long Range Championship this weekend. Day 1 was hot and humid but overcast and it rained half way through match 2 dropping temps into the high 70s, low 80s. His scores were mehhhh for him and he wasn't happy at all about the load/ barrel. Day 2, very light clouds. Heavy sunshine all day. 85° at first shot 92° air temp at final but ground temp must have been close to 100°. He set his ammo out on the line to cook in the open sun from the time he pulled his shit to the line. Shot two high X count cleans. That's with a heavy (I won't publish it) load of H4350, which is probably the most temp stable powder I know of save for maybe Varget. There is certainly something to this.

you guys have me motivated to try the 8202 now, just to see if I can improve on what I have.
 
106°. Fuck that. We were roasting at 92°yesterday, but we had 75% humidity

RE: The powder in the sun. Jeff T shot a 284win in the TN State F Class Long Range Championship this weekend. Day 1 was hot and humid but overcast and it rained half way through match 2 dropping temps into the high 70s, low 80s. His scores were mehhhh for him and he wasn't happy at all about the load/ barrel. Day 2, very light clouds. Heavy sunshine all day. 85° at first shot 92° air temp at final but ground temp must have been close to 100°. He set his ammo out on the line to cook in the open sun from the time he pulled his shit to the line. Shot two high X count cleans. That's with a heavy (I won't publish it) load of H4350, which is probably the most temp stable powder I know of save for maybe Varget. There is certainly something to this.

you guys have me motivated to try the 8202 now, just to see if I can improve on what I have.

106 isn't that bad as we barely ever break 15% humidity here. Just a few weeks ago I was out and it was 119; you basically have to wear long pants and a loose BDU top to go out there and not get burned by the sand and rocks.

There are also times of the year here where you can get a 30-40 degree temperature shift within one day and your DA will be all over the place.
 
106 isn't that bad as we barely ever break 15% humidity here. Just a few weeks ago I was out and it was 119; you basically have to wear long pants and a loose BDU top to go out there and not get burned by the sand and rocks.

There are also times of the year here where you can get a 30-40 degree temperature shift within one day and your DA will be all over the place.

Ever mess with Lapua 223 brass? I cleaned and cut the crimp out of a pile of LC brass, but I don't love the looks of it (haven't actually tried reloading so may be fine). Thought about finding a sale on the 223 and just snagging some.
 
Ever mess with Lapua 223 brass? I cleaned and cut the crimp out of a pile of LC brass, but I don't love the looks of it (haven't actually tried reloading so may be fine). Thought about finding a sale on the 223 and just snagging some.

Not in 223/5.56.

I use all LC 5.56 that they sell in the black bag with 250 of them in it from time to time.

I do have piles of once fired 5.56 LC but haven't loaded any of it, just sorted it by headstamp.
 
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View attachment 6940231Breacher, liking that paint job!
These arms rings are really bad.
I guess we're spoiled by (mostly every other) company paying attention to the scope mounting surfaces.
Lapped these a fair bit already...

By far one of the weakest parts of the MK12 are the awful ARMS #22 rings. I've threatened to swap them for NF ultralite rings more than once, and if I had a Holland that's exactly what I would run.
 
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By far one of the weakest parts of the MK12 are the awful ARMS #22 rings. I've threatened to swap them for NF ultralite rings more than once, and if I had a Holland that's exactly what I would run.

my badger 20moa riser came directly from a 5th GRP sniper locker. Traded an operator an extended rail he needed for it. They got rid of the QD rings on a lot of rifles and just bought badger units with a purchase card. I know its technically not "spec" but these things got tailored to the shooter so often I'm comfortably keeping the moniker.
 
My daughter's boyfriend running my mod0. AEM5 can. I went with a badger riser and rings like my buddies unit downrange. They shitcannned the QD rings. I started with my M3 variable (love it) but find the fixed parallax works better for what I use this rifle for. 32mm NXS becusse I can't bring myself to spend $1800 on a 24mm yet.

View attachment 6938093

Another soldier buddy shooting Highower at 600. (I know the can is illegal but F it)

View attachment 6938103

I love this rifle and after running it a couple years , find it is my favorite out of all my rifles, to include a bunch of high end custom match rifles and my mk13s. It just works.
How far out can you take that out?
 
How far out can you take that out?

The range is set up a little odd, but that's due to sink holes that can't be farmed, which is why we have the range in the 1st place so I'm not complaining. It goes from 600, 750, 1000, 1250. I have not taken it past 600, but I would think I could make hits on full sized IPSCs fairly easy at 750 once I had wind. The problem would be spotting hits. 600 is hard enough, as the "splash" from a 77 SMK is tiny and it doesn't ring out like a whack from a 47L.

We have taken 20" service rifles to 1k with 80gr SMKs over 24.4gr Varget so I am positive it'll get there, but I wouldn't be able to shoot a group worth a shit. It would be more like harassing fire.
 
Went out and tried this just for you today.

Same 23.4 load as I listed earlier, but instead of the 1.820 ogive oal, I pushed it back another .010 to 1.810 and loaded 10 rounds of it to take out.

While the 1.820 is reliable and shoots .7-.9 constantly, I managed one group right in there at 3/4 an inch, and the other was basically 1 ragged hole with the 1.810. The only downside is I think that this is right on the line pressure wise as I was getting a slight cratering of the primer, but it was 106 outside, so using this in the future will be fine as far as not having to worry about temperature increasing the pressure any more.

Was messing around with this and be careful seating the rounds much further in; the pressure spike was giving me flatted, cratered and pierced primers.

Sadly, my Mod1 absolutely loved the 23.4 load that was .010 further back.
 
Was messing around with this and be careful seating the rounds much further in; the pressure spike was giving me flatted, cratered and pierced primers.

Sadly, my Mod1 absolutely loved the 23.4 load that was .010 further back.

The TMKs of all flavors seem to build pressure at lower charges. I did not feel comfortable going above 23.2 to keep the load OK across multiple rifles.
 
The TMKs of all flavors seem to build pressure at lower charges. I did not feel comfortable going above 23.2 to keep the load OK across multiple rifles.

The higher BC is from them being longer; thats the problem.

I may end up trying to use a SMK or Nosler at the deeper seating depth and see what happens.
 
this works better


I put one on my wife's RECCE. The tips of the prongs made contact with the end of the blast chamber in my can with just timed peel washers. We had to remove it and cut about .040" off the back to shorten it and it's been fine since. Before that modification, the can would shoot loose, it's never done that on my Allen units.
 
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My daughter's boyfriend running my mod0. AEM5 can. I went with a badger riser and rings like my buddies unit downrange. They shitcannned the QD rings. I started with my M3 variable (love it) but find the fixed parallax works better for what I use this rifle for. 32mm NXS becusse I can't bring myself to spend $1800 on a 24mm yet.

View attachment 6938093

Another soldier buddy shooting Highower at 600. (I know the can is illegal but F it)

View attachment 6938103

I love this rifle and after running it a couple years , find it is my favorite out of all my rifles, to include a bunch of high end custom match rifles and my mk13s. It just works.
Do you prefer the AEM5 can over others like the SPECWR from SilencerCo. I know the SilencerCo isn't the correct can for the build. I am looking at building a MK12 Mod 1 soon. I just can't decided if I want to order another can or just use the one I am currently waiting for.
 
I'm going to our another one if these together, either a H or 0.
But a little looser guidelines like using any scope that's in the system.
Thinking nightforce 3-15 nos.
What would you guys go with in this situation ?(other than a 4k s&b?
 
Do you prefer the AEM5 can over others like the SPECWR from SilencerCo. I know the SilencerCo isn't the correct can for the build. I am looking at building a MK12 Mod 1 soon. I just can't decided if I want to order another can or just use the one I am currently waiting for.

I can't speak to any other 223 can. I ordered the AEM5 when I started the build and to perfectly honest I love it. Sounds good. Accurate, repeatable and reasonably priced. I switch it between my mod0, a 20" "mod10" and my wife's RECCE and its rock solid on all three.

Of I was going to deviate from the Ops12 can I would probably get the 30 cal version, just so I could run it on a large frame too.
 
Any of you guys have eye relief problems using 2 piece rings on a flat top before the handguard?
man i would think, i guess it depends on the scope but ive got mine mounted well ahead of the charging handle and with my nose touching the charging handle it is just black around the edges. youre talking at least an inch probably closer to 2" behind that.
BUT i see plenty mounted that way.