Mk12 Mod 0 vs Mod H performance?

[kb1]

Just put together a Mod 0, and as cools as it looks, it's a bit of a pig . It's not a whole lot lighter than my 16" .308. How much more performance do you get out of a Mod 0 than the Mod H? Do 2" of barrel make that of a difference? When I get my stamp back on my AEM5, the Mod 0 is gonna pretty damn long as well.

 

[Slevin182]

Probably not a lot of difference in MV. 50-75fps. I'd take a high quality 16" over a mediocre 18". When I was putting together my "SPR-ish" rifle, I obviously had influence from the original, but had a "what would the setup be today?" mentality. The answer is probanly not an AEM5 at all, but they look so darn cool I had to keep that. Yes, an 18" with the AEM5 on the end is heavy. Especially if you're going mod 0 with the top rail. Today's cantilever mounts are so good, I didn't see where the top rail would get me anything. I plan on taking my 18" "SPR" down to 16", and keeping my 13" MCMR. Already had the rail shaved down so the AEM5 will be a flush fit with the 16" barrel. Less weight, more compact, heavy can isn't as far out. I've shot other 16" 223 ARs out to 400 yards no problem, which is about as far as I would take a shot meant to be lethal with the setup.

 

[gac700]

I have both and prefer the O. Wish I hadn’t scratched the H itch, but did. O is heavy with an AEM5, but the combo works extremely well. It is fun showing people how quiet this system is - truly impressive. You’ll be spoiled.

The small weight saving that the H offers isn’t worth the money spent - at least to me. Wait on your AEM5 and enjoy your build.

 

[thehun]

Prefer the 0 as well...

 

[RTV]

The Recce Rifle: Builder's Guide to Modern Classic - Everyday Marksman

The original SEAL Recce Rifle was an in-house modification to M4 carbines. The history goes back to the early 1990s. Since they were so individualized, there really wasn't a spec. But we do know that Lilja barrels and optics in the 2.5-10 range were popular. The original intent was to allow...

www.everydaymarksman.co

This article has been my RECCE/SPR build bible.

 

[kb1]

Good read. Thanks!

 

[thehun]

Great read. The Mk12 platform is just awesome regardless which mod you get.

 

[nn8734]

Just put together a Mod 0, and as cools as it looks, it's a bit of a pig . It's not a whole lot lighter than my 16" .308. How much more performance do you get out of a Mod 0 than the Mod H? Do 2" of barrel make that of a difference? When I get my stamp back on my AEM5, the Mod 0 is gonna pretty damn long as well.

I had a mod 1 that I converted to a Mod H for the reasons you state, specifically the oal. I’m getting 2770 using 77smk via my hand loads and have no problem hitting 2/3 ipsc at 800 yards with the mod H

 

[RyanScott]

Had dinner with a group one time that included a guy who killed a Taliban at 900 yards with a Mk12. Also a guy who used an M4 with RCO and green tip at 600. These things don’t bounce off even at extreme ranges for 5.56.

 

[RTH1800]

I prefer the 18" and have used both extensively. I also prefer the Mod 1 for weight savings and no loss of accuracy. I prefer the Mod O for esthetics but sold all of mine due to weight issues.

 

[drewthebrave]

TLDR: If you want a Mk12, build a Mk12. If you want a lightweight gun, build a lightweight gun. Just don't expect the 2 to overlap without taking some exceptions to the original design.

The 2" difference in barrel length won't make much difference in terms of weight or performance. The heart of the Mk12 is the barrel, so I don't really think you can change to a light profile and still consider it a Mk12. Whether you go with a 16" or an 18" barrel, the difference is only an ounce or two - which isn't really going to change the way the gun feels. If you go with a light profile barrel, then you might as well just build a 3-gun rifle and forget any pretense of building a Mk12.

While I've always wanted a Mk12 Mod 0 style rifle, I thought that technology had advanced in the following decades and that I'd rather have a lightweight rifle. So I built around an 18" LaRue PredtAR barrel and Geissele Mk4 rail to have a middle-weight, do-everything gun. While I'm really happy with how it turned out, nothing really compares to a Mk12, and I'm going through the process of building a Mk12 anyway. I learned a lot from that build, so I don't regret it, but if I built the Mk12 first, I probably would have skipped the 18" lightweight gun for a more handy 14.5" Recce/3-Gun style build (that I'm also working on).

However, if you don't care about having a "clone-correct" gun and want to cut some weight from the Mk12 Mod 0, I think the heavy SWAN sleeve is obsolete, as it just adds redundant weight to allow for 2-piece rings to be used. Now that modern optic mounts are available in cantilevered designs, they get you to the same goal (precision oriented optics mounted on the AR platform) without the added cost & weight.

Living in California, my Mk12 is going to be some sort of abomination regardless, so I figure I'll just build it the way I want and be happy with it. The "purists" may balk at the franken-gun construction, but I'm not building mine for the purists -- I'm building it for me. My Mk12 (Mod CA?) is going to utilize the Gen3 Delta rail, skip the SWAN sleeve, have a featureless grip, use a carbon fiber stock (Lancer), and obviously skip the suppressor since my state won't allow them. If I ever move to a free state, a suppressor will be at the top of my to do list, and at that point I may consider more "clone correct" parts. But as long as the barrel, handguard & brake/collar are there I'll be happy enough. Attached is a mock-up that shows the general idea of what I'm planning (with some substitutions for parts not on gunstruction).

 

[ST42]

Hotel, all day and everyday........

 

[clcustom1911]

Honestly, the featureless grip for CA bullshit is kinda convenient for those that don't wrap their thumb around the grip for precision stuff anyway.

I'm lefty so, I always ran my thumb on the selector side anyway.

So, featureless + ambi selector and you right handed folk are in business.

I moved to a free state so, I can have non-neutered stuff anyway. Can't wait to get back from middle east and piece together my Mod O.

 

[SilencedShooter11B]

I had a mod 1 that I converted to a Mod H for the reasons you state, specifically the oal. I’m getting 2770 using 77smk via my hhh mail we vhand loads and have no problem hitting 2/3 ipsc at 800 yards with the mod H

curious what your load is to get 2770fps from a 16” barrel with 77gr.

 

[nn8734]

curious what your load is to get 2770fps from a 16” barrel with 77gr.

it’s a toasty one that if you want to duplicate, work up. Primers show mild cratering, brass sometimes has slight extractor marks.

77smk | 25.3g tac | Remington 7-1/2 | Lake city case.

above MV was taken in summer, temp was 97 (shade), humidity was less than 5%, DA was over 6000. Location was outside Vegas.

I also have a more mild node at 24.3 which is ~70 fps slower.

 

[CrabsandFootball]

The 18" is inherently more reliable due to longer distance between muzzle and gas port. Its possible to tweak the gas port size to help this but its a gamble.

 

[Steel head]

curious what your load is to get 2770fps from a 16” barrel with 77gr.

It’s easy to do if your not concerned with reusing your brass.

 

[j-dubya]

The 18" is inherently more reliable due to longer distance between muzzle and gas port. Its possible to tweak the gas port size to help this but its a gamble.

Please expand upon this, since the distance on an H/mid length port to muzzle is longer than on a rifle gas 18”...

 

[clcustom1911]

Please expand upon this, since the distance on an H/mid length port to muzzle is longer than on a rifle gas 18”...

More dwell time from the time the bullet passes the gas port to when it exits the barrel. More time and volume for the gasses to expand and drop just a tick. Makes for better conditions for the casing in the chamber to shrink back down so it will be extracted more easily, less gas pressure going back is less bolt speed which means less energy battering the bolt and carrier over time.

Make sense?

 

[j-dubya]

More dwell time from the time the bullet passes the gas port to when it exits the barrel. More time and volume for the gasses to expand and drop just a tick. Makes for better conditions for the casing in the chamber to shrink back down so it will be extracted more easily, less gas pressure going back is less bolt speed which means less energy battering the bolt and carrier over time.

Make sense?

I think you need to go back to the second half of what I said in regards to what I was responding to...

 

[Steel head]

I’ve shot SPR barrels and a few 14.5 and 16 middys.
Fairly similar feel but the 14.5 middy was a bit touchy.
16”middy is noticeably nicer than carbine gassed.

Still love how my SPR build shoots, so smooth.

 

[clcustom1911]

I think you need to go back to the second half of what I said in regards to what I was responding to...

You are definitely correct, and I cant read properly at 3am where I am LOL. Based on my experiences, rifle length gas systems just shoot softer in general which is probably due to the longer, I guess, pre-dwell time. Gas port sizes have a great deal to do with recoil as well.

 

[j-dubya]

You are definitely correct, and I cant read properly at 3am where I am LOL. Based on my experiences, rifle length gas systems just shoot softer in general which is probably due to the longer, I guess, pre-dwell time. Gas port sizes have a great deal to do with recoil as well.

All good. I think a better apple to apple comparison would be a 16” intermediate gas, which is still quite capable in the operating envelope when feeding it 5.56 pressure ammo. Even a rifle gas 16” in a dedicated suppressed system works.

 

[clcustom1911]

All good. I think a better apple to apple comparison would be a 16” intermediate gas, which is still quite capable in the operating envelope when feeding it 5.56 pressure ammo. Even a rifle gas 16” in a dedicated suppressed system works.

I have a 16" mid. Shoots softer than a carbine, tad more rough than a rifle with 20" barrel. If imagine 18" with rifle is between mid/16 and rifle/20. I'll have a head to head comparison in March when I get back state side with my PRI Mk12/0 build.

 

[TheGerman]

I have a Mod1 and a ModH. Also used the Mod1 a decent amount of the time while deployed.

The Mod0/1 is a jack of all trades gun. It doesn't do fantastically well at longer ranges mainly due to the small projectile and terminal ballistics, but it works. It doesn't do anything great at close range either as its basically an 18" front heavy carbine with a big suppressor on it.

The way I set the Mod1 up was to have a suppressor pouch on the side/back of my ruck. If we weren't shooting at distance or at night, it came off. Offhand recoil managment and bringing it up on target with that suppressor on was just a slow, wobbly disaster. Put an index mark on the suppressor and Mk12 barrel to where it needs torqued, and you can have it on within seconds if needed. From my experience, the torque position actually matters.

Secondly, make sure the scope is far enough forward to when you change the stock position from your longer, precision gun shooting from prone/kneeling position, to your shorter 'use it like a carbine position' that your face isn't running into the back of the scope. Put an RMR on the 12 o clock instead of an offset as it will be significantly easier to hold/aim the rifle and simply aim via a piggyback 12 o clock RMR ontop of the scope,. than having to tilt the entire gun; the 12 o clock mount also allows you to use it with helmet mounted nightvision - the 2nd reason as to why making sure your scope isn't too far back is beneficial. This part really comes into play if you want to use the Mk12 as a do it all gun and do not want/need to carry an actual carbine/SBR with you ontop of the Mk12; I carried a carbine with me when I had a M110, but not with a Mk12.

Have ballistic data for both the Mk262 you'll shoot as well as for M855. I've had to use the M855 data once after running through all my 77g on station and noone having any. I'm pretty sure that started a rumor about how they are 'the same round' after that.

The ModH is easier - you can put almost any scope/stock/bipod on it as long as you have the PRI ModH upper and its a 'correct' ModH. Everytime I see a picture of one, it has some even more random shit on it than the last one did.

 

[CrabsandFootball]

I have a 16" mid. Shoots softer than a carbine, tad more rough than a rifle with 20" barrel. If imagine 18" with rifle is between mid/16 and rifle/20. I'll have a head to head comparison in March when I get back state side with my PRI Mk12/0 build.

Not all 18" SPR's are running rifle length. Yea I know its not clone correct but many of the early 18" dmr barrels that were going overseas to units and contractors like the Noveske 18" SPR could be had in a mid gas system.

18" with a mid system is about a reliable as you will next to a M16A1/A2.

I remember guys like MSTN & G&R/Dennys making a shit load of upper batches and selling extras on the market back then.

It was found in testing that the mid gas system was more reliable in cold weather than the rifle gas system. The trade off is a little bit harsher shot but for guys getting dropped on the side of a mountain in afganistan, reliability is key.

Once you put the AEM or Ops in can on, its negligible as far as handling goes. I will always take the additional velocity if there is not a huge drawback.

 

[DeadZeppelin]

Every time I check out threads like this it makes me wish we didn't get rid of these guns.

The Recce Rifle: Builder's Guide to Modern Classic - Everyday Marksman

The original SEAL Recce Rifle was an in-house modification to M4 carbines. The history goes back to the early 1990s. Since they were so individualized, there really wasn't a spec. But we do know that Lilja barrels and optics in the 2.5-10 range were popular. The original intent was to allow...

www.everydaymarksman.co

This article has been my RECCE/SPR build bible.

Thanks for the good read.

 

[RTV]

Every time I check out threads like this it makes me wish we didn't get rid of these guns.



Thanks for the good read.

Welcome,
FWIW my current evolution on all this is to go even shorter than the Mod H.
there has been a lot of really good info coming out recently about the effectiveness of even shorter barreled 5.56 rifles like the 12.5" when using HIGH QUALITY ammo.
this kind of stems from what they talk about in the article about how when the big army got involved with the development of the RECCE/MK12 the SEAL teams who were running them from the get go felt that what crane came up with was a slower heavier less effective tool than what they started with.

long story short my current experiment is a 13.9" SPR type build reason being that after adding a suppressor (im going DA Nomad30) and everything to it it should be right around the same length as a 20" Barrel with the idea being that with a high quality round the effective range of even a shorter barreled rifle like that would be effective all the way out to 600/ 700 yards with something like MK262 which didnt become available until after the MK12 program...

Just my current experiment i could be full of ****

 

[DeadZeppelin]

Welcome,
FWIW my current evolution on all this is to go even shorter than the Mod H.
there has been a lot of really good info coming out recently about the effectiveness of even shorter barreled 5.56 rifles like the 12.5" when using HIGH QUALITY ammo.
this kind of stems from what they talk about in the article about how when the big army got involved with the development of the RECCE/MK12 the SEAL teams who were running them from the get go felt that what crane came up with was a slower heavier less effective tool than what they started with.

long story short my current experiment is a 13.9" SPR type build reason being that after adding a suppressor (im going DA Nomad30) and everything to it it should be right around the same length as a 20" Barrel with the idea being that with a high quality round the effective range of even a shorter barreled rifle like that would be effective all the way out to 600/ 700 yards with something like MK262 which didnt become available until after the MK12 program...

Just my current experiment i could be full of ****

I think you are on the mark. We are supposed to be migrating from the 10.3 inch shortys where I work, to 11.5 inch Shorty's because of the increased performance you get with that extra inch. When that happens I think I am going to turn my 14.5 into a recce/SPR rifle. Mk 262 is an awesome round.

 

[CrabsandFootball]

They will eventually go back to the 12.5, which is the optimal length IMO.

Colt and later on BCM figured out 11.5 was much more reliable and had better performance than the 10.5 and later 10.3 in a DI gun. Everyone is going to be running a can on these and with modern lowered blowblack suppressors and shorter OAL, it will nullify the barrel length being a bit longer.

 

[clcustom1911]

Not all 18" SPR's are running rifle length. Yea I know its not clone correct but many of the early 18" dmr barrels that were going overseas to units and contractors like the Noveske 18" SPR could be had in a mid gas system.

18" with a mid system is about a reliable as you will next to a M16A1/A2.

I remember guys like MSTN & G&R/Dennys making a shit load of upper batches and selling extras on the market back then.

It was found in testing that the mid gas system was more reliable in cold weather than the rifle gas system. The trade off is a little bit harsher shot but for guys getting dropped on the side of a mountain in afganistan, reliability is key.

Once you put the AEM or Ops in can on, its negligible as far as handling goes. I will always take the additional velocity if there is not a huge drawback.

Yeah man, I can't wait to get my AEM can. My barrel is a Douglas 18" w/rifle gas. Should be a hoot.

 

[Steel head]

Yeah man, I can't wait to get my AEM can. My barrel is a Douglas 18" w/rifle gas. Should be a hoot.

.104ish gas port?

 

[clcustom1911]

.104ish gas port?

Unknown. It's currently about 10k miles away

 

[hellishot]

I like both for different purposes.

 

[gconnoyer]

I dont think its going to make much of a difference either way.

You'll likely lose 50-70fps dropping 2"
You'll probably shed less than a pound losing 2" off the little barrel.

I say Mod 0.
You dont "gain" enough with the 16" in any way to justify stripping the velocity and super soft recoil on the 18"
My Mod0 only weighs 16.3lbs (without suppressor, on my bathroom scale)

 

[LANCER]

it’s a toasty one that if you want to duplicate, work up. Primers show mild cratering, brass sometimes has slight extractor marks.

77smk | 25.3g tac | Remington 7-1/2 | Lake city case.

above MV was taken in summer, temp was 97 (shade), humidity was less than 5%, DA was over 6000. Location was outside Vegas.

I also have a more mild node at 24.3 which is ~70 fps slower.

As good as TAC is, that is a seriously overpressure load (unless you're seating them 2.260 (long) Have you tried Accurate 2520 at around the 25.6 - 25.8 range? It delivers velocity at lower pressures but might spike at the top end. I can easily get 2775 in summer and 2750-60 in colder temps with only flattened primers in summer. No other pressure signs. Running a MOD 0 and headshots at 600, 2 inch swingers at 500, and consistent torso hits at 700. Have hit 800 but if it's variable-windy, don't waste your ammo. Also seated deep at 2.240 so you can play with pressure signs by seating slightly longer. Primer pockets get loose shooting suppressed with AEM-5, so I mainly shoot it un-suppressed.

 

[GhostFace]

AA2520 is a great powder for MK262 cloning, I can attest to the speeds Lancer stated. When I loaded for 5.56 I got 2785 fps using 24.5 grain in gaut brass. I could get more velocity by going a grain but I played it safe with the lower charge. Accuracy was very good too, su MOA out to 300 which was the furthest I had access to at the time.

 

[nn8734]

As good as TAC is, that is a seriously overpressure load (unless you're seating them 2.260 (long) Have you tried Accurate 2520 at around the 25.6 - 25.8 range? It delivers velocity at lower pressures but might spike at the top end. I can easily get 2775 in summer and 2750-60 in colder temps with only flattened primers in summer. No other pressure signs. Running a MOD 0 and headshots at 600, 2 inch swingers at 500, and consistent torso hits at 700. Have hit 800 but if it's variable-windy, don't waste your ammo. Also seated deep at 2.240 so you can play with pressure signs by seating slightly longer. Primer pockets get loose shooting suppressed with AEM-5, so I mainly shoot it un-suppressed.

Funny you mention AA2520 as I have a lb of it on the shelf and have been meaning to do an OCW with LabRadar using it. I’ll prob start at 25g and go to 26. The TAC load is definitely a pressure load but delivers consistent hits to 750m in reasonable conditions. I do have the load at 24.2-24.3 which has no pressure but velocity is around 2640ish.

I’ll prob shoot the ocw next week, and if I can develop a similarly consistent load w/2750 fps or so at lower pressures I’ll be on be hunt for some more 2520.

 

[CWalker]

I was in your same boat. 18” felt like a boat anchor once my can came in, so I built a 12.5” and it’s night and day feel wise. Yeah, I sacrificed some performance but it’s for fun and coyotes out to 350-400 max and it’ll do that just fine. Going from 18 to 16, I don’t think you’ll see much difference in weight/feel or performance. Pretty much will have 2 of the same rifle (not a bad thing tho lol)

 

[LANCER]

Funny you mention AA2520 as I have a lb of it on the shelf and have been meaning to do an OCW with LabRadar using it. I’ll prob start at 25g and go to 26. The TAC load is definitely a pressure load but delivers consistent hits to 750m in reasonable conditions. I do have the load at 24.2-24.3 which has no pressure but velocity is around 2640ish.

I’ll prob shoot the ocw next week, and if I can develop a similarly consistent load w/2750 fps or so at lower pressures I’ll be on be hunt for some more 2520.

AA2520 seems to be fairly plentiful, as most people don't know about it nor is it advertised all over the place for .223 so even today you could probably find a keg of it.

The 2639-2640 fps TAC load is an accuracy node in most SPR profile barrels. I've had 1/3 inch groups with it but it's too slow for any meaningful distances. 2700-2750 of course is the sweet spot for 700, although higher than 2750 is desired to stay in the transonic range out to 800. Some of my loads right now are running around 2700 in the cold weather which go transonic at 666 yards and are subsonic at 800 (which correlates what I saw last weekend, only hitting 800 1 in 5 shots. 700 was like a laser though. You'll be able to hit 2750 no problem with AA2520. I've been using Federal brass and GM205MAR primers in this batch, which gives lower velocity, but better SD. CCI #41 will give slightly higher velocity but slightly worse SD all else being equal. I also save my brass hence I'm a bit more conservative in my loads.