So I'm interested in doing some longer range shooting on a range that has steel every 100 meters out to 600. I've got a 5.56mm 14.5" BCM ultra light weight fluted barrel with a Surefire RC2 suppressor which is awesome for the original 100 meter max rifles matches I used to do, but I think once it heats up it's not staying accurate past 200 yards. I'm having real trouble hitting a 6" gong reliably after 20 shots. Cold bore seems to work better. So I'm looking for a complete upper I can just drop on to get me going, and I've seen the PRI MK12 18" gen 2, linked below. I've also seen a similar one from CMMG that's a medium taper barrel. Any reason not to go with one of these for up to 600 yards? It wouldn't surprise me if what I have now is 2-3+ MOA, and I'm looking for 1 MOA or better. Thanks.

https://www.precisionreflex.com/upper-assemblies/646-2129-18-mark-12-mod-0-spr-gen-ii-upper-in-556-cal-1-7-twist-black.html#/61-colors-flat_dark_earth

https://cmmg.com/upper-group-endeavor-mk4-5-56x45mm-nato-18

If aren’t worried about building your own there’s a lot you can do and better than the PRI mk12. Don’t get me wrong I love me some
Classic mk12 but you can also buy a really nice Criterion barrel etc and end up with more accuracy potential.


I’d first say try your current 14.5” with a good optic and mk262 or equivalent ammo  then go from there.

If it’s a rifle for steel, a 24” bull barrel could be a lot of fun.

Your options are pretty much limitless. Free float a good barrel. You’ll want 1:8 or 1:7 twist.

Get a good trigger. Get a good scope. It can really be anything you want it to be. I shot a 16” barrel at little pieces of steel out to 700 yards today with 75gr BTHPs.

Alright, so basically just swap the barrel instead of a whole new upper. I'll have to see what my options are for that.

If you build, I can vouch for the Ballistic Advantage 18” fluted premium bbl’s.
definitely sub MOA

Must be 18"?

Mk12s look cool, but if you're concerned with long range terminal performance, a 16" 1:7 barrel would be indicated since it'd enable you to use the 77gr Tipped Matchking in cold weather. It exhibits a very low expansion threshold of 1500 fps, a high ballistic coefficient and devastating closer range fragmentation. If it's fired out of a barrel longer than 16", however, it can underpenetrate at close range. The Lantac Recon rifle is a potential candidate, as I imagine you'll want the greater precision of a stainless barrel. I'd replace the Dragon brake with a Warcomp or SF3P (since you already have the silencer) if you intend for this to be a fighting rifle since the Dragon exhibits significant flash.

If you're purely concerned with precision and don't care about terminal performance, however, the Mk12 or an even longer rifle would be a reasonable choice for slinging OTMs. I've consistently heard that they print tighter groups than the TMK, though I haven't seen the difference since I've never group tested my rifles with TMK. They are also much easier to find and potentially much less expensive.

You could also try some kind of barrier blind soft point reload in a long barrel, but this would still sacrifice some expansion range relative to the TMK from the 16" barrel. Truly barrier blind bullets are not available to most civilians in full house 5.56mm cartridges, so you'll have to reload them. I say "most civilians" because some distributor programs allow EMTs, firefighters, airline pilots and some oters to buy LE/veteran ammo. Stupid stuff.

I just picked up a new 18" wilson combat urban super sniper barrel to try... who named these barrels anyway?

I recently got the pri MK12 upper and slapped it on an m16E1 lower. I love it . I’ve been able to make hits on standard IPSC targets out to 850 and the 900 yard gong which is admittedly 36”. It shoots great , get one if you want one.

Why not build a MK12 upper and use a White Oak or better barrel instead. You’ll be into it for the same cost and can apace out the purchases of need be.

I've assembled three MK12 type builds. Some of the parts I acquired off the EE at really good prices, including a Douglas barrel, kind of how I ended up with three.

I have them with barrels from Douglas (CLE), Criterion (Craddock Precision), and Ballistic Advantage. I had to return two prior barrel to BA after getting horrible performance and damaging my AEM5 suppressor, I made a detailed post with pics a couple years ago so I do not recommend BA unless you want to play "roll the dice" with the barrel you get. Just too many issues in the past couple years with BA.

The rifles are my favorite to plink and shoot steel with. On the heavy side, but soft shooting. If you like to build, have at it. If you want a no-hassle way of getting a great shooter, just get an upper from PRI and call it a day. Buying one from PRI will eliminate the chances of getting frustrated with a build if it has issues, especially after spending a lot of money.

If you are coming from a 14.5" ELW fluted barrel I think you will severely underestimate how heavy an 18" SPR profile barrel actually is (.850-.860" under handguards).

Because of that, I did a custom 16" medium heavy .775" midlength fluted barrel, 1/7. Weighs 3/4 pound less than the SPR 18" un-fluted. The 18" only gives 15-25y additional terminal performance range over a 16" and zero improvement on elevation and windage inside 600y. Plus the 16" has less cantilever weight with suppressor mounted.

I shoot 77 grain TMK or SMK handloads. I also reccomend a .223 match chamber over a .223 Wylde. The 223 Wylde is just a negative if you handload and don't shoot rounds loaded so long they don't fit in the magazine. 223 Wylde is fine if you must shoot factory 5.56 77 grain ammo.

I had Centurion Arms build mine a couple years ago.

Monty is an outstanding guy and extremely knowledgeable

It does very well with BH 77gr OTM

I went with NF ATACR and Surefire can because I wasn’t interested in clone.

Attached File

PRI makes excellent gear, and the Douglas barrel in that Mk12 is going to be an excellent performer with heavier bullets like the 77gr Mk262 ammo designed for use in that system.  With that being said, the Mk12 is a heavy system, partly because of the barrel contour (which is beneficial for heat management during long strings of fire), and partly because the handguard and continuous top rail are heavier than more modern rail systems.  I skipped the top rail on my Mk12 build because it saved 3/4 lb, and a modern cantilever optic mount makes it redundant.

If you want a Mk12, then by all means get a Mk12 - that's what I did (mostly), and I don't regret it one bit.  But if you're just looking for an upper that performs better at long range than your current BCM, you can build your own custom rig around a barrel from WOA, CLE, or Craddock Precision, and make it exactly how you want it.  

A word of advice: the 1-7 twist rate is better for stabilizing the heavy/long projectiles (77gr + lead and 70gr + copper bullets) and the rifle length gas system makes for a really smooth operating system.  The 1:8 is fine for stabilizing most factory ammo, but if you get into reloading longer bullets, it might have trouble stabilizing them with the slower twist rate.

https://www.whiteoakarmament.com/5spr18.html

https://compasslake.com/product/douglas-ss-1-7-spr-mk12-18-1/

https://craddockprecision.com/signature-series/

1:8 twist stabilizes every bullet up to and including 80+ grain match bullets. The USAMU uses 1:8 for 200/300/600 yard tournaments, 1:7 for actual 1000 yard tournaments because the faster twist helps at the longer range.

1:8 or 1:7 will shoot 52/53 grain match bullets lights out inside 200 yards.

I love PRI products, but am not a fan of Douglas barrels. CLE and WOA are my go to sources for new barrel nowadays. Wilson Combat and Noveske get an honorable mention.

Never buy a bull barrel from anyone, especially a 24" or longer model. You simply don't need that heavy of barrel to get good groups. Any SPR profile will shoot just as well and not give you a hernia.

What do you guys think about noveskes mk12 offerings vs the pri stuff.