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My Mk12 Heavy Build **RANGE REPORT 5-2-25** See below (Page 1 of 2)
Posted: 4/24/2025 7:28:37 PM EDT
[Last Edit: Bowhntr6pt][Edited]
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I'm going to try and update this thread concerning my venture into building a Mk12-ish "Heavy" in .308. I received some key parts today from PRI which were ordered on Monday. First off, every time I call PRI I get a nice lady on the phone... she transfers me to a guy (damn, I forgot his name) who has always taken the time to guide me on builds and this .308 project garnered the same assistance and help. For the Aero M5 receiver sets you need the DPMS .308 Gen III CF Forearm Rifle Length part #03-072-14DE (DE is for the FDE). Well... excitement turn to a downer when I realized NONE of my various barrel wrenches work on the barrel nut. I assumed one of my DPMS LR-308 wrenches would work but no dice. I should have asked... I had thought about it earlier in the planning stage but forgot. So tomorrow I'll order a wrench and a couple other small items. I figured out that the top rail on the Gen III HG has to come off in order to install the full rail that ties the upper to the HG. No big deal, was quite easy to get the screws started. Below is a "soft assembly" with the parts just in place and not tightened down... I simply couldn't resist seeing what the end product would look like. I'm waiting on a Timney trigger, Harris bi-pod, and FDE sling to finish this rifle off. Then I'll clean the barrel really good, hit the range, and cross my fingers that all the parts play nice together. Some of the parts...  Soft Assembled...   Please don't post negative stuff about doing such a build such as the design is outdated, it's too much money for what it is, it's too heavy, .308 sucks should have went (fill in choice cartridge) yada, yada, yada, seems several people on here always do that and I bet they have never owned what they are bashing nor do they own what the are recommending. If you can't afford to screw around with various projects and builds just for the hell of it... just move on and avoid this thread. This is only for those interested in doing such a project. |
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Originally Posted By Marsh_Rat: Nice! Good choice on the Mk4 4.5-14. I’ve thought about doing that to my Armalite AR-10, as it would be cool to have a larger version of my Mk12. I already have a AEM5-30. The suppressor is on my short list. I have two of the FDE 3.5-10 MK IV's but they are on a FDE Mod O build and a Mod H build. They are just a little pricy now if you can find them. |
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That’s cool. I had Monty at Centurion Arms build me a 5.56 MK12 a few years ago. I didn’t care about making it a clone so I went with better glass, mount, back up sights and Surefire can etc… Turned out great and it’s a laser beam with BH 77gr OTM Point is you built a cool gun with quality parts that you like. Looking forward to seeing some groups from your new blaster. Attached File |
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Originally Posted By EdgecrusherXES: How does it shoot OP? I can dig the build and the SCAR coloring theme.  I have not tightened everything down as none of my wrenches seem to fit the barrel nut. I'll have to order the proper wrench so it's it's going to be a week or more until I can hit the range. |
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Originally Posted By NTXGlocker: Nice. It only has to please you. How heavy is it? Great question… I don’t have a scale and I’m bad at guessing. No where near as heavy as my DPMS 18” SASS/Mk12ish rifle. I was kind of surprised at the weight, it has some heft to it but to me lighter than I anticipated. I’ll see if I can figure out a weight when I get it all back together. |
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Originally Posted By Phiers: Sexy. Love it. I did the same thing but in 6arc and a proof barrel. I was tempted to go 7mm-08, after this one gets done, maybe I'll find someone to spin me a barrel. PRI was closed today apparently, have to wait until Monday. I did score ten boxes of PPU Match (168gr) ammo at $10 a box.  Not sure of PPU's quality but for $10 a box not much of a risk. |
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Originally Posted By olekennyroy: Very nice OP. Big savings over the PRI complete rifle? I need a 308 AR, and I'm really digging the Mk12 (or is it 10) build. You can go to PRI’s site and spec out the parts you want. I already had the Aero receiver set, BCG, charging handle, and some other small parts so my basic rifle build was slightly cheaper. |
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Originally Posted By Bowhntr6pt: I was tempted to go 7mm-08, after this one gets done, maybe I'll find someone to spin me a barrel. PRI was closed today apparently, have to wait until Monday. I did score ten boxes of PPU Match (168gr) ammo at $10 a box. https://imagizer.imageshack.com/v2/640x480q70/922/3PbUkS.jpg Not sure of PPU's quality but for $10 a box not much of a risk. Originally Posted By Bowhntr6pt: Originally Posted By Phiers: Sexy. Love it. I did the same thing but in 6arc and a proof barrel. I was tempted to go 7mm-08, after this one gets done, maybe I'll find someone to spin me a barrel. PRI was closed today apparently, have to wait until Monday. I did score ten boxes of PPU Match (168gr) ammo at $10 a box. https://imagizer.imageshack.com/v2/640x480q70/922/3PbUkS.jpg Not sure of PPU's quality but for $10 a box not much of a risk. That ammo is decent. It should group around 2 MOA in a decent barrel. It's not FGMM, but it's better than M80. For $0.50 that was a great deal. Those boxes are the older stuff from around 2005ish. Around 2010 they switched to a blue box, but the ammo quality remained consistent. |
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RANGE REPORT 5-2-25 OK... I finally got to the range to shoot this build. In FULL DISCLOSURE the range was only EIGHTY YARDS (80), I had to use a picnic table, and I was shooting dead west with the damn sun in my eyes. Ok, now that the excuses are out there, I will say from a comfort level during shooting I was at a 9/10. I wasn't as comfortable as I'd like to have been and I had to be careful for so as not to slip the bi-pod legs off the front of the table... but with all of that I must say all but one shot felt great. I had to make due with what I had and for the most part, I believe the results were acceptable, representative of the rifle, and I have nothing to blame. All shooting was from a bi-pod and rear bags. My first two five-round groups had a jam mid-mag so I swapped out the mag and no more issues. This mag is new and of unknown maker, it's FDE in color and looks good in the rifle but if it continues to cause issues I'll toss it. First Shots/Impressions: What a relief when the rifle functioned, including last round bolt lock. Many time we build these things, even using nice parts, and sometimes the parts don't play nice. Recoil was smooth and pleasant to shoot. Obviously much more comfortable to shoot than my 16" MLG rifles. Extraction and ejection was strong and positive exiting out at about 4:00 to about six to eight feet. Most of the cases ended up in the same general area. UPDATED PIC  Ammo Use: I fired three (3) rounds Federal 150gr FMJ to get the scope on; twenty (20) rounds of FGMM 168gr; ten (10) rounds Hornady 168gr TAP; and five (5) rounds PPU 168gr Match. I ran out of time or I would have fired more. All groups below are five (5) rounds from the magazine. RESULTS- First five rounds (1-5) 168 FGMM  Second five (rounds 9-10) 168 FGMM  Last Two Groups 168 FGMM (shots 21-25 and 31-35)  First and second groups of 168 TAP (shots 11-15/16-20)   First five PPU 168 Match (shots 26-30)  With all this out of the way I can honestly say I'm quite pleased with the build. It seems to me towards the end the performance of the FGMM ammo improved over the initial sets of fire. I am confident that with some more rounds down the tube it will improve some... maybe... hopefully. Looking at all the groups combined the rifle seems to be consistent, no real odd outlying rounds and no real stringing to speak of. I look forward to your thoughts and critique. |
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Originally Posted By Phiers: Sexy. Love it. I did the same thing but in 6arc and a proof barrel. That’s a damn good idea. If I buy another 6ARC Lilja barrel, that’s what I’m doing. Then I’ll have a “daytime” version of my hawg rifle. OP, really good looking rifle. |
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Originally Posted By SuperJlarge: Nice build OP! What barrel? You may want to try some 175’s. In my PSA Sabre, which has what I believe to be a faxon barrel, the 168’s have been meh, but the FGMM 175’s have shot well. @SuperJlarge Thanks. Barrel is Douglas from PRI. I have some 175 loads stashed away... just too damn hot right now to do any testing. |
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Wonderful build !! I'm not sure how I haven't seen this until now , but I like this very much ! I suggest trying some 155gr Hornady Amer. Gunner ammo as well, that ammo has done very well for me in the past. I bet accuracy from the Douglas barrel will only get better after a break-in. |
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JAFOM.... Just another fat old man.
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Originally Posted By Nameless_Hobo: I have been wanting to do the same thing in 6.5 creedmoor. Seems like it would be a fun build. I just ordered an X-Caliber barrel in 7mm-08. I will call them in the am to see if they can profile the barrel for use with the AEM5-30 suppressor. |
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Originally Posted By Bowhntr6pt: I think I found the load... Hornady 168 HPBT Match with 42.5grs Re15 and Remington Magnum primers set at 2.810" COAL. https://imagizer.imageshack.com/v2/640x480q70/922/hwvr7d.jpg https://imagizer.imageshack.com/v2/640x480q70/924/CuhODQ.jpg Looks like a good shooting rig OP. Care to drop a breakdown of the parts list? I officially now have the itch to build a Mk12 Heavy 
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Let's Go Brandon!!!
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Originally Posted By eddster: Looks like a good shooting rig OP. Care to drop a breakdown of the parts list? I officially now have the itch to build a Mk12 Heavy @eddster Aero Precision upper, lower, their High-Pressure BCG, receiver extension, standard rifle buffer, standard spring, and Breech charging handle. Precision Reflex Douglas barrel, Gen III HG, Top Rail, Flip up GB Sight, Rear Sight. Allen Engineering brake and collar. ADM QD mount with Leupold MK IV 4.5-14x50. Harris 6-9 swivel bi-pod. Timney trigger. With a rifle length gas system, the weight of the rifle (large frames are not light weight) and loads at the lower end this thing is a sweet shooter. |
| Looking and shooting, good, my friend! I’m way overdue to hit the range and after shooting bourbon with you. Gotta make it happen. |
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My Mk12 Heavy Build **RANGE REPORT 5-2-25** See below (Page 1 of 2)
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