Mega Machine Monolithic AR308 build

[praff]

Ok...I don't really do this very often, but out of the projects I have tackled, this one seems to be the most rewarding so I thought I would share.

I have been searching for a suppressor host for my YHM phantom 30 cal can and have sampled a couple rifles. I owned a M1A socom and a cheaper FAL recently. Neither of these really rang my bell. I really didn't want to spend the cash on a high end 308AR, but bit the bullet and did it a little at a time. My goal was to build a sub moa battle rifle.

I ordered a Mega Machine monolithic uppper and ambi lower combination and all I can say is wow. This stuff is the nicest kit I have had the pleasure to get my skinners on. Fit and finish is second to none. Finish seems to be hard as hell and all corners are nicely rounded with machining transitions almost undetectable. Most of the roll pins have been replaced with threaded allens. Additionally, there is a upper/lower tensioning screw so you can fine tune the fit. The upper/lower came with detent pins, an ambi bolt release system and dust cover assembly all factory installed. The kit also came with a proprietary barrel nut and wrench for installation. Installation instructions were well written and extremely clear. Barrel installation was a breeze just as any other AR platform. The supplied barrel wrench has a provision for a 1/2" torque wrench and the instructions call out the specific torque.

For the rest of the upper build I went with a 18.5" stainless match grade barrel from fulton armory as this was the best balance of cost/performance for my needs. The gas system is rifle length with a JP Rifles .936" adjustable gas block. Bolt is a JP enhanced 308 bolt riding in a DPMS chrome bolt carrier. The charging handle is a PRI gasbuster. Prior to ordering the barrel, I sent my bolt to Fulton Armory so they could install the barrel extension and achieve the proper headspace. I would highly recommend this to anyone building a 308 for safety reasons. Another caveat on the barrel is that the fulton armory barrel threading is just a bit too long (.030” to be exact) to accommodate the YHM quick detach suppressor flash hider. I have yet to remedy this, but my plan is to have the barrel shortened by .050” and re-crowned so the suppressor flash hider will seat on the barrel shoulder. Additionally, the upper will eventually wear an Atlas bipod, but it has been on backorder going on 3 weeks now.

For the lower, I installed a CMC trigger group again a great balance of performance/cost. I run one of these in my SBR AR. Nice, crisp break and very little overtravel. I went with a Magpul UBR stock initially but just couldn't get the cheek weld I wanted with a scope, so changed it out to a magpul PRS for the AR10. The lower also wears a Magpul MIAD grip and sports an ambi safety lever from AR15.com. Another interesting part I came across that I have been more than happy with is the JP rifles captured silent buffer spring. This is a completely contained spring/buffer combination specifically for the AR308 platform (they make one for AR15 as well). It is the correct length for carbine stocks but comes with a spacer to allow it to work with rifle length buffer tubes as well. I also installed a troy ambi mag release button to stay with the ambi theme.

For glass, I went with a Larue tactical PSR one piece quick detach mount with 20 moa built into the package and SWFA's new SS 12x42 fixed power MIL/MIL scope. The scope is another great piece for the price/performance ratio. Glass is super bright and clear in low light, reticle has been well thought out and reticle subtensions/turret adjustements are both in MILs.

First impression when you pick up the rifle is that it is pretty heavy. I haven't had it on a scale yet, so exact weight is unknown.

Range report on this sukka is what one would expect from a top notch rifle in 308. First of all let me preface this with the statement that I am no expert shooter and have very little experience with precision shooting. I shot a combination of Remington match grade 168gr, Federal match grade 168gr and Federal Fusion 150gr on my first range trip. I dialed in the scope and did a little barrel break in with the first 20 rounds. I sent a couple wet patches followed by a dry patch down the bore every round for the first ten and every three rounds for the next 9. I then shot a few 5 round groups. It was hot that day (in the 90's) with a little bit of wind (prolly 10mph cross wind) and all groups were shot from a bench on bags at 100 yards. Also want to note that these were shot un-suppressed as I just received my suppressor and haven't had a chance to shoot it yet .

All three types of ammo were shot in 5rnd groups with the Federal Match grade 168 gr holding the tightest group at .610". The Federal Fusion and Remington match grouped at .910" and .795" respectively. I am sure the rifle can do better as my eyes are old and I am not the steadiest person behind a rifle even on bags and a bench. Needless to say, I am extremely happy with the performance that was demonstrated. Next thing will be to work up a handload to see if I can improve on the group I shot with the Federal match grade.


Parts list

Mega Machine monolithic upper/lower combo
CMC trigger group
Ambi safety lever from AR15.com
Troy ambi mag release button
Magpul MIAD grip
Magpul PRS AR10 stock
JP Rifles silent captured buffer/spring

Fulton Armory Stainless Steel match grade 18.5” barrel
JP rifles .936” adjustable gas block
AR15 rifle length gas tube
JP rifles enhanced 308 bolt
DPMS bolt carrier, cam, firing pin
YHM phantom QD flash hider
PRI AR10 gasbuster charging handle
Atlas Bipod......backordered....uggggh
Larue PSR 20MOA mount
SWFA SS 12x42 fixed power Mil/Mil scope

 

[lucky4034]

Can't wait for the pics!!

 

[sgreen3]

Nice write up! Sounds like its gonna be quite the rifle.

 

[phylodog]

Looks like a very nice rifle, great job selecting the components. I've been intrigued by those JP buffer/spring assemblies but haven't had an opportunity to play with one yet. I don't want to sidetrack your thread but I'd like to hear your opinions of them, specifically for a 5.56mm rifle.

 

[sgreen3]

+1 very nice indeed!

 

[netsecurity]

Very cool 308! Thanks for sharing, and the wonderful pictures.

 

[mrfjones]

Very cool ar. I would love to have one in 308, 260 rem, 6.5 creedmore, 6.5 lapua etc.

 

[mammynun]

That's a VERY nice build! I've been looking for an Atlas bipod for my bolt gun as well, they're pretty rare these days.


But....


https://www.riflesonly.com/pro-shop/tactical-kit/atlas-bipod.html

 

[praff]

Looks like a very nice rifle, great job selecting the components. I've been intrigued by those JP buffer/spring assemblies but haven't had an opportunity to play with one yet. I don't want to sidetrack your thread but I'd like to hear your opinions of them, specifically for a 5.56mm rifle.

Really happy with the captured spring. Seems to work the same as a normal buffer/spring, but definitely quieter and no "SPROING" when shooting. There are a couple pieces on it that are plastic. I am not sure I would put one on a dedicated battle or shtf rifle as it looks like it could eventually fail, but it does seem to be a very robust design.

Also was able to get it out this weekend and do a little suppressed shooting. Impression is that it seems to be a little softer shooting suppressed. Maybe this is nothing more than perception due to less muzzle blast and noise, but not sure. Point of impact shifted a little low and left (maybe 2moa low and 1moa left), but grouping seemed to be un-affected.

Also have the Atlas bipod on the way finally, so I will report on that once i get a chance to shoot with it.

 

[tdosha]

Extremely nice build. May I ask what your approximate $$ amount was and is this a build you would suggest for someone that has never done a build?

 

[praff]

Extremely nice build. May I ask what your approximate $$ amount was and is this a build you would suggest for someone that has never done a build?

Thanks for the compliment on the build. Approximate cost for the rifle without the glass, mount or bipod is prolly in the $2800 range. That number is a guestimate, but prolly is within $300. This definitely isn't a cheap rifle to build no matter which direction you go. Stripped Lower/Upper combos are in the $600 to 1k range and bolt/carrier groups start at around $275.

As far as doing this without ever building a rifle, prolly not a huge deal if you do a couple of the things I did. First of all, the Mega upper/lower monolithic combo solves a lot of build time and hassle from the start. Most of the small parts are already installed in the lower from the factory (ambi bolt release, dust cover assembly, upper/lower tensioning device, takedown pins, trigger gard). All that is needed for the lower completion is a trigger group (mine was an assembled drop in unit), safety selector (easy to install), magazine release (easy to install), buffer tube, stock and pistol grip. Even if you don't use the Mega combo, lower assembly is not any tougher than a standard AR15. Albeit there is a caveat in that 308AR parts are not all interchangeable. There are a couple of different systems out there (Armalite AR10 vs DPMS style AR308)

For the upper, the handgard is machined as part of the upper assembly so that hurdle is already complete. I sent my bolt to Fulton Armory to have it headspace matched to my barrel assembly, so the critical gunsmithing part of this build was done at my barrel supplier. Barrel install was a breeze with the supplied instructions and barrel installation wrench. Two things you will need to complete the upper are an upper holding fixture which you can purchase or make and a torque wrench for installing the barrel nut and muzzle device. The gas tube installation into the gas block can be a little tricky to assemble, but you can purchase a gas block from JP enterprises with the tube already assembled.

None of it is really that hard if you are a bit mechanically inclined and can follow detailed directions. All of the assembly instructions/tips/pitfalls can be found on the web.

 

[tdosha]

Thanks for the info. The kit is the main reason I was thinking about going this route.
Now comes the hard part...sneaking the build pieces through the bank account without the wife noticing!

 

[cory nigra]

that is exactly my next project gun. any warnings?

 

[praff]

that is exactly my next project gun. any warnings?

No warnings other than a little sticker shock.....the $$$ add up fast. It really is one of the easier builds I have completed. I would definitely get a upper receiver vice block. I ordered one from ebay off a guy that i think is machining them himself. I think it was about $30 vs the $65 for the ones brownells and midway sells. It seems to fit just fine and meets the intended purpose.