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6.5 Grendel build inspired by the military SPR Mk12 - Printable Version

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6.5 Grendel build inspired by the military SPR Mk12 - spr mk12 mod 0 - 09-10-2020

And the upper is finished:

[Image: Grendel_(39).JPG?width=1920&height=1080&fit=bounds]

[Image: Grendel_(38).JPG?width=1920&height=1080&fit=bounds]

[Image: Grendel_(41).JPG?width=1920&height=1080&fit=bounds]

Onward to the lower...........

6.5 Grendel build inspired by the military SPR Mk12 - danm - 09-10-2020

Thumbs up man!

6.5 Grendel build inspired by the military SPR Mk12 - biodsl - 09-11-2020

I can't wait. Gonna be a beauty.

6.5 Grendel build inspired by the military SPR Mk12 - drewthebrave - 09-11-2020

This is a great thread, thanks for taking the time to detail each step with some high quality photos. I usually just blow through the whole assembly in one sitting to get to the range ASAP, where I can (hopefully) verify that I didn't screw something up! Cool
Your patient approach is much more methodical than mine, and your attention to detail is admirable.

6.5 Grendel build inspired by the military SPR Mk12 - spr mk12 mod 0 - 09-11-2020

Thanks!

Quote:...........I usually just blow through the whole assembly in one sitting to get to the range ASAP..........


ME TOO! But building this has been fun project and knowing I'm taking close up photos makes me slow down and try to do a careful job.

Started on the lower receiver. I really like the Geissele magazine release button. Very classy all checkered and with a beveled edge:

[Image: Grendel_(52).JPG?width=1920&height=1080&fit=bounds]

I was going to also use Geissele's fancy lad ULTRA PRECISION 5 AXIS TRIGGER GUARD but I forgot to send it in along with the rest of the parts to be Cerakoted. So I plugged in an FDE Magpul:

[Image: Grendel_(44).JPG?width=1920&height=1080&fit=bounds]

I also used the really nicely made Geissele magazine catch. It's nicer than any GI style parts kit piece I've see so far.

Oh, and that huge Geissele Maritime bolt catch......well......we'll see. That's the good thing about building an AR. Anything I put on, I can take off:

[Image: Grendel_(43).JPG?width=1920&height=1080&fit=bounds]

I wanted to show the inexpensive specialty tools used to install these parts:

[Image: Grendel_(53).JPG?width=1920&height=1080&fit=bounds]

They really help in doing a clean installation without scratching up the receiver. I don't mind a scratch from field use but I think a fresh build should be clean.....knock on wood. So far so good on this one.

6.5 Grendel build inspired by the military SPR Mk12 - spr mk12 mod 0 - 09-13-2020

I've been using mil spec style triggers from Geissele, their SSA/E enhanced. I believe they are even approved by the US military amd they break cleanly at about 3.5 pounds:

[Image: Grendel_(60).JPG?width=1920&height=1080&fit=bounds]

For this build I decided to try something different, the Triggertech Adaptable 2-stage:

[Image: Grendel_(45).JPG?width=1920&height=1080&fit=bounds]

And their safety selector too. It can be setup for right hand or bilateral use and either a 45 or 90 degree throw:

[Image: Grendel_(54).JPG?width=1920&height=1080&fit=bounds]

Their safety detent is a different style in that it uses a ball tip and a large base. That allows the safety to be removed without taking the pistol grip off and leaves the detent in place:

[Image: Grendel_(50).JPG?width=1920&height=1080&fit=bounds]

6.5 Grendel build inspired by the military SPR Mk12 - spr mk12 mod 0 - 09-13-2020

The Triggertech instructions said the safety needs to be installed first and that starts with the Magpul grip, V Seven titanium screw, detent and spring:

[Image: Grendel_(55).JPG?width=1920&height=1080&fit=bounds]

The cartridge style trigger went in easily but that's one complicated looking piece of kit compared to the GI style Geissele trigger. At least Triggertech says it's designed to run without lubrication so maybe it won't be a malfunction prone dirt magnet:

[Image: Grendel_(47).JPG?width=1920&height=1080&fit=bounds]

Here's the trigger, safety and grip installed:

[Image: Grendel_(48).JPG?width=1920&height=1080&fit=bounds]

[Image: Grendel_(49).JPG?width=1920&height=1080&fit=bounds]

The recoil spring and buffer system is next......

6.5 Grendel build inspired by the military SPR Mk12 - jasper2408 - 09-13-2020

I also use Triggertech in my AR lower. Absolutely no creep. I have never had to clean my trigger with any solvents with at least 500 rounds shot thru it with various uppers. I just clean what I can get to with a dry rag and off we go. Never a malfunction so far. Also I have never had mine come loose once I tightened the snug screws. No loctite had to be used to keep them tight.

Also, this is one nice looking build so far. That camo is awesome. Great job. Smile

6.5 Grendel build inspired by the military SPR Mk12 - spr mk12 mod 0 - 09-13-2020

Thanks. That's good to know about the trigger. The trigger pull sure feels nice. I have it set at 3.5 pounds for now.

6.5 Grendel build inspired by the military SPR Mk12 - spr mk12 mod 0 - 09-14-2020

I'm starting out with a fixed Magpul rifle buttstock:

[Image: Grendel_(56).JPG?width=1920&height=1080&fit=bounds]

For the buffer and spring I'm trying JP's Silent Captured System:

[Image: Grendel_(57).JPG?width=1920&height=1080&fit=bounds]

JP's website flow chart suggests an H2 buffer setup:

[Image: Grendel_(58).JPG?width=1920&height=1080&fit=bounds]

There are 5 different spring rates. I thought I'd start out with the heaviest, fire a single round and see if the bolt lock back on the empty mag. If not, then go with the next lightest spring and repeat............that's my theory anyway:

[Image: Grendel_(59).JPG?width=1920&height=1080&fit=bounds]

6.5 Grendel build inspired by the military SPR Mk12 - spr mk12 mod 0 - 09-14-2020

If all the above fails my fall back plan is the good old AR rifle buffer..........

[Image: Grendel_(66).JPG?width=1920&height=1080&fit=bounds]

..........and buffer spring. This one is JP's Custom Operating Spring:

[Image: Grendel_(67).JPG?width=1920&height=1080&fit=bounds]

It's centerless ground and polished:

[Image: Grendel_(65).JPG?width=1920&height=1080&fit=bounds]

Here's the lower. I guess I got a little "fancy lad" with the polished trigger. It seemed like a good idea at the time:

[Image: Grendel_(51).JPG?width=1920&height=1080&fit=bounds]

Time to put it together and get it on the scale. Then it will be time for a decision on optics. I'll share some pictures of what I've got so far...........

6.5 Grendel build inspired by the military SPR Mk12 - danm - 09-15-2020

Optics are an arduous decision.... My 18" G wears a 2.5-10 PST in typical DMR fashion. I'm about 90% sure I'm gonna do the 3-15 PST 2 on my 6arc... but that leaves 10% for other options Smile

6.5 Grendel build inspired by the military SPR Mk12 - spr mk12 mod 0 - 09-15-2020

Optics are indeed an arduous decision. I've got a couple to share but I'm still not sold on either one for this particular rifle.

But first here's the finished rifle. I couldn't go outside and try to find a cool looking background. The wildfire smoke here in Western Oregon is horrible right now.

Here she is sitting on my workbench:

[Image: FSCN9281.JPG?width=1920&height=1080&fit=bounds]

[Image: Grendel_(77).JPG?width=1920&height=1080&fit=bounds]

Without the bipod the rifle weighs 7 lbs. 4 oz. If I switch to an ACE or Hogue rifle buttstock I could knock that down to a hair over 7 lbs. With a steel barrel of similar profile it would weigh closer to 8 lbs. 5 oz.

6.5 Grendel build inspired by the military SPR Mk12 - drewthebrave - 09-15-2020

I honestly don't mind a few extra ounces in the stock - it's the front end where I tend to prefer saving weight. Of course, optic selection could change the feel quite a bit. Can't wait to see what you pick.

6.5 Grendel build inspired by the military SPR Mk12 - danm - 09-15-2020

Such a good looking rifle! I'm with you on the smoke, actually worse here... all the smoke from WA and OR is settling in our valley... Lewiston,Clarkston...

6.5 Grendel build inspired by the military SPR Mk12 - Huckleberry75 - 09-16-2020

danm Wrote:Such a good looking rifle! I'm with you on the smoke, actually worse here... all the smoke from WA and OR is settling in our valley... Lewiston,Clarkston...

That's not good. I am headed there in a couple of weeks with an OTC bull tag. Hope it clears up, or the elk all might expire from lung cancer before I get there and make one of them expire from a dramatic drop in his blood pressure. Cool

6.5 Grendel build inspired by the military SPR Mk12 - spr mk12 mod 0 - 09-16-2020

The color in the pictures went a bit greyish on part of the rifle I guess from taking the picture indoors with a flash.

Optics. I know there are a zillion ways to go and no two people will probably think the same way.......but here goes.

My first thought was to use the Nightforce NX8 1-8X. I replaced a Leupold VX6 1-6X MultiGun with one and liked it much better. On 1X with illuminated reticle it is almost as fast as an Aimpoint Micro T-2 red dot. I wish it was American made but at least it's not Chicom:

[Image: Grendel_(68).JPG?width=1920&height=1080&fit=bounds]

I want a mount that I can remove without tools. That's a "personal problem" of mine. My go to mount has been the Laure SPR. Now in the LT204 C.A.N. style. I like the gusset they put under the "diving board" part of the mount. It just looks beefier to me:

[Image: Grendel_(70).JPG?width=1920&height=1080&fit=bounds]

[Image: Grendel_(72).JPG?width=1920&height=1080&fit=bounds]

I know the military is going with a low power variable optic for their DMR's but in the back of my mind I kept thinking about more glass for the Grendel. I stumbled on this ring/optic mount for the LT204 on the Larue site and it got me to thinking (usually an expensive proposition for me):

[Image: Grendel_(75).JPG?width=1920&height=1080&fit=bounds]

I know mounting a reflex sight for CQB along with an optic is not new but it is to me........I'm old! I've been using either an Aimpoint T1/2 or a LPVO but not a scope and a red dot. But this ring/mount for the super small red dots is something I just have to try.

6.5 Grendel build inspired by the military SPR Mk12 - spr mk12 mod 0 - 09-16-2020

Sure enough this turned into an expensive proposition. First with the Noblex-Docter Optics mini red dot sight:

[Image: Grendel_(78a).JPG?width=1920&height=1080&fit=bounds]

Here's everything it comes with:

[Image: Grendel_(79a).JPG?width=1920&height=1080&fit=bounds]

The thing is so small..........

[Image: Grendel_(80a).JPG?width=1920&height=1080&fit=bounds]

...........and light:

[Image: Grendel_(81a).JPG?width=1920&height=1080&fit=bounds]

And how can you not like it when it's got a owl inscribed on one side.

6.5 Grendel build inspired by the military SPR Mk12 - spr mk12 mod 0 - 09-16-2020

Then I sprang for this Nightforce NX8 2.5-20x50 scope:

[Image: Grendel_(69).JPG?width=1920&height=1080&fit=bounds]

When I hold it, it just seems heavier than I'd like for this rifle. It's 28.6 oz. which I don't believe is all that heavy for a 20X scope.

But, I'm having second thoughts..............

6.5 Grendel build inspired by the military SPR Mk12 - biodsl - 09-16-2020

I feel your pain but you're on your own. People can suggest but optics are a difficult choice. I have several but my favorite is an old Vortex 2.5-10 44mm SFP PST. Many wouldn't walk across the street for this old thing, but I love it. (To me) the perfect combination of weight and function for what I do.

The rifle looks stellar.