My take on the Mk12 Mod1 SPR

vmpglenn

vmpglenn

Sergeant
Full Member
Minuteman
Dec 4, 2004
393
62
Fitchburg, WI
#1
Since I am an AR expert (read: I have a few tools) and since I know better than the armorers at NSWC Crane (read: I don't even know what I don't know), I thought I'd take it upon myself to precision craft (read: assemble while the kids are asleep) my interpretation of the classic SPR...

556spr_900.jpg

556spr_can_900.jpg


Upper receiver: WOA
BCG: LMT
Barrel: Superior Barrels 18" SPR contour, .223 Wylde chamber, rifle-length gas system, HardBlue finish, from a 1:7 Douglas blank
Muzzle device: Surefire flash hider
Gas block: LaRue low profile, twin set screws, 0.750" diameter
Handguard: LaRue LT15-12
Lower: Factory LMT, SOPMOD stock
Trigger: Geissele DMR 2 stage
Front BUIS: Troy
Rear BUIS: KAC 600 meter
Scope mount: LaRue SPR-S, 10MOA slope
Scope: NF 2.5-10x32 mil/mil zero stop, 3GS cattail
Suppressor: Surefire full-size

The rifle balances nicely, the scope is excellent, the trigger is smooth and crisp, and the Surefire cans are great. My go-to load will be SSA's 5.56-pressure 77gr SMK factory round.
 
#5
Re: My take on the Mk12 Mod1 SPR

Very nice! Here's my interpretation.

SPR_CLE_ST10_L.jpg


Now it wears a NF 3.5-15x50.(FastFire still piggybacked.) BBL is a CLE from a Douglas blank w/ matched bolt. Geissle SSA. LMT Enhanced Carrier (Carrier only.) Mine has a Midlength gas so I decided to slow it down a bit with the carrier and an H-Buffer. Still waiting on Form 4 approval on my Ops Inc 12th.
 
#7
Re: My take on the Mk12 Mod1 SPR

Mine? Shoots AWESOME! I've never really grouped it on paper, but on steel it seems to shoot about 1MOA with XM193. I was able to hit steel at 100yds (Or was it 200?) that was nearly edge on with it. I don't really advise this, it's one of the only things that put a gouge in that AR-500 plate. I was hoping it would flip the plate back out, but it went fully edge on.

I've got two 500ct boxes of 77gr SMK's that I need to work up a load with.
 
#8
Re: My take on the Mk12 Mod1 SPR

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Salmonaxe</div><div class="ubbcode-body">Mine? Shoots AWESOME! I've never really grouped it on paper, but on steel it seems to shoot about 1MOA with XM193. I was able to hit steel at 100yds (Or was it 200?) that was nearly edge on with it. I don't really advise this, it's one of the only things that put a gouge in that AR-500 plate. I was hoping it would flip the plate back out, but it went fully edge on.

I've got two 500ct boxes of 77gr SMK's that I need to work up a load with. </div></div>
23-23.5gr of TAC in LC brass always worked great for me for 200/300yd competitions. Cleans at 300.
 
#11
Re: My take on the Mk12 Mod1 SPR

Had a few moments (literally) to get out to the range today. I zeroed the NF 2.5-10x32 (great scope) at 100yd and set the zero stop at 5 clicks down. I also chrono'd the SSA 77gr SMK 5.56 load:

15 rounds shot, CED M2 chrono 10' from the muzzle, 60degF, 900' ASL, 29.93"HG

AVG: 2701
SD: 28
ES: 118 (!)
Hi: 2754
Lo: 2636

Corrected MV: 2710fps

I was able to concentrate for group for my last few shots with the Surefire can on (inside lower oval):

canshift.jpg


Each square on the target is 1/2". I'm satisfied this rifle can shoot MOA or better with the SSA ammo. I, however, cannot do so when in a hurry...

As you can see, POI shift with the can attached is right at 2.5" at 100 yards, straight down. This is easy enough to account for, so I'm good.

I have a Tubbs flat wire extended action spring installed in the carbine receiver extension, along with a standard H buffer. With the SSA ammo, the rifle shot very softly, and ejection was at my 4 o'clock, about 8' away. With the can attached, ejection was at my 2 o'clock, about 5' away.

No malfunctions of any kind, although I did only shoot a single PMAG (30 rounds) of ammo, so I wouldn't read anything into that. With the Surefire can attached, this rifle shoots like a .22 -- recoil, noise signature, etc. Plus, there's almost no blowback because of the rifle length gas system and the reflex design of the Surefire can. Yeah, the insides get a bit dirty, but I'm not wreathed in gas like I am when shooting my SBRs suppressed.
 
#15
Re: My take on the Mk12 Mod1 SPR

Very nice rifles gentlemen!

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: decodeddiesel</div><div class="ubbcode-body">Good stuff guys. I really need to get my tail in gear on a MK12 build. With the BCM barrels and uppers available, there is no better time. </div></div>

Indeed. Others may disagree, but I feel my SPR is by far the most versatile weapon in my arsenal. I just reinvented mine with a Noveske barrel and DD Lite 12.0, and couldn't be happier...

-matt
 
#18
Re: My take on the Mk12 Mod1 SPR

I just bought that same barrel from Superior Barrels..My build is going to be SPR'ish.. Probably not spec due to high cost parts and hard to get parts(KAC rail and OPS brake)..

It seems like that is a big PoI shift with the can on.. I would imagine its due to the threads not being cut, centered to the bore??
 
#20
Re: My take on the Mk12 Mod1 SPR

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: JSTARSZ</div><div class="ubbcode-body">I like it and your detailed explanation of how it came to be...it is always nice to keep a sense of humor</div></div>
+1

A man's got to know his limitations...or lack thereof in this case!

Very nice sticks guys (read: I've got to get one of these)!!
 
#21
Re: My take on the Mk12 Mod1 SPR

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Dirknar</div><div class="ubbcode-body">I just bought that same barrel from Superior Barrels..My build is going to be SPR'ish.. Probably not spec due to high cost parts and hard to get parts(KAC rail and OPS brake)..

It seems like that is a big PoI shift with the can on.. I would imagine its due to the threads not being cut, centered to the bore?? </div></div>

I agree the POI shift is probably caused by the barrel threading. However, since the shift is elevation only, it will be easy to compensate. My inclination is to shoot mostly suppressed anyway since the can/rifle combo has such minimal blowback.
 
#24
Re: My take on the Mk12 Mod1 SPR

Very nice lookind build, kinda OT but how does those suppressors attach on the surefire set-up without having to remove the flash hider? I'm kinda new at this so please excuse me if this is a silly question, thanks
 
#25
Re: My take on the Mk12 Mod1 SPR

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: dk05r1</div><div class="ubbcode-body">Very nice lookind build, kinda OT but how does those suppressors attach on the surefire set-up without having to remove the flash hider? I'm kinda new at this so please excuse me if this is a silly question, thanks </div></div>

The suppressor mounts to the flash hider. There is a pin inside the can that mates to a groove on the underside of the flash hider, and the ring at the rear of the can rotates to bear against the rear shoulder of the flash hider. A spring-loaded lever engages teeth on the ring to lock it down firmly. The whole thing is rock solid.
 
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