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The following parts lists and substitution parts was compiled by lancecriminal86 over the course of a LOT of research. Read up and pay attention!

Below are the 100% .mil-spec parts lists to build a true SPR or Mk12 clone. Some of these parts are no longer manufactured and will require much effort and money to locate through forums and online brokers. Keep in mind the rifles were built off donor M16A1s, hence the prevalent A1 parts in the lower receivers and the BCGs. They were also first configured using parts available from 1998-2004, and most are inferior in some ways to newer designs. If this bothers you too much, STOP NOW.

The rifles were issued as a kit in a Pelican 1700 case with cutouts. The kits included the rifle with suppressor, optic, bipod, an Eagle TAS-1 UMSS sling (unobtanium and also absolute crap), with a Dewey 1-piece cleaning rod plus Otis cleaning kit, and a cutout for magazines. An operator's manual was also included, however these have not been officially released for public consumption. However, the manuals are out there, and some companies building Mk12 uppers include one. Whether these are official .mil operator's manuals or specially made is currently unclear as the manual itself still contains language that it is not for distribution.

- Alternate .mil-spec parts due to NFA, NLA parts, or changes in name/markings for current production in [brackets]

- Extra notes about parts or availability are in (parenthesis)

LOWER
Lower receivers were standard across the SPR/Mk12 variants and the only variations would be between grips, stocks, and buffers. Most were marked either Colt or GM Hydramatic. All other parts were the same in regards to the lower parts. One caveat is the trigger, as the program originally selected the Knight's Armament 2-stage Full Auto Match trigger. Later on, some issues regarding negligent discharges occurred, and Geissele SSF triggers ultimately found their way into the Mk12 family. Whether 100% of all Mk12s eventually received the Geissele trigger isn't clear, so either is acceptable.

• Lower: M16A1 pattern [Nodak Spud NDSA1 or 80% re-profiled/finished/engraved]
• Trigger: Knight's 2-Stage Full Auto Match Trigger or Geissele SSF [KAC semi-auto Match or Geissele SSA/SSA-E]
• Grip: A1, A2, ERGO Original
• Stock: Originally issued with A1 stocks, both solid D and trapdoor E types; as A1 stocks dwindled, A2 were used; ModH rifles rebuilt with Ace SOCOM stocks
• Small parts: Standard M16A1 parts
  
  

UPPER
The upper receivers, which ultimately differentiate the four variants of the Mk12, have the most variation between each other.


Early SPR/Mod0

• Upper: Colt, Diemaco, or Armalite marked, flat top, M4 feed-ramps
• Barrel: Douglas 416r SS, 18" SPR contour, 1/7 twist, flats milled for PRi FSB (Compass Lake, Centurion Arms, High Caliber Sales, and PRi can all supply barrels that meet the appropriate spec minus FSB flats)
• BCG: Colt M-16
• Handguard: Precision Reflex Gen I carbon fiber free-float Handguard, rifle length (identified by button-head screws and one vent hole near barrel nut on lower half; no heat shields)
• A.R.M.S. #38 SPR MOD Sleeve (either the PEQ version or with uneven spacing on the front  but not the full 1913 railed version)
• FSB: PRi early folding front sight base and gas manifold, set-screw, with elevation wheel
• Charging handle: PRi Gas Buster M-84 with military latch
• Muzzle device: OPS Inc 12th Model brake/collar, and 12th Model suppressor [Allen Engineering AEM5 and brake/collar]
• Rear iron sight: A.R.M.S. #40
• Scope rings: A.R.M.S. #22 Medium rings, #22 Tactical Ring Cap and #22 Tactical Ring Rail (rings should not include "lever-stop" hump as produced later by A.R.M.S.)
• Optic: Leupold Vari-X III 3.5-10x40mm LR, M3 turrets, illuminated Mil-Dot reticle (use .308 turret) [Leupold LR/T 3.5-10x40 LR, M3 turrets, Illuminated Mil-Dot reticle]
• Bipod: Versa-Pod with A.R.M.S. #42, or a Harris with A.R.M.S. #32 (Versa-Pod far inferior to Harris)

Late Mod0

• Upper: Colt or Diemaco marked, flat top, M4 feed-ramps
• Barrel: Douglas 416r SS, 18" SPR contour, 1/7 twist, flats milled for PRi FSB (Compass Lake, Centurion Arms, High Caliber Sales, and PRi can all supply barrels that meet the appropriate spec minus FSB flats)
• BCG: Colt M-16.
• Handguard: Precision Reflex Gen III carbon fiber free-float handguard, rifle length
• A.R.M.S. #38 SPR-PEQ-2-3 Sleeve
• FSB: PRi folding FSB, set-screw, .750 (original production had PRi's full address engraved on sight tower; those engraved with "PRi USA" are later manufacture)
• Charging handle: PRi Gas Buster M-84 with military latch
• Muzzle device: OPS Inc. 12th Model brake/collar, and 12th Model suppressor [Allen Engineering AEM5 and brake/collar]
• Rear iron sight: A.R.M.S. #40
• Scope Rings: A.R.M.S. #22 Medium rings (rings should not include "lever-stop" hump as produced later by A.R.M.S.)
• Optic: Leupold 3-9x36mm TS-30, Mk4 MR/T 2.5-8x36mm TS-30A2, M2 turrets with Mk262 BDC, illuminated TMR reticle
• Bipod: Harris with either A.R.M.S. #32 or KAC RAS bipod adapter

SPR/A, SPR/B, Mod1

• Upper: Colt or Diemaco marked, flat top, M4 feed-ramps
• Barrel: Douglas 416r SS, 18" SPR contour, 1/7 twist, flats milled for PRi FSB (Compass Lake, Centurion Arms, High Caliber Sales, and PRi can all supply barrels that meet the appropriate spec minus FSB flats)
• BCG: Colt M-16
• Handguard: Knight's Armament M4 Match FF RAS, rifle length (now called the SR15/16 Match FF RAS)
• Gas block: NSWC Crane pattern (Badger Ordnance parkerized/NSN version is correct, has open front of gas tube hole)
• Charging handle: PRi Gas Buster M-84 with military latch
• Muzzle device: OPS Inc. 12th Model brake/collar, and 12th Model suppressor [Allen Engineering AEM5 and brake/collar]
• Scope rings: A.R.M.S. #22 High rings (A.R.M.S. rings should not include "lever-stop" hump as produced later by A.R.M.S.)
• Optic: Leupold Mk4 MR/T 2.5-8x36mm TS-30A2, M2 turrets with Mk262 BDC, illuminated TMR reticle or NightForce 2.5-10x24 (optionally with NightForce rings)
• Bipod: Harris with KAC RAS bipod adapter (BRM-S, A.R.M.S. #32 could still optionally be used)

ModH, Mod "Holland"

• Upper: Colt or Diemaco marked, flat top, M4 feed-ramps
• Barrel: Noveske 16" Recon, mid-length gas system, profiled for OPS Inc. 12th Model brake/collar (will require aftermarket contouring of most barrels)
• BCG: Colt M-16
• Handguard: Precision Reflex Gen III carbon fiber free-float handguard, FDE, rifle length
• Charging handle: PRi Gas Buster M-84 with military latch
• Muzzle Device: OPS. Inc. 12th Model brake/collar, and 12th Model suppressor [Allen Engineering AEM5 and brake/collar]
• Scope Rings: A.R.M.S. #22 Medium rings on PRi recce rail (rings should not include "lever-stop" hump as produced later by A.R.M.S.) or LaRue LT-104 SPR mount
• Optic: Leupold 3-9x36mm TS-30, Mk4 MR/T 2.5-8x36mm TS-30A2, M2 turrets with Mk262 BDC, illuminated TMR reticle, Leupold Vari-X III 3.5-10x40mm LR, M3 turrets, illuminated Mil-Dot reticle (use .308 turret) [Leupold LR/T 3.5-10x40mm LR, M3 turrets, illuminated Mil-Dot reticle]; S&B Short-Dot
• Bipod: Harris with either A.R.M.S. #32 or KAC RAS bipod adapter
• Iron sights: (apparently PRI were supplied but never used)
  
  

In the Wild
Naturally, once these rifles were issued to units, operators and even Marines used various non-issued parts. Here is a short summary of what has been seen:

Early SPR/Mod0:
Both Leupold 3.5-10x40mm and 3-9x36mm scopes have been used. Many have had carbine stocks like the old CAR-style, enhanced M4, SOPMOD Gen I, or even the Tactical DuoStock swapped on.

Mod1:
One 3rd SFG-issued rifle pictured with SSgt Robert J. Miller (MoH recipient) used an A.R.M.S #36 S-EX 5.56mm rail, and a Leupold M3X 10x fixed-power scope, possibly pulled from an M-24 or SR-25 rifle. Another has been seen with a Magpul PRS, LaRue mount, and a Premier Reticles 3-15x used by an AMU shooter, and a similar rifle was pictured on a FOB in a very posed-looking photo. Further, a USMC-issued Mod1 was seen using #22 Medium rings instead of High rings, and a LaRue mount has been spotted as well. Grips have varied from the usual A1, A2, and ERGO, and at least one Magpul MIAD has been used. As with the Mod0s, carbine stocks like the SOPMOD and M4 have been used on Mod1s.

ModH:
The Mod "Holland" was already a small-batch configuration, but even as soon as they were issued to 5th SFG units, some Ace SOCOM stocks were replaced with Magpul ACS and CTR stocks. Optics are basically anything existing in the unit's inventory, from S&B ShortDots still in the system, the 3-9x and 3.5-10x Leupold scopes from earlier Mod0s, and there's even a photo of an ELCAN on a Mod1 floating around. No non-magnified optics like EOTechs or regular Aimpoint M2/M4s, but Micros have been seen on offset mounts. Backup iron sights, as a whole, were almost entirely left unmounted. Grips were again the same usual selection.

Parts Alternatives for Clone Building
Many parts are rare, expensive, and/or both. Despite this, there are some alternatives to a 100% pure clone that will still provide the same visual look and performance. While not a museum-grade clone, most would be hard-pressed to discern the difference. Just know there are those of us out there that will haze and peer-pressure you into further moving your build towards a true clone.

Barrel:
Popular options are the White Oak Armament SPR barrel (rifle gas), BCM's SPR barrel, Rainier's Match and Ultramatch offerings (ensure it's the SPR contour with 12th Model profile), Ballistic Advantage's SPR barrel. Compass Lake Engineering can also spin a Mk12 profiled barrel with a Criterion chrome-lined blank, or even a Krieger, which was one of the original contenders for the program. The DPMS Mk12 barrels are NOT properly profiled for a clone.

Optics & Rings:
In the case of the Leupold 3-9x or 3.5-10x, it's generally okay to go for a non-illuminated version of either, sometimes with M1 or other turrets and reticles. As far as the NightForce scope, the 2.5-10x24mm is not generally released to the public anymore (with one recent exception through Sniper's Hide), so many use the 32mm or even 42mm versions with the #22 High rings. As for the rings, any of the recent produced A.R.M.S. #22s with the lever-stop humps are functionally the same, the desire for non-lever-stops is purely aesthetic when going for the most authentic look. As LaRue LT-104s have been seen in use, it is justifiable to use one depending on whether you have a specific rifle you want to copy, or even just if you absolutely cannot acquire #22 High rings.

A.R.M.S. #38 SWAN Sleeve:
The #38 family of sleeves are no longer available. Finding them secondhand usually cost $250-$300 easy, more for rarer early variants. Fortunately, PRi's copies of the sleeves look and function almost identically, with minor visual differences. PRi and other builders supply these currently for complete Mod0 builds.

FSB:
While the set-screw version of PRi's FSB is spec, most use the cross-bolt, clamp-style version. They are extremely robust, and when aligned and torqued, have been shown to hold strong enough that you'll probably shear your barrel extension pin or upper before it budges. This is mainly how Mod0 uppers are supplied by most vendors, including PRi themselves.

Suppressor, Brake/Collar:
Diverging from the OPS Inc. or AEM brake and collar will get you MAJOR flak. Trust me, I've been running an AAC SPR/M4 for years now and it took a LONG time to not get clubbed every time I posted it. The Allen Engineering AEM5 is basically the current production of the OPS Inc. 12th Model, as they were originally made by Ron Allen and his team in the first place. Only minor differences separate original OPS Inc. cans from AE cans, and these are only obvious to trained eyes.

As far as the rest, you can swap Colt parts out for any other .mil-spec parts, like BCM, DD, CMT, etc. Any billet uppers/lowers, funky BCG coatings, extended bolt releases, etc. are extremely frowned upon. Remember, once you start going down the path of building a "better" rifle rather than what was spec, you're quickly beyond clone territory and would have been better off building a custom 16" or 20" rifle. Cloning is generally viewed as all-in or not at all.

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Complete Mk12 Mod0 / Mod1 Uppers
Bravo Company Manufacturing
High Caliber Sales
Precision Reflex Inc.

Specific Mk12 Tech
Augee's side-by-side comparison of the original ARMS SWAN Sleeve and PRI reproduction PEQ Sleeves: bottom of p136
KOBK's side-by-side comparison of PRI Gen I, II, and III handguards, and Gen I and Gen II FSBs, and SWANs: middle of p137
Augee's Mod1 gas block tech: top half of p357
Glass1's Early Mod0 photo breakdown: middle of p449
tamboi's Leupold Vari-X, TS30, and TS30A2 scope history/lineage, and part numbers, p.792

Attached File

Does anyone have one of those fake AEM cans that they might not need anymore? Shoot me a message. Thanks

Teardrop or round forward assist?

Are you cloning a specific gun or just asking what people prefer?

The only round assist I have came on my factory KAC .300B upper. I just love the look of the old-school teardrop pawl.

Just seeing what the general consensus is. Doing a mod 1.

Round because it's either in a parts kit or usually already comes with the upper.

I personally like round on the Mod 1, but 100% say tear drop for a 0

Early or later round forward assist?

I'm rehashing shit from years ago so hang onto your panties...

Are there any in the wild pics of RMRs being on top of mod 1s or even 0s?

I can't confidently say RMR, but we do know Docters or maaaaybe old JPoints. RMR would have to be a more recent photo of the ones guys dug out or held onto.

Sorry, I need to stop using RMR as a generic catch all for reflex sights lol

I'm assuming they were only seen on TRC/TRR as opposed to something like an LT788

Seen em a few different ways, mainly on Mod 1s. I'll take a pass at the collection here.

There was at least one on a scope mounting system similar to the LT788.  A member here carried it.

Picked up an old (I hope) Docter used off Euro optic.  

Now to figure out WTF to mount it on...
I don't understand why there's not more 30mm tube mounts.

Edit - fuck it, ordered a 788

It wasn’t my favorite mount, but I used the GG&G mount for putting a Docter on my -12 during 2008-2010 deployments.  They can still be purchased at GG&G.  Used Larue afterwards since they dowel posts and were also 34mm.  

During 2011-2012, we used the RMR on the mk11’s and 12’s in Larue mounts.  I have of my mk12 clones built in my final deployment configuration with it.  They were RM05’s pulled off of m240 optics in the armory.  T1’s were also used too, all in Larue mounts.  That mk12 would ruffle feathers of some of the purists in this thread.

I have one sitting in the bin, was gonna put it in the ee lt788

Good info.

I personally tend to think the amount of people who would be upset to see "non spec" stuff in actual Mil use on Mk12s number rather few.  Ruffle away.

Post up the pics if you have them, screw the purists.

This is why I build what I build.  Seen enough pictures of in use stuff to realize anything goes basically.

The Late Mod 0 that also had SPR optics on it:


Late 0 with offset Docter in ring mount


Augee's pic of one on a TRR



Slightly off what you asked, but a T-1 and M2010 optic:


Another offset T1 I think

I build off of plausibility quite a bit as far accessories go. But I'm anal about the base rifles themselves... At least for my own builds.

JPoints were in a 50/50 mix with the Docters in my experience.  Different mounting patterns dictated which mount you could use.  JP had a mount at the time which was the best in my opinion.  The GG&G I had for Docters always had me concerned since the mounting screws for the sight itself were the only thing securing the sight.  No dowel posts.  But it’s what I had on one deployment.  JPoints and RMR for others, and T1’s at the final.  Some guys used the special ring for Larue scope mounts that were around.  I’m a lefty so something wasn’t working right with the one mount I was playing with trying to put the adapter on the left side.  Whatever the issue was, I abandoned that option.

Best scope I had for the mk12 was when the SWFA 3-9x FFP hit the market.  That was the winner at the time since the only way to get FFP was the heavier stuff in inventory.  The SWFA kept the rifle lean.  I used it in Nightforce rings.  It also meant keeping the 30mm mounts for red dots...

I can’t post photos here like I can on the Hide, so if someone wants to host them I’ll email a few when I get home.

Sending you an email.  I'll post them.

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Figured it had to have happened somewhere over the years, surprised it took this long for a pic to float up.

I'm trying to wrap my head around the lower.  Something ain't jiving

What rail is that?

Almost looks like a URX 2.

Plot twist: Daniel Defense somehow got their "Mk12" uppers in the right hands and now them shits is cloney.

A Premier on a 12?

these are the issued rifle pics from @j-dubya1 ? that OG 99051 is a work of art
awesome intel and feedback J-dubya1.
the mk12 history is fascinating




What is this? Surefire suppressor?

Rifles on the floor are exact clones of deployment rifles.  Premier came off of a new m110 when they made it down to the team.  I had purchased a Premier for myself when they first came out in ‘09, so I was already familiar with them.  A teammate with his 110 wanted to use a Schmidt, so I took his Premier and gave him a Schmidt off one of the overstock mk11’s.  Made the 12 too hefty in my opinion.  Those scope rings alone are one whole pound...  but it worked great for how it was employed.  All that weight let the rifle just sit when fired.  Like a .22.  Same concept of how the PRS guys have gone now with making rifles heavier than normal.  

I can’t paint the spec clone...too many hard to find parts on it that I probably shouldn’t cover up.  

If anyone has an original JP mount, I’m hunting one for another 12 clone.  The mounts from the past eight years or so are a different design.

As for that “different” mk12 picture, that is indeed a Surefire and URX rail.  Unknown members to me, they are green side best I can tell.

This is a good doctor mount for a ring mount, I grabbed one for the nsw recce and the older doctor looks great on it Burris 30mm ring mount

After seeing the pics on this page, I need to find a few pmag 20 rounders that are straight. both black and fde.

Got my Mk12 Mod 1 put together about a  month ago.  It is not, nor will it be an exact clone due to the scope I run (I'm not interested or wanting to pony up the funds to find a correct clone scope right now).  I generally build for function over fashion, but I love the MK12 platform.  I had orginal done a Mod 0 but sold it a few years ago here in the EE.  This time with the panic and cost, I went with the Mod 1.  I really like the weight difference with the Mod 1, but still miss the Mod 0 I had put together.  

It seems doing this a second time around it was easier, but still fulfilling.  Between reading on here and knowing what parts to hunt a find, it truly felt i was become a more experienced builder.

Lower:

Aero Precision ( I wanted a tension screw for the receivers).
Geissele High Speed match Trigger with the DMR springs.  Have it adjusted to approximately a .5 pound break on the 2nd Stage.
CMMG LPK
Vltor A5 buffer kit (something new to try and so far the recoil feels like a rifle length buffer)
B5 SOPMOD (Was with the orginal Emod stock)

Upper:
Poverty Pony
BCM gas block
BCM Bolt carrier
Compass Lake Engineering MK12 barrel on a Douglas Blank.  Had the CLE chambering and so far I really like it, though it is tight for steel case stuff.
CLE matching Bolt
Allens Engineering Brake and Collar.  Sad to see OPs Inc out of biusness.
Harris Bi-Pod with Knights armament mount
KAS MK12 rail from Titusville, FL (Igraduated from Titusville HS in 2002 so that rail is a bit special)
Vortex Viper 5-15x Mil-dots.  Midway USA run.  AMD 20MOA mount.

Next to get is a Pelican case and the correct BUIS sights.

Shoots incredibly if I do my part.  Been out of the game for so long it is hard to get my old groupings back.







ETA: Where is the best place to get an AE5 suppressor right now?  Want one severly, and will be my first suppressor to get.

with all the good info on 30mm ring mounts popping up it got me wondering:
what mount to attach the Docter sight to the A.R.M.S. #22TRR ??

Everywhere is sold out right now, if you call Capital Armory you can purchase one now and be placed on backorder. That is what I did to "get ahead of the line"

I'm kind of thinking you're right.

I don't think there's a URX that long for a 15, it very well could be a DD rail...

Long out of production, but it’s a rifle-length URX.  You can see the front sight push button in the picture.  Daniel Defense has a different hole pattern.

Edit - I’ve got one of those rails on the shelf and can get a photo later today.

Yeah I was only kidding about that thing being a DD upper; I just wanted to stir the pot a little, lol. I do see the push-button for the front sight, which makes this a unicorn upper since the rifle-length URX II ain't in production anymore. I'd love to have that rail for a build.

ETA: When did KAC start integrating QD sockets into their rails? I feel like the URXs didn't get those until 3.1 series.

ETA: Never mind, Outrider answered my question.

Rifle length URX II is 12.5" if I recall. I had one on the recce for a little bit. On/off topic picture.

Such a sweet setup.

I want a rifle length URX 2 in the worst way.  I didn't even realize it was a production item.  I thought it was only on complete rifles.

I want it for this hog....

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The QD sockets are present in all the URX 2 rails.  The original URX did not have the built in front sight or sockets.  

I’ve had my URX for ten years now, and while it only sits on the shelf these days, the only way I’d give it up is for a FF RAS with the “M4 Sniper” marking instead of “M4 Match”.  If anyone wants a rifle URX and has the M4 Sniper RAS, let’s talk!

AEM5s in stock at Capitol Armory

Wow these went up in price.

Not by a whole lot compared to when I bought mine in 2019 through HCS - $675 iirc

I grabbed mine from BPT Mid summer 2019 for $520

Purchased from eSilencers for $625 in May 2020.