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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


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As of 16 May 2024, Ron Allen is still making custom parts for his suppressors:

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Attached File

Ah, hence why an ARMS would still be available.

Oh and yeah, you'll get some hand slapping around here about billet lowers, but all around a nice rifle!

If you really wanted to go to the next level, get your mitts on a Nodak A1 lower and move your parts over to that.

Hmm, 99167 is the right P/N for the rails, and looking at those Mod 1 pics you sent me they still said "M4 Match (FF) RAS". It looks like they changed the engraving at some point, but I wonder when?

Everybody, check your rails! Who's got what markings and when was your junk made?

Mine was marked M4 Match FF RAS but that was before she got camo'd.

I've also seen them "5.56 M-4 MATCH RIFLE R.A.S."

I'm asking because I have a lead on one that's marked "SR-15/16 FREE FLOATING RAIL ADAPTER SYSTEM P/N 99167". and I'm uncertain I want to pull the trigger on it if the ones that get released next month are marked the old way even thought they appear to be the same part number.....

I would not mind having a NDS A1 lower with the Colt engravings done to it. The down side to getting a NDS lower is the extremely long wait time right now. I already have two lowers I have had ordered since June and July.

That's just it.  I'm going to paint my Mod1 build so it's not that big of a deal what the markings say.  It's just my anal retentive properties coming through from my retro building days and I just can't let those small details go......

Buy both and sell the one you don't want. With as rare as they are these days you shouldn't have a problem.

Shit, I'll buy one now. However, it would be for a SAM-R, so I wouldn't be able to tell you guys about it for fear of death threats.



 

On the PRi Gen III I'd wait until MidwayUSA does one of their $30 off $300 sales.  I've purchased two on that one. I still ended up with the one on the Mod 0 cheaper from that Rainier sale that you linked me, though. Thanks for that.

Quick rug pic, this rail was bought in 03/2010 from Operation Parts (It is on my teppo 458s...for now...maybe)
It has the markings "SR15/16 FREE FLOATING RAIL SYSTEM P/N 99167"

Good to know.  Thanks!

06/07 timeframe for mine -

Also what comes with the rails new in the box?  How many pieces make up the rail an collar?  Any special tools needed?  I just want to make sure I'm getting everything from the seller in this possible deal.

Just looked; mine is marked "5.56 M4 Match (FF) P/N # 99167" and the other side is marked "Knight's Armament Company, Vero Beach, FL" and what looks like a phone number.  Hard to tell after that cool-guy paint job.

 

Rail, barrel nut, collar, locking pins.



ETA: Strap wrench.
 

and instructions if they still have them.
This rail was originally on my mod1, it came from Operation parts in the fall of 2011/early 2012.
It went to a member here that was looking for rail to help complete his build.

Is there a difference between the Leupold 2.5-8x36mm TS-30 A2 and the standard Mark 4 MR/T 2.5-8x36 M2? About to order for my Mod1
Both have the Ill TMR

Thanks!

I *think* the TS-30A2 is supposed to already have the Mk 12 BDC, right? Otherwise it's just markings and BDC for elevation. One can be covered in spray paint, the other changed for what, $36?

That is my understanding as well. And I paid $36 shipped back in 2011.



 

What do you fellas make of this (the rail looks like a KAC FF RAS LONG)? I don't have much backstory on the photo, just found it on the Interwebz. The environment looks too authentic to be airsoft, but I could be wrong.

It's from the Medal of Honor Warfighter game that had a "behind the scenes" of the Navy SEALs that helped make it. The rifle is a RECCE made for the SEALs

Link to a photo of the rifle

Link to build specs

It is a recce and yes that is FF RAS long. I am making a exact clone of it, sans suppressor.

Too many damn builds out there for the KAC to go away now. Shit, there's at least 2 I want to build, Recce and Mod 1. Not really into the SAM-R, but that's the other big one out there.

Looks like that elevation turret blocks a good portion of the T-1's viewing area.

I don't think they sell that mount to civilians, so he'll be the only one that knows for sure.





 

The only thing stopping me on the SAM-R is that goddamn KAC gas block. Mk12 parts no longer seem expensive when it comes to that.



Old pic, but it makes me want another mod0 with an A1/A2.







 

Is anyone mounting one of their ARMS rings on the FF rail on the mod 1? Anyone seen this? Any adverse effects? If the rail was installed properly it shouldn't be an issue from what I gather...

One I carried 04 Iraq great rifle... Fiscus RIP,  U.S. Army KIA a year later... Great Soldier!

Finally, someone with firsthand mod0 experience.



 

I always thought the A2 butt stock too long, in the pic I'm using my M4A1 lower just for the carbine stock, most others I know using it did the same.

Stukas, glad to see you back in the forums.  Thanks for checking in with some Mod0 experience.
 

Is there any photographic evidence of Marines running the A1 grip on the mod1?  It seems the A2 is standard issue…but I can't stand the A2 grip.  Way to narrow.  Prefer the A1.  But to keep it true for a clone I don't want to slap on something that isn't used.

I completely agree, which is why mine currently wears a SOPMOD.



 

ARMS 38 SPR-PEQ-2-3 and PRI 06-SPR-PEQ rail comparison photos.

All you full-stock Mk12'ers out there need to check yourselves!



 

Nice detail; I feel perfectly comfortable saying the PRi repro sleeve is indeed clone-worthy, not that it was ever disputed mind you.



 

If they had been able to reproduce the original clamp, I'd have 3 or 4 layin' around. Those hex screws just kill it for me.



UTAH, I still maintain that a mod1 just looks "right" with an A1.

You made me do this, wheelman...




 

I didn't expect anything less.





Blame it on this guy.








 

Dammit fuckers pay attention-

"Son, I am disappoint," is what's going through that hard-charging Marine's mind right there.  Look at his face.



 

Ah yes, bridging the gap as it were.  We've got a few pics of Mod1s floating around configured in such a way but why do that when you can use the shorter SWAN S-EX Sleeve like my man RJ Miller did with his Mod1?





Marines like to bridge the gap, occasionally.











Also, I ran mine this way for a few months before I went and got all RJ Miller with mine.









Honestly, I don't think it's enough to effect your POI but I don't think it's optimal.  Seeing this Mod1 in RJ Miller's hands is quite interesting for two main reasons.  One, he was in 3rd Group, making this the first and only photo I've ever seen of an SF guy with a Mod1, and two - it's using the shorter SWAN Sleeve.





 

I got one hunting trip out of my Mod 0 with a CAR stock on it before saying

You live in FL, what's up with them midget magazines?  Also, that rig looks much better with paint and a carbine stock.  Yepyepyep.



 

MBlades early mod0 is one of the few with a CAR stock that I actually like.




I think he's trying to figure out how to get rid of that stock.



 

Limited to five round magazines when hunting deer or on public property.

Would this be acceptable for a MK12 All?
Leupold MK4 lr/t 3.5-10x40 M3 Ill. mil dot #53672

Why yes, yes it would.



 

This was discussed somewhere in the old Mk12 thread (discussion starts on p20 and goes for a few pages).  Apparently the original Ops Inc collar was designed to go with the original wheel front sight.  That front sight was a bit shorter front to back than the current version.  There was supposed to be a gap between the collar and the front sight, as the collar is supposed to sit on the step in the barrel, not the front sight.  The newer sights being a bit longer, pushed the collar forward, and it no longer sat on the barrel step, but rested on the front of the front sight.  This in turn pushed the suppressor further forward, reducing the amount of thread engagement on the muzzle brake.  As such, Ops Inc developed the shorter collar, which would again rest on the step in the barrel, not the front sight, returning the correct distance between the threads on the muzzle brake and the shoulder on the collar for correct suppressor alignment.  Bottom line, there is supposed to be a gap, al be it small, between the collar and the front sight.