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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

Looks like short collar to me

I agree.  Looks like the collar step is too far back towards gas port.  Ask for measurements from the thread shoulder before you buy

Damn that looks sexy. I dig it black, I'd leave it but that's me. I came across one of those Knights top rails with integrated rear buis at a gun show for $150...but didn't know what it would be clone correct on so I didn't get it

Of all the MK12 options that's my favorite look.  Well done.  The sopmod doesn't help that much.

That is just frickin' badass

I think I’m gonna quit fighting it and give in to the Mod 0 clone game. It’s just so sexy and classic. Already having something close to an A1 style lower helps. I have a feeling this is gonna be an expensive ride.

Do it.

I was the same way, then I built one.  Now I have it stripped down to be a holland and I'm sitting here debating selling all of the mod 0 parts for another FF ras rail.  The only thing stopping me is the fear that PRI goes tits up and the parts sky rocket in cost.

Just placed the order for a Ballistic Advantage 18" SPR bball. Monmouth Reloading is having a sale. I think 25% off BA barrels.

On another note, how hard is it too find the collar and muzzle brake. I'm guessing that and the forearm might be the hardest part to find. But I could be wrong.

Those are the easy parts, you'll see.  Brake/collar, https://adcofirearms.com and the forearm at http://www.precisionreflex.com

Poor guy.  First time I ever saw the top rail backordered lol

That's a nice looking setup! My friend is building one with a SOPMOD right now as well. I might have to try it out. I have long arms so the a2 feels pretty good, but I hear you on the portability.

Humm, you might be right. I'll have to measure it. I can always hunt down the correct one.

That's where I picked up my barrel as well. It was a good deal. For the brake: https://adcofirearms.com/products/manufacturer/allen-engineering/mountscollars/ For the rail PRI, Brownells, or check the EE on here. They come up from time to time.

So what're the hardest part to find?

For a Mod 1, the handguard.  They are still in production, but are only released in 2-3 batches per year.  If you don't snag one up then, then you have to maintain vigilance on the EE (or just post a WTB ad).

Reproduction Mod 0 parts are more-or-less available.

Well then I'm in like Flynn. I gotsta have that Mod 0 goodness.

In my experience, the hardest parts to find are -

Mod 0:
Original Mod 0 parts (most settle for retro reproductions) - front sight, hand guard, Swan sleeve

Mod 1:
Mod 1 Hand guard

Mod H:
Correct Gen 3 ACE SOCOM stock

Common:
Original KAC trigger (most settle for the Geissele)
Original optics (most settle for re-releases)
Original optic rings/mounts (most machine the new rings down)
Certain parts of the Eagle sling kit (KAC mount, sling silencer straps)
The cash to buy a registered receiver and a spouse that will let you spend it

Actual ARMS #38 sleeves. #38-PEQ-2-3 are hard enough to find, and #38 SPR-MOD or PEQ-2 versions are even harder. You can build a nice Mod 0 using PRI's copy of the #38 sleeves but if you're really trying to get the rifle to be correct expect to pay $400+, or modify an Airsoft #38 sleeve.

It all depends on how far down the rabbit hole you want to go. If you're talking about going balls out museum replica level, the tough parts are the #38 sleeve, a Colt AF forge marked upper, and some #22 Medium ARMS rings without the later "humps" that prevent the levers going past 90 degrees. The optic is also a challenge if you want an actual period correct 3-9 TS30. Otherwise, just buy a non-TS30 marked 2.5-8 with M2 turrets and Illum Mildot and try to score a Mk12 turret for it. If not, you should be able to provide general Mk262 ammo data to Leupold and have them do a custom turret engraved, since some of the TS30s or 3.5-10s still around in group armories had different turret markings. Hell, before 2004 or so they were still using 62gr M855 turrets.

You can make it as hard or easy as you want, all depends on what level of "clone" you're shooting for. Anymore, I'd build a solid shooter that you can go and flog on. Paint it, hunt with it, drag it through the mud. You can replace with more "correct" parts as you go.

Fixed that for ya.

I think I’m gonna go with the repro parts. I know it’s the easy way out but I’m not necessarily patient enough to go full bore clone.

Ops Inc 12th Model Suppressor

Lol.

Lucky for me I already have one.

That is pretty amazing cause they are hard to come by. I believe I know where a few new ones are left still if you're willing to buck up and pay the big money

Is it really that hard to find them and where do you find them?

What we're not telling you is that years ago, they were only sold to the military and then they were released for civvies and then some period of time passed and they are no longer made.

I know of a guy who has 2 left in stock. Probably the same person cjwwd2 is talking about. He told me $1,700 for one... I chose the AEM5 instead.

I was unaware they were no longer made. I though they were still in production.

Edit: Double post

Most of what you see are Allen Engineering AEM5s.

Oh ok. I’m assuming he’s referring to an actual Ops Inc produced 12th Model.

Correct. I should have been more specific. OPS Inc 12th model cans are no longer produced. IIRC, around 2013 (ish)?

What would be more correct? A black or grey A1 lower?

In no particular order:

Show off!!

Outstanding collection!! Damn do I need a set of those rings without and stop humps.

Man, that Mod 0 is sexy. I can only hope mine will look that gorgeous.

Gen 3 is correct - no one has taken the time to update the front page of the Mod H thread:

Mod H ACE SOCOM info

I omitted the Ops Inc 12th cans because aside from markings, the AEM5 is the same thing.  The important thing with this part is to specify knurling or not at the time of ordering.  According to AEM, both are correct but you cannot add knurling after manufacture due to the mandrel required for the process.

If it's truly a gen 3, then the newest replacement tube will fit in the stock with the square button, because doublestar doesn't sell gen 1 parts currently. And if memory serves me correctly, haveblue whatever had to mill a custom tube for his, because double star said replacement buffer tubes only fit gen 2 and newer. So does a new tube fit on the stock with the square button? I'm gonna put money on no, because it's a crude design that if somebody came up with that stock with screw in swivels and a clamp after other designs, then that's a complete failure of an engineering department. It makes no sense it's a gen 3.

I've been meaning to talk to you about that.  I called Ace a couple weeks ago, I think after our last convo about this, and got two COMPLETELY different answers.  The more competent sounding person said it was a gen 1, the more aloof person actually said she thought it was their gen 2 and if I'd give her my email she would check for sure.  Since then nothing.

Was there a person you remember talking to that really knew their stuff?  As soon as I get a firm answer Ill change it, but not until.  That's just responsible.

I'm not doubting anyone, facts are facts, just confirming which is what I do at my job when doing research.

I'll do some research on my end, got a couple ideas to get down to this, that's about all we can do at this point. When exactly did the first Mod H rifles with the ACE ship from PRI? was it 2008?

Well I ordered a Badger #30697...should be here Friday.  Wonder how off my elevation is going to be off initially since it's 20moa mount and .25" taller than my NF rings...  Obvious answer would be 20" lol but not sure about the height difference and how it will affect it.

I run 20moa mounts on both my bolt guns, so don't expect having much trouble sighting in at 100yd, hopefully.

my KAC unimount is said to be 19moa....I switched from the NF to the KAC mount and at 100yds it was indeed 19 clicks to get back to enter :)

I was pleased.

Yes - the person I talked to knew his stuff and said he was constantly correcting people that called in to order parts.  There was a phone conversation, but the meat of it was over e-mail.  I do not know if he still works there, but his name was Tim Mourning.  I'll quote the e-mail chain below, but I'll also note that I provided image history year-by-year in a previous post showing the round button was first, then the square button, and lastly the pill-shaped button (in terms of availability of the variants).

See the middle of this page: HERE

This isn't the first time I've done this kind of research - I'm the sole author of the Mk14 clone spreadsheet over on the M14forum (if you're bored...) and I completely understand you wanting proof... but regardless of what DoubleStar tells you over the phone, checking actual image history year-by-year online should still be the gold standard.

Two more facts to keep in mind:

1. I could order the square Gen 2/3 tube in 2017.  I could NOT order the round Gen 1 tube.
2. E-mail dates start 3/27/17, for a reference point when Tim refers to Gen 3 being used "9 years ago".

Lastly, the Gen 2/3 tube part I ordered was exactly what I needed.  Two images referred to above are shown below:

I'll throw out the only argument I've really seen to the above, as well:



The Atlas bipod, lack of sear pin, and round stock button all lead me to believe this was a design prototype and may have been pieced together from parts on hand (hence the older stock).  I'd let everyone form their own opinion about this one - even if it was a prototype at PRI, it would be a tough sell to call this one 'as-issued' without a sear hole.

That belongs to member Glass1 who at the time worked for Badger Ordnance. I believe that was his personal clone.

He used to post in the clone threads quite a bit, but people were dicks and ran him off.

What’s the rough weight difference between a Mod 0 and a Mod 1. I know it depends on accessories of course but I think I remember reading that the Mod 1 was lighter.

All up, I think my last estimate was between 0.25 and 0.75 lb.  Much of it depends on what all you consider - stripped upper or with accessories common to the Mod 0 vs. Mod 1?  If you weigh the Swan sleeve, you'll probably be within 10% of your actual weight difference with stripped uppers.

Yeah with most common accessories attached. Was curious cause I’m conflicted on what to build. Really wanna build a Mod 0 cause I think they’re sexy but I also wanna build a Mod 1 cause it’s the rifle the Navy used, and if I remember correctly, my uncle carried one while in the Navy. So that got me wondering about the weight difference. And yes I know the logical answer is to build both

My 2 cents is honor your uncle and build the mod 1. Screw the weight either way...

If you're worried about a half pound then do some pushups.

Kidding aside, the mod 1 is lighter.

Yeah I think I’ll do the Mod 1. A1 stocks are kosher for Mod 1’s, right? Already got one on my SPR inspired build that I can steal for this. And where do I find the KAC FF rail besides the EE? Ugh this won’t be easy.

Yes, A1 stock is good.

I'll shoot you an email with websites. I don't think you're supposed to post them or some crap.

It's shouldn't be too difficult for ya.

Get on the notify list at Operation Parts.  Email Dennis Todd as well.