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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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I see a mod h I'm the new .224 Valkyrie in your future.

If you haven't tried uspsa open class that's a rush, but say goodbye to money if you do.  The clone game is not the most expensive game around as it turns out.

not all mod H were noveske barrelled. some have unmarked barrels. verified.

BA barrels are not the correct profile and in 1/8 only. for a barrel thats getting a 22oz can on the end, it willl matter. ive got a WOA Barrel of the correct profile. The can make them to order last i heard. some have said they  made the ops cut 2.3 not 2.4" back, but i have a lathe and thats a 10min setup and cut back if i need to massage it.

It's listed under Leupold Mk4

Ahh, there it is. Thanks!

I really need those rings without the stop humps. lol

I tend to agree with you on the 22oz can on the end of those barrels. Seems I'm collecting barrels now. lol. I went ahead and bought a BA 16". Bought it from Granite Ridge Outfitters for $134.55 delivered. Can't go wrong with that even if I just use it for something else. But to your point, I have a WOA that's an 18" and it's a tack driver. May look at that them for the 16".

And idea what the history is behind the unmarked barrels? gov't contract co X or turned down barrel blanks?

I'm starting to think everyone is a bad influence on me because I just keep buying and buying and buying......

Lol, nature of the beast.  Honestly, if I was going to go all out with the correct profile I'd order a Bartlain or Criterion barrel from Compass Lake.

John only made a select amount of barrels for the original order.  Uppers sent out after that original very likely had barrels from PRI, they have a few with the correct profile.

The next time I do a Holland upper, I may go with the Bison Armory one and give them a try. The heavier SPR style profile as mentioned, $200 and add bead blast for $20, 1:7 twist. I've heard good things about them here and that was with the Recon profile that's closer to the BA TacGov.

Bison 16" SPR tube

And yes, you read that right. Hollandless for now but I plan to do it "right" when the time comes again, FDE handguard and FDE Duracoated upper with the right forge marks, Bison barrel bead blasted. Goal is 1:1 of the Holland carried by the gentleman from KRG Ops.

Please confirm for me " the right forge marks"?

Well for the upper I was doing, it was just a Keyhole/Cerro, no Colt "C" or other stamps. Basically the Hollands should mainly have used new contract stripped uppers, though some may have re-used the SPR uppers if they were still serviceable as evidenced by upper/lower paint matching but the handguard being FDE Duracoat.

I'm copying the top upper here:


A plain Keyhole, or maybe Square forge mark should be fine.

That’s the pic that got me into the Holland game

It's certainly one of the most convincing out there. FDE Hollands just got it going on.

OKay, good to know! I was misinformed that the upper receiver was also "C" stamped. Good thing I have the keyhole upper without any other markings. Finally something I don't have to buy.

If one was rebuilt on an SPR upper, then it possibly would have a Colt but it would be an "AF" forge mark.

There's no one pattern with them, some had FDE handguards and upper, some were FDE handguard, black upper, some were black/black, some had rattlecan on the upper but not the handguard, it's all a mix.

Lance is right.  Basically, they took the old spr (MK12 mod 0) rifles and took what they could use and trashed the rest.  In many cases new stripped uppers were used and they aren't marked with the c.  One of just several reasons the holland is one of the cheaper spr clones to build.

Check out page 1 of the holland thread also

Great to know and I had no idea about the Holland thread! After reading 4 of 43, I appreciate everyone answering my questions. Seems some of it was covered there! I'll try and get through the other 39 pages tonight.

Same here.

I wouldn't sweat the small details too much, the H in mod H stands for "put whatever the Hell you want on it" pretty much lol as there are many many mod-H variations out there, unlike most of the stricter Mod0/1 as-issued/builds.  It's the perfect rifle to enter into the cloning world, lot's of leeway.

Sorry for the noob question, could someone point me in the right direction on deciding on a rear BUIS? I’m using the peq 2 rail from PRI and the clearance is minimal as seen in the pictures below. Thanks in advance to any replies

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The ARMS 40L is designed to fit under that little "ledge" of the rail.

Thank you!!

Making moves to buy the can.  It will be my first NFA buy.  NFA has always intimidated me, dunno why.  I can only imagine the floodgates will now be opening.

Easiest money you'll ever spend. Most places make the process turnkey. Congrats.

Up until very recently most places made it seem like a dark art.  It didn't help that I know no one IRL with nfa toys.  NFA dealers around me were jerkoffs (i.e. the only one for the longest time was raided by the ATF, then had a SWAT standoff at his home).  Times have changed, and/or I stopped being a bitch

lol, sounds like you need better mates.

The ARMS 40 full size and the PRI rear sights will, as well.

Hell ya!

Brad

It's all in Michigan, mixed with road salt.  Every time the roads dry up a bit, and I think it's safe to wash my truck, it dumps again and I'm covered in salt.  I hate road salt.

Is the mk12 18" barrel and rifle gas system a reliable system if run without a suppressor? I would assume that since the dwell time is shorter, that it may be a little finicky unless either suppressed or the gas port is larger. Ive been interested in these for awhile, but not so sure I would be getting a suppressor and reliability is #1 followed by accuracy. Thanks in advance for any feedback.

Yes.

Halleluja, I'm getting the Mod 1 Handguard and at not too bad of a price
All the rest is no problem at all, luckily one of my mates has someone who does imports at a very good price on speed-dial.

This year is starting well

Nice, make sure to get pics up as it's coming along

Wilco
Handguard, DD MK12 Gas Block, KAC Rear and Front sight and the Arms #32 are coming first, all the other stuff I can order locally, gunsmith has recievers, a DPMS MK12 barrel, BCG and all the small parts, plan is going well so far :D

I did a thing.  It will be my first can.

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Grats!

There's no way a sports shooter will ever get a surpressor over here...

Niiice! These cans are so underrated, it's not even funny.

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It's a gooood thing!

Nice. I too did a thing on December 6th, went pending on the 22nd

those 2 ACS stocked Mod H represent my basis for my clone. i had it like the other one with the FDE magpul MVG on it and SOCOM stock for awhile, but the ACS is lovely. i had a larue lt104 on mine for 1 day as i was wanting to clone to top rifle more closely, but 3" groups arent my style so i had to go back to RECCE rail. There are a lot of options for mod H. its not much cheaper tho...im at $3,400 in the pelican and can that is about $250 cheaper than an AEM5 lol

also, dont forget the Diemaco for Anchor Harvey upper. also an option :)

Why did the LT104 impact your groups?

Bought mine from Presample Depot too. ATF cashed my check on 12/12/17. I hope going the trust route wasn't too much of a mistake. Hopefully they get the wait times down.

Definitely underrated.

AEM5 is my favorite centerfire rifle can I own. Todd Magee of Dead Air posted the other day in the silencer forum that it is the quietest 5.56 can he's ever tested at both muzzle and ear. Pretty solid endorsement from another manufacturer.

It helps that Eric is the man and a fellow hardcore cloner.

Edit - kind of killed the budget for buying an MRE when they become available

Funny thing is I've never had a problem running the rifle suppressed or unsuppressed with actual MK262 or my own handloads. I've read so many postings by people over the years with regards other upper combos that they needed to have an adjustable gas block, no sure the reason why, when the MK12 gets the job done as it was originally built.

The firearms blog did a little article a couple of years ago. Phil Seberger was a bit off a genuis, even his methods of measuring the suppressors sound waves was innovative, so much so that the Aberdeen Proving grounds started using his methods. Utterly fantastic suppressor, so many people I know still can't believe how quiet and effective it is.

I've been trying out adjustable carriers in my short and suppressed rigs to mitigate excess gas. Needless to say I didn't even need one for my 16" recce with the AEM5. The rifle just flat out runs great.

Have we done this one yet?

NSW OIF:

never found out why. it grouped then dropped shots 3" low, and wandering zero issues. 2 days at the range, 60rnds of handloads....veey frustrating. i wasnt a fan of the way you mount or the procedure for tightening...that i did 2x and watched a youtube video on to make sure it wasnt me. i heard AFTER that some people i asked quietly had issues with them....SO i returned it immediately. i could also flex the optic in the mount by applying pressure to the optic....didnt like that. i know that Mark goes through the threads and i didnt wanna really say too much negative on it cause he would come hard. i bought mine during that $149 sale.

loving my recce and NF combo tho :). the issues immediately stopped at the range when i went back to that setup.