AR-15 reliability question again..... mark 12

[AngelZ3R0]

Reliability is my question. I want to build a SPR mark 12ish type rifle. I want the 18 inch barrel with rifle length gas system, Im going fixed rifle stock with rifle buffer system. I tend to see alot of people with carbine buffer systems, I always was told rifle buffer was better the carbine buffer. Is this true? also is there gassing issues due to having to over port it due to less dwell time. Is it also true that 20 inch fixed stock tends to be the most reliable in theory. So would 18 inch be less reliable in theory.

PS Im having to much have fun with AR 15 builder.

[desert dog]

Reliability is my question. I want to build a SPR mark 12ish type rifle. I want the 18 inch barrel with rifle length gas system, Im going fixed rifle stock with rile buffer system. I tend to see alot of people with carbine buffer systems.

This is because the ACTUAL MK12s used a carbine-length gas system. Correction, they used a rifle length system but many civy builders prefer to do it with the middy system. Most of the RECCE projects I see are done with a carbine system.

Manufactures jumped on the marketing hype once they found out the SEALs were using them in a limited capacity. And started marketing precision rifles as "MK12s", "SPRs", and "RECCE". Now you see anything with a heavy barrel and free-floated rail being categorized as such. Since most precision AR shooters prefer the mid-length gas system, Wylde chambers, and other features - the rifles they sell naturally progressed into that. Before this hype, they were just called "precision ARs". HCS sells the most authentic examples.

The Irony is that the MK12 was not well received by SOF, and is all but phased out now in favor of 7.62 guns that are lighter and more compact like the SCAR-H and KAC.

" I’m not a big fan of anything 5.56 and I personally avoided carrying the Mk-12 in favor of the 300 win mag or 7.62 semi.

The 5.56 round itself is just substandard all around in my opinion. The only thing I would consider it good for is sub 300 yards urban operations, but you better make head shots. And if you’ve ever shot someone in the head it’s a damn hard shot to make in a critical situation. Peoples heads bob back and forth and move around constantly. Better to go center mass to the chest with 175 grains of 7.62 boat tail hollow point. It’s the kind of chest pain that ends quickly and never comes back….
The Mk-12 would make a good paper weight, that’s about it…."
- Brandon Webb, SEAL team 3

SEALs, say they've never heard of Recce rifles, and that the Recce rifle is just an internet fanboy invention. When you describe what one is, however, they quite frequently will say, "Oh yeah, I've seen those." I corresponded with Kyle DeFoor, a well-known firearms trainer, TV personality and former SEAL sniper, on the subject. He indicated they usually just called them "sniper M4s," as they had no official designation. Defoor stated that the 18-inch barreled Mk 12 SPR was just too long and heavy, especially once you attach a suppressor.
- SGN interview with former SEAL sniper Kyle Defoor

[MrPlink]

According to resident SPR experts here and elsewhere the original model (not yet designated as Mk12) was more or less what is called a RECCE. Crane caught wind of the idea and turned out their version which is the Mk12 we all know. There are several versions under various names depending on who is using it.

FMJBT might be a good person to chime in here.

And while the teams or devgru etc may not be using them they certainly have shown up with others and are still in use.

[MrPlink]

And to the OP. Pick whichever you want and fine tune from there. If you are really worried look at the vltor A5 system.

[G21Shooter]

I would get a mid length gas system with a 18 inch barrel.

[AngelZ3R0]

And to the OP. Pick whichever you want and fine tune from there. If you are really worried look at the vltor A5 system.

Im not worried just wondering why there are different systems. pros/cons

I would get a mid length gas system with a 18 inch barrel.

why?

[G21Shooter]

why?

The rifle length has system is designed for 20 inch barrels.

For a 18 inch barrel the optimum gas system length is actually between mid length and rifle length, called intermediate.

Noveske offers this on their barrels. These guys know their **** and they has this gas system on a 18 inch barrel for a reason.

http://shopnoveske.com/collections/barrels/products/diplomat-5-56mm-barrel

[AngelZ3R0]

Nice that is also another issue im having finding a 18 inch barrel. Im a small push away from just getting a 20 because I cant find any 18 inchers especially in rifle length gas system.

[Pryde]

This is because the ACTUAL MK12s used a carbine-length gas system.

Wrong, factory Mk12s had rifle length gas systems not carbine.

If you are looking for a REAL Mk12 18 inch barrel, call Compass Lake at (850) 579-1208 and ask them to make you one with a Douglas Blank, they have all of the prints and specifications to make you a perfect copy of the real thing. It cost me $350 including shipping to get one and it was only a 10 day wait.

[Wnick308]

High Caliber Sales deals with MK 12s, they also have barrels. MK 12 Mod 0/1 uses rifle length gas systems on old M16-A1 lowers that CRANE had in stock and is made to be used with m262 Mod 1 ammo(black hills 77 gr smk).


Sent 2700 feet per second.

[Wnick308]

White Oak Armament also makes a MK 12 spr barrel too.


Sent 2700 feet per second.

[desert dog]

Wrong, factory Mk12s had rifle length gas systems not carbine.

My bad. I was confusing it with the RECCE rifles that the SEALS were using, that current manufacturers like BCM and others offer in a middy. Yep both M12 mods had rifle-length gas systems.

[desert dog]

I wonder if there are still any of those actual surplus MK12 mod 0 uppers that PRI was selling to the public years ago.

[FeuerFrei]

Reliability is my question. I want to build a SPR mark 12ish type rifle. I want the 18 inch barrel with rifle length gas system, Im going fixed rifle stock with rifle buffer system. I tend to see alot of people with carbine buffer systems, I always was told rifle buffer was better the carbine buffer. Is this true? also is there gassing issues due to having to over port it due to less dwell time. Is it also true that 20 inch fixed stock tends to be the most reliable in theory. So would 18 inch be less reliable in theory.

PS Im having to much have fun with AR 15 builder.

A2 fixed stock is my personal favorite.
It will work on 20"-16"/14.5" etc.. I've shot an AR in Nevada that used a 10.5".
Reliability comes from a balanced gas system and correct spring/buffers all combined to work with the widest range of ammo. My opinion.
I hate picky weapons and I work to create the least picky.
Just use the best damn parts you can afford and plan your build before you dive in.
If you're gonna build a faux Mk12 then look up the specs and copy it. Easy enough these days.

[MrPlink]

For reference my 10.5 pistol uses a modified rifle tube and buffer and it runs like a top even with cheap steel case ammo.