Does anyone know what gas systems are used on SR-15 mod 2’s and if they are proprietary, how long are they?
The whole system is proprietary. The gas block is locked in with a castle nut and the gas tube has a pneumatic style connector sort of thing.
I think the gas port is like 11.2" or 11.5" from the standing face of the receiver. Very similar to the intermediate length offered by other manufacturers.
Knights calls it “a proprietary mid-length gas system” but as others have stated, it’s more like a intermediate. Below is an excerpt from Knights Armament’s description. The link is at the bottom.
“The Knight’s SR-15 Mod 2 line represents the pinnacle of firearms based upon the Eugene Stoner designed operating system. The Mod 2 update introduces several notable features to the SR-15 IWS line. The chrome lined 5.56mm NATO barrel features a proprietary mid-length gas system that increases reliability and durability while also reducing felt recoil. The Mod 2 gas system minimizes the chances of gas leakage and ensures more consistent operation in harsh conditions. The new gas block is secured with a locking ring instead of taper pins, which increases barrel rigidity and eliminates the need to custom fit the gas block to the barrel.”
https://www.knightarmco.com/4685/shop/commercial-firearms/sr-15-carbine-mod-2-2
Is there a particular reason that you ask?
I might be able to help cut to the chase.
Want a pic rail on instead of Mlok or KM. I know there are clearance issue with the new gas blocks. I’d like to put a RIS II on it, but if the gas block sticks out or it just doesn’t fit, I’ll leave it as is probably.
Edit: I am wondering on a 14.5in. Will the RIS II cover the gas block?
You’d need to know the size of the top of the gas block where it bolts up and how much clearance the top rib/channel of the rail has to be to allow for the bolt-up gas system. If the rail you intend to use has the same or more generous internal dimensions than the URX4…you’d be good to go. I too have contemplated doing something similar in putting a 3.1 on an ACC and the same on the SR15 with a Mk1 Geissele rail.
Isn’t the gas tube connected with a Flare connection?
I didn’t consider that, but that would be very interesting. Wasn’t there a 13" Mk1? That on a 14.5 would be probably better than what I am thinking 
This is the Mod 2 system:
AN type fitting, yes
It won’t fit due to the height of the gas block. That said, you could simply attach rail sections at the 3, 6, and 9 and get the same effect, with no need to wrench on the gun.
Lol @ leaving rail sections without using them. Kinda defeats the purpose of Mlok.
Why the hell would you want to replace the URX 4 rail? If you want a pic rail go seek out a Legacy rifle.
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It’s a lot less stupider than wasting the time, money, effort and brain cells to replace a perfectly good rail system off a perfectly good rifle and replacing it with another rail system that literally does the exact same thing.
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The top rail/upper doesn’t sit any higher on a KAC than any other AR (unlike say an HK 416)…just how much more clearance does the URX4 have given that some others on the market are rather generous. I always wished KAC were more forthcoming with their dimensions and specs…
The legacy stuff is stupidly priced on the open market. In my case, I could have bought an ACC, a URX 3.1, and pay Marvin handsomely to change it out for what an ECC would have cost. Or how bout a nice used Mod 1 for $2.7k? I also enjoy seeing what some of the Grade B EMC’s are being priced at when they turn up from time to time…
I really like what KAC has going on under the hood so to speak in terms of barrels/BCG’s and what not, but I have issues with other aspects…one being the URX4. Just because YOU don’t understand something doesn’t mean the concept is any more or less valid. But you are right though…ultimately trying to cram the square peg in a round hole just wasn’t worth it.
Says the genius that wants to replace an MLOK rail with pic…
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I don’t like Mlok or keymod
I don’t like you. How dare you bastardize Eugene Stoners masterpiece.
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I forgot about the time he made Mlok or Keymod