View Full Version : Finally using a KAC URX II but . . .
red_star_republic
09-13-12, 00:39
Finally using a URX II for my upper but I'd like it to fight TIGHT on my upper.
I've noticed some people machine some of the rail off during install. I was wondering if anyone can point me in the right direction. I'm not worried about the phosphte finish because it will get rattle canned.
Sorry if this is in the wrong forum.
List of parts:
Spikes Tactical Lower
ALG Trigger Group
CTR Stock
MIAD
Enhanced Trigger Guard
Rainer Forged Flat Top Upper - I might go with a Larue Stealth
WOA 14.5 Match Barrel - Carbine Length Gas
Rainer Arms BCG - I might switch out with a Young BCG
Noveske CH
KAC URX II Mid
Optic? Eotech 512/552 or ???
Its not phosphate its anodized, but you can remove material from the rear of the rail to fit it to the upper. How much of a gap and/or how far off are you now?
Marvin Pitts would be my go-to for KAC related gunsmith work if you didn't want to do it.
Robb Jensen
09-13-12, 13:47
If an armorer/gunsmith is machining the KAC URX rail to make it fit they're doing it wrong and not using the proper tools for installation.
red_star_republic
09-13-12, 15:48
If an armorer/gunsmith is machining the KAC URX rail to make it fit they're doing it wrong and not using the proper tools for installation.
OK? MSTN has a piture up on the web where they "machined" a portion of the back part URX to close the gap between the rail and receiver amking a tight fit. I'm sure you've seen it - a lot of people have.
Found a picture of AR15.com - The receiver they used is a LaRue Stealth
http://photos.imageevent.com/smglee/mstn/huge/IMG_0102.jpg
I also recommend Marvin. He can time the rail to your upper receiver so that you do not have the typical ~1mm gap between the receiver and rail. The finished product would look exactly like the MSTN photo (if I remember correctly, Wes @ MSTN used to send Marvin work back in the days - don't know if he still does.)
Gun gallery in Jacksonville also does nice work with the KAC rails quick turn around time as well.
Yep, I have this done to all my builds.. I can't stand the gap. Its very easily done on a mill.
red_star_republic
09-14-12, 03:01
Yep, I have this done to all my builds.. I can't stand the gap. Its very easily done on a mill.
I don't have a mill and don't want to screw this one up :cool:
Robb Jensen
09-15-12, 10:19
My point as I said before is that "it's not required" for proper installation. If you wants cosmetics sure it looks nice a little closer but that's the fit & finish mentality. Some people worry about that stuff and things like "the finish of my lower doesn't match my upper" etc vs. does the gun actually work. MSTN does great work and has a solid reputation. Interesting though I don't know anyone who's complained about that gap with LaRue, Daniel Defense, Troy, Centurion, PRI, Lancer, JP etc rails...Probably because it doesn't matter and they don't lose sleep over it.
OK? MSTN has a piture up on the web where they "machined" a portion of the back part URX to close the gap between the rail and receiver amking a tight fit. I'm sure you've seen it - a lot of people have.
Found a picture of AR15.com - The receiver they used is a LaRue Stealth
Every DD rail I've installed has mated up to the upper in the exact same way. Manufacturing variances in the KAC design, be it in the rail or upper, lead some to be perfectly mated to, some have a gap.
For my money, I want it to work and be aesthetically pleasing. At the prices involved, there is no reason both can't be done, and no reason why a consumer should dismiss one in favor of the other.
red_star_republic
09-15-12, 16:34
My point as I said before is that "it's not required" for proper installation. If you wants cosmetics sure it looks nice a little closer but that's the fit & finish mentality. Some people worry about that stuff and things like "the finish of my lower doesn't match my upper" etc vs. does the gun actually work. MSTN does great work and has a solid reputation. Interesting though I don't know anyone who's complained about that gap with LaRue, Daniel Defense, Troy, Centurion, PRI, Lancer, JP etc rails...Probably because it doesn't matter and they don't lose sleep over it.
Cool - used a lot of the before mentioned rails (with exception to the PRI, Centurion, and Lancer - which is not an option). I found the LaRue Rail is a lot like the Daniel Defense M4 Rail, after that I went to the LITE series, and know I'm at the URX II. I know I'm not a profesional paper shooter so I guess it comes down to is personal preference, I prefer not to have a gap, that's why I started the thread. Plus if MSTN is doing it - it must not be that bad since everyone loves them:p I knew you weren't going to blast them directly for doing it. This is starting to sound a lot like an AR15.com thread? Or is it your not a KAC fan? Oh I see . . .
BTW: No go for Gun Gallery
red_star_republic
09-15-12, 16:36
Every DD rail I've installed has mated up to the upper in the exact same way. Manufacturing variances in the KAC design, be it in the rail or upper, lead some to be perfectly mated to, some have a gap.
For my money, I want it to work and be aesthetically pleasing. At the prices involved, there is no reason both can't be done, and no reason why a consumer should dismiss one in favor of the other.
Agreed
CharlieMike
09-16-12, 06:33
Every DD rail I've installed has mated up to the upper in the exact same way. Manufacturing variances in the KAC design, be it in the rail or upper, lead some to be perfectly mated to, some have a gap.
To be clear -- I think it is less manufacturing variances in the KAC design and more manufacturing variances in uppers.
Please correct me if I'm wrong but I believe KAC upper and rail threads are timed to mate with each other without leaving a gap.
Since KAC guns come without the gap, I can understand people's urge to achieve the same level of 'fit and finish'. Still, I think it is important to resist it and I don't see any benefit of milling the rail other than aesthetics.
At most, the gap can be a bit less than 1 thread pitch wide so well under 1/18" of an inch.
CharlieMike
09-16-12, 06:33
BTW: No go for Gun Gallery
Why is that?
Robb Jensen
09-17-12, 14:04
Cool - used a lot of the before mentioned rails (with exception to the PRI, Centurion, and Lancer - which is not an option). I found the LaRue Rail is a lot like the Daniel Defense M4 Rail, after that I went to the LITE series, and know I'm at the URX II. I know I'm not a profesional paper shooter so I guess it comes down to is personal preference, I prefer not to have a gap, that's why I started the thread. Plus if MSTN is doing it - it must not be that bad since everyone loves them:p I knew you weren't going to blast them directly for doing it. This is starting to sound a lot like an AR15.com thread? Or is it your not a KAC fan? Oh I see . . .
BTW: No go for Gun Gallery
No sorry don't do the BARF.com and I'm a big fan of KAC rails and currently have 3 uppers of my own with them.
To be clear -- I think it is less manufacturing variances in the KAC design and more manufacturing variances in uppers.
Please correct me if I'm wrong but I believe KAC upper and rail threads are timed to mate with each other without leaving a gap.
Since KAC guns come without the gap, I can understand people's urge to achieve the same level of 'fit and finish'. Still, I think it is important to resist it and I don't see any benefit of milling the rail other than aesthetics.
At most, the gap can be a bit less than 1 thread pitch wide so well under 1/18" of an inch.
My factory SR15 was slightly off. There wasn't a gap, but the rail needed to be turned a hair more to be in perfect alignment with the upper, and that wasn't going to happen w/o removing material from the rear of the rail, or having a much larger than desired gap.
I don't mind a very slight gap, similar to the DD rails when installed, I just don't want a big void there. I actually prefer the rail not to completley mate with the upper, but to have a slight, very fine gap.
The space between the upper and rail isn't what concerns me, its how flat the alignment is between the two. On one half mounts the rear sight, on the other the front sight. They need to be flat in relation to each other.
Some rail are machined slightly larger, smaller, higher or lower when compared to the top rail of the upper. If there is a gap, size variance etc, it needs to be equal on both sides of the receiver, ie no cant.
I've seen guns other people have put together and the front sight is very obviously not in vertical alignment with the rear.
How well the rail is aligned with the upper is a big tell on the quality of the assembly. If your rifle builder says it doesn't matter then move on. There are plently of places that will demand that it'd be perfect who are just as happy to take your money.
jonconsiglio
09-18-12, 08:29
I had two SR15's and honestly I don't think I ever noticed if there was a gap or not. Going back and looking at the pics, I don't see one. My current RIS II's both have a small gap (I only have one RIS II since the other upper was recently stolen but will buy another relatively soon). For me it doesn't matter as I don't bridge the gap with optics and I guess I never really thought about it.
If you want the gap closed and MSTN does the work, then go for it. Just be aware that it will do nothing in terms of function, only aesthetics, which is a valid reason for some, so I won't dismiss it even though it's not for me.
I really liked my URX II's but after two broken front sigthts and a barrel nut or rail that slightly busted loose after a fall, I'd opt for the URX 3.1 next time. I'd have to buy a wrench as well and have heard the price came down. I really like the weight and feel of these rails.
I suggest you take a step back and check yourself. You are dangerously close to being disrespectful towards mods and staff.
Cool - used a lot of the before mentioned rails (with exception to the PRI, Centurion, and Lancer - which is not an option). I found the LaRue Rail is a lot like the Daniel Defense M4 Rail, after that I went to the LITE series, and know I'm at the URX II. I know I'm not a profesional paper shooter so I guess it comes down to is personal preference, I prefer not to have a gap, that's why I started the thread. Plus if MSTN is doing it - it must not be that bad since everyone loves them:p I knew you weren't going to blast them directly for doing it. This is starting to sound a lot like an AR15.com thread? Or is it your not a KAC fan? Oh I see . . .
BTW: No go for Gun Gallery
GUNSLINGER733
09-18-12, 12:00
I feel a CLOSED thread coming on...
If you have to have it timed to your upper go for it. Either way it's still going to function the same way it did before. All my DD rails have time perfectly with my BCM uppers. I have a 11.5" BFH upper on the way with a URX II. It'll be my 1st KAC experience, pretty pumped:D
Timing the URX is a case of "it can be done" and "it looks cool" that has somehow turned into a perceived fix for a problem that doesn't exist.
IIRC, MSTN had Marvin doing the work for them along with dimpled barrels, etc. Timing the rail for a precise fit to the upper is unnecessary, but can be done if you're willing to part with the cash.
Sent from my DROID RAZR using Tapatalk 2
GUNSLINGER733
09-18-12, 17:23
Or if you have mill, lathe and 5 axis Cnc machine at your own shop;).
FWIW my factory KAC SBR upper with the URX II and KAC built-in-rear-sight upper has a gap. You cannot "time" them to make the gap magically disappear; it is done by milling off the rear of the rail to allow it to "spin" on the upper further... This is done progressively on a mill until the rail lines up tight with the upper in the proper orientation. That said I could care less about the gap as it is now but if I was getting one put together and had the option to "time" the rail and upper I would check it off. Hell, after seeing the pics of Titleist's grey OBR (the one he just sold to a lucky member) I'm considering milling mine before sending off the rail, upper, lower, and a few small parts to get it Cerakoted grey...
red_star_republic
09-19-12, 00:42
No sorry don't do the BARF.com and I'm a big fan of KAC rails and currently have 3 uppers of my own with them.
LOL BARF.com
Sorry if I came off the worng way I guess I've be warned - even though I was joking around about AR15.com (which I've seen numerous others do) and not liking KAC
I noticed you had the Surefire 556K mizzle break on your rifle and was wondering if you've had the opportunity to shoot the new SFMB 556? I guess they refined it a little and changed the method of mounting?
Love and Respect
Robb Jensen
09-19-12, 06:40
LOL BARF.com
Sorry if I came off the worng way I guess I've be warned - even though I was joking around about AR15.com (which I've seen numerous others do) and not liking KAC
I noticed you had the Surefire 556K mizzle break on your rifle and was wondering if you've had the opportunity to shoot the new SFMB 556? I guess they refined it a little and changed the method of mounting?
Love and Respect
I have not. It seems like Surefire is always tweaking their muzzle brakes. Everytime we get MB212s they look a little different.
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