I got a 13.5" NSR over the weekend and want to drill my Vltor MUR for the anti-rotation pin the NSR’s have. Is there any kind of jig or drawings that show where this hole needs to be? I have the tools and know how needed, just want it to be exact.
Or would it be best to find an actual Noveske MUR pre-drilled?
Where is this pin?
I put an NSR and Noveske MUR together a few weeks back and don’t remember anything about an anti-rote pin.
The pin is hidden, unlike most other manufacturers, and it should have come with the NSR (mine did). Installing the pin is optional, but when used it helps ‘lock’ the handguard/barrel nut to the upper receiver to prevent the nut from back out.
Great topic as I was looking to drill my standard upper for the NSR anti rotation pin.
Judging from the photos, there may not be enough room to drill the upper for the pin
Wow… I don’t remember seeing the pin. I’ll have to look around.
I’d rather leave it off than drill into my upper.
??? Judging by the pictures, there’s plenty of room to do it. The anti-rotation pin hole is shown in the picture of the MUR receiver.
From bore centerline, the height to the gas tube hole and to the top of the receiver’s rail is the same if it’s a MUR or M4 receiver. So by that logic, the hole for an anti-rotation pin would be in the exact same location on a M4 receiver.
That being said, I have personally drilled the hole on a standard M4 receiver to accept the anti-rotation pin for a NSR. It worked fine and was very simple after the setup in the mill was complete. I don’t have the measurements we took anymore but I can give you step by step on how I did everything. If the desire is there, I will post it in this thread, maybe with pictures if you ask extra nice.
If I had regular access to the machine shop, or if someone wants to buy me a bench top mill, I would gladly do it for anyone who wanted it but I can’t foresee either happening in the near future.
I found the pictures on google, the one on the left is not a true representation of the standard Vltor MUR. The one on the right is a real Noveske marked MUR. A standard MUR is mil-spec forward of the dust cover.
Can you post the steps please? I have access to a Bridgeport, I just need the measurements. If it’s not just right, the NSR might be canted or may the anti-rotation pin might not fit at all?
Theoretically, the hole to be drilled in the upper receiver will use the same measurement as the anti-rotation pin hole already in the NSR… it may work on paper, but that doesn’t always equate to real life…
The NSR 9 that I installed a couple of days ago had the anti-rotation pin in the little bag with the rail screws. The upper on the rifle I installed it on is a Noveske from a couple of years ago and of course wasn’t drilled. It strikes me that drilling the receiver would be a pretty critical step and accuracy of the drilling very important if you want the rail on straight. As it is, the only thing that would allow rotation of the upper is if the barrel nut came loose. I torqued it down with 80 ft-lbs, so I doubt that that’s likely. The rail that I replaced was a DD Lite 9.0, which also relies only on the barrel nut to keep the rail from rotating. I never had that happen, and reviews of the DD Lite over its market lifetime certainly suggest that it’s not likely. I decided not to worry about it.
Got it. I was judging by the photos. The receiver on the left has a larger gas tube hole (in fact, I was wondering if that hole wasn’t enlarged for a piston setup) and doesn’t leave much room for the pin between the hole & top
good point, it probably is for a piston setup.
I would cover the end of the receiver with a piece of masking tape and make a centerline.
I would then install the handguard with the pin installed.
I would have the end of the pin covered in prussian blue which will clearly mark the arc of the pin.
I would then use a center punch to mark the center of the hole.
If you have access to a milling machine I would not use the centerpunch but I would use a vernier caliper to find the height of the centering pin.
Best of luck.
I would like to reiterate that you will have to take your own measurements as our measurements were specific to that receiver and NSR. Not only would they most certainly be incorrect for the large spectrum of in and out of spec receivers, I do not have the measurements we took. The paper that they were written on is in the loving care of Waste Management. So you will have to decide whether you are comfortable taking these measurements and doing the work or if you want to pay someone else to do it. I refuse to take any responsibility for your actions, unless you do a really good job. Then I take full responsibility…
I would also like to note that I went way overboard with my method of measurement. There are quicker and easier approaches to it but that’s not how I roll. Either way, it’s going to take me longer to type this description than it did for most of the actual work. I promise this will be long winded. Also, I have attempted to write in straight forward and over simplified terms so hopefully even someone with minimal machining experience could follow along. So forgive me if some points seem unnecessary.
1: The easiest way I could come up with to assure my measurements transferred from the NSR to the receiver was to assemble the two and then measure for a difference in height to the tops of their respective rails. This was measured on a Starrett Optical Comparator. His Brand X receiver was slightly higher so we recorded the difference and saved the number for later. We’ll call it Measurement A. If you don’t have an optical comparator, you could use a vernier/calipers as a height gauge to get a good measurement.
2: The pin supplied with the rail didn’t fit how I wanted so I hopped over to a lathe and spun up a new temporary pin that was a “snug slip fit.” It could be inserted/removed by hand but there was VERY minimal play. I went back to the optical comparator and took Measurement B from the top of the pin to the top of the receiver. I already knew the radius of the pin, Measurement C, so:
B + C = Measurement D, the distance from the centerline of anti-rotation pin hole to the top of the receiver. Recorded that number and moved on.
3: Next the overall width of the receiver was measured with a Starrett dial caliper and then the measurement was divided in half, giving Measurement E. This measurement is the “vertical centerline” which I used to locate the hole in the receiver.
4: A + D = Measurement F which is the horizontal centerline for the anti-rotation hole.
5: So now I have measurements E and F which will locate the hole on the upper receiver to match the NSR’s hole.
6: Now I fixtured the receiver in the mill. You’re on your own to figure it out, I’m not giving away all my secrets. Please make sure to check that it is secure and true with the spindle.
7: Found my edges and zero’d out the DRO. I then swapped to an end mill. If I need to describe that I can, I’m getting tired of typing.
8: I moved down F from the top of the receiver (Y-axis) and came in E from the side (X-axis). Your axes will obviously be dependent on how you orient the receiver in the mill when fixturing.
9: Only thing left is to plunge cut the hole. Since I was going to make the anti-rotation pin myself to assure a tight fit, I got to pick the depth of the hole. I think I went a quarter inch (.250") into the receiver but I’d have to double check.
10: Chamfered the hole a little to make it look pretty.
11: Machined a pin to slight interference fit and tapped it in with a piece of wood dowel. Notice there’s no mention of hammers there?
12: Assembled the barrel, barrel nut, gas block and then installed the NSR.
I hope that helps someone. It gave me a headache. Please ask questions so I can clarify anything if needed.
See I knew someone would have a simpler way of doing it. 
Apparently, it took me hours to write my response because yours was not there when I started and there’s quite a gap in time between our posts. I need a beer.
Agreed. I replaced a DD Omega X last year and I’ve never heard of any issues with that setup and the NSR is much more robust.
If you are that worried about it and your optic allows for eye relief move your optic mount slightly forward so it just sits on the very back of the NSR. Redneck anti-rotation ‘tab’
-Jax
Thank you everyone! Once I do this, I will document in this thread as the measurements have to be just right for everything to line up perfectly.
The Mur I have does not look like either of the other photos. It looks just like the Noveske one except it lacks the hole. It looks like there is room to do the roll pin mod.
I wonder if Noveske could provide a template for drilling.
note: not sure why my pic does not work it can be found here: http://www.freeimagehosting.net/u8l15
I would have just stood the receiver up and verified it was square, then indicated off the bore with my coax indicator and then moved straight up the proper amount.
No need to be working from any outside edges…
This may be old news; but I just ran across this on ADCOs website. They do it for 55.