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
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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.
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.
http://www.freeimagehosting.net/u8l15
note: not sure why my pic does not work it can be found here: http://www.freeimagehosting.net/u8l15
This may be old news; but I just ran across this on ADCOs website. They do it for 55.