Stag AR-15 flattop rail out of spec?

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platnumbob

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I recently acquired a stag AR and ordered a buris Fast Fire III with the AR-F3 riser as an optic. Well I got the AR F3 today and to my surprise when I try and mount it to the rail it has some serious forward and back play (ie. it actually slides forward and back) after being tightened down. I took my trijicon tr24 with adm mount off my Swiss arms to try on the AR and same problem....the fast fire AR F3 seems to mount fine on the Swiss.

Am I missing something? It is almost as if the AR flattop is not wide enough to be fully tightened down to.

In case it matters the PO had a big scope mounted with Leupold rings which apparently fit snug.
 
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Own two Stag uppers works just fine with Vortex, Aimpoint, Nikon, Eotech, Meopro, Burris and Brushnell mounts, so I am certain they are in spec.
 
The rail is literally just the flat top of the upper (ie integrated). Assuming the rail is out of spec does stag warranty parts after the original purchaser? I do Happen to have the original receipt - it was bought at TSE.
 
The rail on my Stag 3G upper is at the low end of the specification at 0.830" while the Noveske NSR 16.7" rail I have installed on it is at the high end of the specification at 0.835".
Both accept various scopes and accessories without issue.
You do realize that most accessories do have adjustments built in if they are of the quick release type.
If they are not quick release most mounts with 1/4" threads call for 60 in.lbs. of torque.
 
platnumbob said:
I recently acquired a stag AR and ordered a buris Fast Fire III with the AR-F3 riser as an optic. Well I got the AR F3 today and to my surprise when I try and mount it to the rail it has some serious forward and back play (ie. it actually slides forward and back) after being tightened down. I took my trijicon tr24 with adm mount off my Swiss arms to try on the AR and same problem....the fast fire AR F3 seems to mount fine on the Swiss.

Am I missing something? It is almost as if the AR flattop is not wide enough to be fully tightened down to.

In case it matters the PO had a big scope mounted with Leupold rings which apparently fit snug.
Click to expand...

Your ADM Mount is adjustable to fit various rails. My assumption would be that the mount needs simple adjustment rather than the upper being out of spec.
 
thump_rrr said:
The rail on my Stag 3G upper is at the low end of the specification at 0.830" while the Noveske NSR 16.7" rail I have installed on it is at the high end of the specification at 0.835".
Both accept various scopes and accessories without issue.
You do realize that most accessories do have adjustments built in if they are of the quick release type.
If they are not quick release most mounts with 1/4" threads call for 60 in.lbs. of torque.
Click to expand...

The .835 -.005 is not an important measurement. It is in fact almost completely irrelevant. The measurement .748 +/-.002 is the one you want to measure, but it is unfortunately unmeasureable without either fancy tools or special fixtures.
 
So, in measuring the top width of the rail (measure tape - that's all I have), the stag flat top rail I have is 25/32". In comparison the Troy alpha rail I ordered is 27/32" and my Swiss arms top rail is 26/32". I really have no way to take any other measurements, but it's interesting that the stag flat top is the most narrow (and that they are not all the same).

The Burris fast fire III AR F3 is not a QR mount so no adjustment. When I popped it on the Troy alpha rail and on my Swiss arms rail I could finger tighten the nut of the optic mount and it was dead tight with no movement. When doing the same finger tight install on my stag AR the mount was sloppy and the optic slid forward and back- this sloppiness remained the same after also using the supplied wrench to tighten down the nut (the supplied wrench for the AR F3 is really small, not allowing for much force to be applied - it actually fits in a storage compartment within the mount itself, along with other tools, for those who are not familiar with these).

Anyways after coming back home after this weekend and reading thump rrr's post about 60 lbs torque I figured I would try a bigger wrench and really tighten down that bolt - turns out with a good hard turn (and a real wrench not the little factory supplied one) the mount does tighten down to the stag flat top. There is a crush washer in the mount that must have needed a good push. So - thanks all, looks like I am good to go. I guess I learned that not all mil spec rails are the same; which was my starting assumption leading me to foolishly assume that the mount would hand tighten install the same on each of the 3 rails I was working with.
 
I'd argue that your assumption that your sight mount is in spec is likely the bigger issue.
 
Leg said:
I'd argue that your assumption that your sight mount is in spec is likely the bigger issue.
Click to expand...

That is possible, I really have no way to confirm that - although it easily and firmly mounted to the other two rails mentioned with simple hand tension (the troy and the swiss rail). The troy rail is visually/ noticeably wider than the Stag flat-top when placed side by side.

Either way, it seems to be on solid now so I am happy.
 
Yeah, contrary to what people believe military specification is not a precise set numbers, but a set of acceptable loose tolerances. Because in the military mixing well worn parts and brand new parts is a standard practice.
 
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