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Gunsmithing How to mount scope rail in a mill

C

CSiebert

Sergeant
Full Member
Minuteman
Feb 14, 2010
161
0
48
Southeast missouri
#1
Hey guys I just had a 20 moa rail made by Bat Machine for my rifle, but when I gave them my specs I guess I measured wrong and it turned out to be too tall. I need to mill about .250 off of the bottom of the rail. My buddy has a mill but I cant think of a good way to mount it in a vice.

Ideas anyone ???
 
#2
Re: How to mount scope rail in a mill

what action is this going on? if this is going on a remington, your friend is going to need either a cnc machine or two big ass ball mills.

as far as holding it during machining, if i only had one to do, i'd probably machine a a quick set of 20 moa parallels and stick it in the vise.
 
#8
Re: How to mount scope rail in a mill

I have a AR upper holder out in the garage made by PRI I think. Its made of Aluminum and supports the upper but clamping the rails. It might work for what you are trying to do but not real sure.

p_714000006_1.jpg
 
#11
Re: How to mount scope rail in a mill

if i were planning on doing a production of them, i'd cut a beveled slot in some soft jaws at an angle that matches the desired moa cant of the base.

to do one quickly, i'd do it the way i mentioned earlier. without knowing anything about that mount a few posts back, i'd be leery of how tight it grips it and how parallel all the surfaces are.
 
#14
Re: How to mount scope rail in a mill

<span style="font-weight: bold">Warning Warning</span>

Taking .250" off the bottom will probably get into the counterbore for the screw heads. Then you have a piece of scrap aluminum and have to relocate the screw holes if that's possible.

To get the 20 MOA angle lay the base on a 6" parallel and shim one end .033" then clamp lightly. BTW the shimed end will be the front.
 
#15
Re: How to mount scope rail in a mill

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Dave Tooley</div><div class="ubbcode-body">

To get the 20 MOA angle lay the base on a 6" parallel and shim one end .033" then clamp lightly. BTW the shimed end will be the front. </div></div>

This measurement may not be correct depending on the length of the base.
 
#16
Re: How to mount scope rail in a mill

you don't have to take all .250" off with one pass , if its a decient machine vise with smooth jaw it will not take alot of pressure to hold it as long as you take care not to go slamming the tool into it to fast with to deep of a cut.

Also like mentioned before unless your base is very high i thing you may get into the counter bore of the scre holes leaving you with no shoulder for the screw head to seat on
 
#17
Re: How to mount scope rail in a mill

The counter bore is the depth of the screw head so I shouldn't have to worry about that. the rail already has 20 moa angle in it. I am gonna clamp it upside down and mill it down to lower scope height ect. I am worried about deforming the machined bevels and edges by putting it in a vise. We are gonna give it a whirl tonight and see what happens.
 
#18
Re: How to mount scope rail in a mill

Length of the base has nothing to do with it. Those measurements using a 6" parallel are correct. .001" taper per inch gives you 3.6" at 100 yds. 20 divided by 3.6 = 5.555 or .00555" taper per inch, mulitply that by 6, the length of the parallel, and you get 33.333 or .033" shim over a 6" distance. Works everytime.
 
#20
Re: How to mount scope rail in a mill

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Dave Tooley</div><div class="ubbcode-body">Length of the base has nothing to do with it. Those measurements using a 6" parallel are correct. .001" taper per inch gives you 3.6" at 100 yds. 20 divided by 3.6 = 5.555 or .00555" taper per inch, mulitply that by 6, the length of the parallel, and you get 33.333 or .033" shim over a 6" distance. Works everytime.</div></div>

I see where you're coming from now.
 
#21
Re: How to mount scope rail in a mill

I used to scope rings, a scope lapping tool and v blocks when I had to hold mine. I attached the scopes rings to the rail and lapping tool and then held it upside down between the v blocks. This gave me access to the bottom of the rail. It took more to get it straight, but I didn't have to make any custom tooling.

The rail I was milling was aluminum, this may not be strong enough for steel.

Brad
 
#22
Re: How to mount scope rail in a mill

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Dave Tooley</div><div class="ubbcode-body"><span style="font-weight: bold">Warning Warning</span>

Taking .250" off the bottom will probably get into the counterbore for the screw heads. Then you have a piece of scrap aluminum and have to relocate the screw holes if that's possible.

</div></div>

+1 Better check this before you start, seems like it was missed the first time.
 
#23
Re: How to mount scope rail in a mill

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: JBM</div><div class="ubbcode-body">I used to scope rings, a scope lapping tool and v blocks when I had to hold mine. I attached the scopes rings to the rail and lapping tool and then held it upside down between the v blocks. This gave me access to the bottom of the rail. It took more to get it straight, but I didn't have to make any custom tooling.

The rail I was milling was aluminum, this may not be strong enough for steel.

Brad </div></div>

I have milled steel talleys in this same fashion, worked great. By mismatchin the bases with another set that had a taller rear base I was able to get enough angle in the bases so that I am only 9 MOA from having the scope bottomed out. I had to touch up the screw holes but it works great and saved me big bucks on a nesika rail.
 
#24
Re: How to mount scope rail in a mill

Well fellas I milled it down last night, It took a lot a time to get it in the vise and clamped down tight (the vise would move as I tighted it, so it took repeated attempts to get it right. When I finally got it clamped in true I was a little bit high on the thin end of the rail so I ended up with more than 20 moa probably about 32 I figure. Mounted it back on the rifle and was able to get a 150 yard zero so I am happy.

Thanks for the input.
 
#25
Re: How to mount scope rail in a mill

20 moa = .333333 degree

tangent [.333333 degree] = .0058178

Over a 6" parallel bar that would be a .035" feeler gauge under one end.

Over a 5" sine bar, that would be .029" feeler gauge or pin gauge under one end.



 
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