I'm trying to build a small rig to use for scope testing.  I thought about buying a rail section and fastening it to a flat block of plastic or wood.  I also though about buying an AR15 upper receiver block that leaves the rail exposed (DPMS etc) and mounting it in a vice.  

What method(s) do you use?  Does the DPMS mate up solidly with upper receiver, or is there some give and play, ie, the upper wobbles around on the block a bit?

Thanks.

Whatever you'd use would have to be very rigid, as any deflection in the device would show up through the scope.  An upper in a vice seems to have potential.  

There is a guy on Snipers Hide that has been doing tracking tests with a pic rail mounted to a 12" section of I-beam.  

I-beam?  Damn, that should be solid, I didn't think of that.  I looked at vises with ball mounts and decided they'd probably be too prone to movement.  

I ordered some heavy springs to put on the four corners of a sheet of hardboard with bolts through them, then a second board on top with a rail mounted to it, and thumb nuts to let me crank down each corner against spring pressure until the contraption is level.  Figured C-clamping it to a bench or table ought to do the trick.  I have some 25lb plate weights I could drag around if the clamps didn't work.

But now I want a piece of I-beam.

Still, is it possible to do legit (or at least "this scope is totally hosed" vs "this might work as advertised") testing at very close ranges?

I mounted mine to a stripped upper clamped in my bench vise, it was very solid.

If i were going to do many scopes, I would mount a rail to a block of aluminum that I would  clamp in the vice.


The distance doesn't matter really as close as the scope will focus/have zero parallax will work. 

Thanks.

But if I were going to take this to, say, the range, how would you guys handle making sure it was 100% level?  A steel plate or i-beam or vise are great, but if the table or bench isn't 100% plumb, it the apparatus would need to be shimmed.  I'm hoping the four springs on each corner will do the trick.  Maybe mount a cheap vise to that?  But I have a cheap vise in my garage and, even when locked down, it shifts ever-so-slightly (Z axis)

Well there is no point in doing at the range, it isn't even on a rifle. 

I used a 6' ruler mounted plumb on the fence across the yard, then just rotated the scope in the mount so the reticle was plumb, the rest of you rig doesn't need to be level just the reticle does.

This is what I  used, you can resolve to very small increments, everything is big and bold easy to read.

https://www.amazon.com/dp/B0008JF0SU?tag=vglnk-c102-20


I mounted it about 13yds away( actually very carefully measured the distance from ruler to turrets).

Record position, turn turret 5 mil, record position, turn turret 5mil, record position, go back to previous positions, should be the same, repeat etc.

So now you have the distances the reticle actually moved down to fractions of an inch and how much you turned the reticle.

So say your turrets were 24' 5 3/16" from your "target", so that is 8.1441 yards.

Now take 3.600 x .081441= .2932" per mil
So .2932" x 5 mil = 1.466" per 5mil which is 1 15/32 " . The ruler is marked down to 1/16ths if I recall it is easy to see half way between the 1/16 marks so you can get very accurate.

Of course the closer you are the more precise you have to be reading your ruler.

Definitely gotta pick up one of those rulers.

True about the level reticle, but I was hoping to use the rig for double duty, also mounting a scope completely level in rings and then transferring it back to the rifle.

Yeah the mount and upper and scope I was using was all going together.
 I mounted a rail level to the upper, shimmed the vice so the upper was level then made the reticle plumb, tightened it down and mounted my scope level. It worked slick.

The method I used told me the scope error was  - 0.7% of actual, later I did a tall target test at 100yds which told me the scope error was -0.6% of actual, so damn close to the point of the difference being in the noise. 

I  later confirmed this at long range, with the -0.7%  tracking error in my ballistic solver the drops were perfect.

Seems like you could check quite a bit I wonder how often scopes would track differently under recoil.

They shouldn't track any different when exposed to recoil unless something is broken or the scope is junk like the Athlon I tested.

From my initial mistakes.......

You have to make sure all parallax is removed since it is more difficult to position you eye in the same place without a stock.

Everything has to be very solid, any movement pretty much makes the test pointless.

Unless you are mounted to solid concrete, do not lean on or rest any part of your body on the bench the scope is mounted to.

Mount it at a level that is comfortable to you so you are not inclined rest on the bench or stoop over causing fatigue.

Carefully turn the turrets so you don't  disturb the scope.

What if the mount is not perfectly level at the attachment point?

The rifle doesn't need to be perfectly plumb with the reticle. There is a very small but predictable windage error, depending on severity, one could compensate for if desired. 

I drew this up to illustrate the error at different rifle cant (plumb reticle) amounts on a 2" scope mount height. A higher scope will have more error, a lower scope less.

Am I reading that right that a 15 degree cant (which is HUGE) only creates 1/2 MOA of error?  And that's regardless of range or the amount of elevation dialed??

This sounds like a great reason to make a fixture and shoot at different fixed angles to see the difference at different distances.  Sounds like a winter project!  Has anyone done that before?

Yes, keep in mind that is with the reticle being perfectly plumb. A Canted scope is different than a canted rifle with a plumb scope.

The only thing going on here is the bore is offset to the left or right of the centerline of the scope. So when you zero at 100yds you have involve some windage to get that zero, that little bit of windage will continue on to the opposite side from the 100 yard zero at that angle(moa) all the way out.

Just think if you had the 2" height scope mounted plumb at the 3 o'clock position instead of 12o'clock, at 100yds theoretically the impact would be 2" to the right, to get your zero at 100yds you would have to adjust the windage 2". Now past 100yards the bullet would continue on the 2 moa path to the left all the way out. The elevation would still be perfect because the scope is plumb but the windage would have to be compensated for.

Might find something like a precision grid about 2' x 2' used by sewing hobbyists as a cutting matt.  Hobby Lobby or JoAnn's have them; also Wally World, and your local fabric or quilter shop.   Maybe costs $30?

Best solution is a boresighter with collimation grid.  Best gun tool I ever bought.  Assures correct mounting of scopesight, allows diagnosis of problems, enables you to restore a zero, if you kept a log book with grid coordinates of your various handloads.   The Bushnell 74-3333 has a 160moa grid, 40 in ea quad from the central line.  1 box is 4moa in size.

Even more important, using a collimator-boresighter enables you to know if your scope mount is centered over the bore.  Worth owning for this if for no other reason.