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Scope adjustment for 100 yards

Posted: Fri Apr 18, 2008 6:47 am
by Telecomtodd
I'm using an A-1913 with a Nikon Monarch 6-24x50SF target scope with 1/8 MOA adjustments, and using an Anschutz 6811 mounting plate on the sight rail. I've finally gotten the stock and the scope adjusted to the point that I shot a -1 at 50 yards last night. However, I'm not able to adjust to 100 yards; I run out of windage. Last week at a match I ended up having to shoot at the 9-ring at 12:00 in order to have enough elevation to hit the target.

When I boresighted the scope at 50 yards, I started from a center point (160 clicks from the bottom). However, when I got to the range and actually started shooting with it, I had to run the windage back up towards the top. Set for 50 yards I end up having only 40 clicks of elevation available, and I need 72.

Common sense would suggest shimming the back mount over the rail with something. Someone suggested tin foil to me last night. Anyone have a better suggestion before I take it all apart and wind up chasing my tail? Thanks!

Todd Ellis

Posted: Fri Apr 18, 2008 8:10 am
by jrmcdaniel
Your problems are common to field target shooters who use air rifles to shoot 10 to 55 yards. Usually, it is the 10 yards that cause the problem with running out of clicks. The approach we use is to shim the mount or get mounts designed for the droop.

BKL makes mounts with built-in droop. Highly recommended. I think Weaver makes some mounts with rotating off-center scope clamps to do this, too.

You may be able to reverse your mounts and get enough droop compensation. Sometimes, one mount is a bit higher than the other.

To shim the mounts, zero the scope elevation, loosen the mounts and put some shim material (strip cut from a soda can works well) under the mount at the gun (do not shim at the scope or you will dent the scope). Take a shot or two at your zero distance (for air rifles, this is usually 25 to 30 yards -- for .22LR, it would be 50 yards or so) and see if you are close in elevation -- if not add another layer of shim. You won't be able to shim a lot and still get the mount to work. If you are close, you can then use the elevation knob to do the rest of the adjustment.

Best,

Joe

Posted: Fri Apr 18, 2008 9:53 am
by Marcus
Are your scope mounts on backwards? I really mean is the front one on the rear? and rear on the front? That just doesn't sound right that you should run out of elevation at 100 yards with what sounds like a normal setup.

Posted: Fri Apr 18, 2008 10:00 am
by Telecomtodd
Well, I don't believe so since the 6811 is indented to accomodate the right side receiver opening. I have it lined up with the front edge of the receiver opening. I did NOT order the left hand rail adapter.

Posted: Fri Apr 18, 2008 10:13 am
by Marcus
I meant the rings that clamp to the rail and hold the scope. The short one should be in front.

Some scope mounts "the rings" are also adjustable for windage having tigtening screws on both sides where they clamp to the rail. Your initial posting was a bit confusing in that I believe you were mixing the terms windage and elevation.

My initial reading made me think you were having trouble with getting enough elevation, but on closer reading you may also have some problems with windage.

Posted: Fri Apr 18, 2008 10:40 am
by Telecomtodd
OK - shame on me for posting these messages while enduring a 3 hour conference call!

I meant elevation, not windage. You are right on the money there.

I took the scope out of the rings and removed them from the 6811 rail. They are exactly the same dimensions. I took the top of the ring off so the ring bases were the only thing being measured, and I used my electronic caliper to measure .561" from the bottom of the base where it rides the rail to the bottom of the hollow part where the scope rides the ring. I put both rings next to each other on a flat table and it's obvious they are the same dimensions. Now to put all the screws back in...

I guess I'm back to a soda can shim?

Posted: Fri Apr 18, 2008 11:03 am
by Telecomtodd
I found a non-obvious solution!

If you look inside the ring, there is an insert at the bottom. Both had the insert so that the flat part was on the bottom. I unscrewed the hold-down screw, and the insert slid out. Turning the insert upside down, there's a small .09" nipple. This then rides on the rail, effectively lifting the rear end of the scope. Problem solved!

Todd Ellis

Posted: Fri Apr 18, 2008 1:32 pm
by Guest
I never saw the plug thing before.
On all of my 100 meter silhouette rifles, I have to put a shim from a credit card in the rear ring. Zero is at 40 meters, and it is about 10 - 12 minutes to 100 meters. I usually use BKL or Beeman high rings, and Leupold or Bushnell 4200 scopes.
For the silhouette smallbore a general rule of thumb is:
40 meters - 0 (minutes)
60 meters - 2.5
77 meters - 5.0
100 meters - 10
Ter