First tall target test...planning

[done111]

I am going to check my scope turret accuracy by doing my first tall target test. I have an 11x17 sheet of paper (actually several) of card stock type thickness. I don't have a good straight edge that long, so I plan to hang a plumb bob and mark 3.6 inch divisions up from the bottom target I'm shooting at, using the plumb bob string as a vertical guide. My scope as you probably guessed is in milrads. Should be able to mark up to 4 mils (maybe a little more) and keep it on the paper, tacking the 17" side of the paper vertical. Instead of trying to draw a continuous line (like I said don't have a good straight edge) I plan to put a sharpy marker dot at the 3.6" distances up from the base target I will be shooting at on the bottom of the paper.

Question to you all is how are you all setting up your tall target test? I could try to mount more paper and try to make it longer but I may be limited by the boards I have to mount the paper to. It would be nice to get more like an 8 milrad range to check in 1 milrad increments. Also, I have a level clamped to my scope clocked with my reticle so I'm thinking I should be able to check if my elevation turret follows the vertical line of the reticle. If it has some cant in it, do any of you adjust your level to compensate? Maybe there is other things I can learn from this test as well that might need to be setup as well?

Thanks for your help, I'm really wanting to get as much as I can out of this test when I do it.

Don

 

[jimbires]

you could adj elevation a couple different settings to check the elevation impacts match the turret settings .


here is a link to an article I've used as a guide .
https://www.longrangehunting.com/articles/reticle-perpendicularity.34/

 

[yukonal]

Stack 1 of those 17 inchers above the other, for a target at least 30" tall.

Search Brian Litz's youtube video on the tall target test.

 

[done111]

I do plan to shoot several different milrad elevation settings, working my way up the the top of the tall target.

 

[Toolbreaker]

Does your reticle have elevation stadia above the crosshairs? If so, you can use one of them to hold for a new zero while continuing to dial up the turrets. As example, dial 4 mil, then use the 4 mil stadia as your new zero and dial 4 more.

 

[chromatica]

Go to Staples and pick up a piece of foam posterboard (30x40). It will give you enough room to shoot 10 milRads at 100 yards.

Check out the description of my tall target test:

http://forum.accurateshooter.com/threads/tall-target-test.3933153/

I am going to check my scope turret accuracy by doing my first tall target test.

 

[jimbires]

Don , if you are close to a auto collision repair shop , stop in and ask for a fender , or hood box . these are way big enough , and the shop will be glad to get rid of a few .

 

[Howland]

A 4' bubble level might be easier and more accurate than a plumb bob. It doesn't matter whether the backboard is level, just the grid. My tall target test is coming up soon and that is my plan.

I also plan on using a thick Sharpie so I can see the grid as I'll be doing it from 400 yards, and adding florescent round dots at measured spots along the grid to correspond to my MOA reticle and turrets. I'm trying to make it simple.

 

[done111]

Update: It was real windy today so no plumb bob could be used. I did however shoot a 3 shot group at a small target very low on the board at 100 yards, then adjusted 8 mils up and shot 3 more. Distance between the groups measured right at 8 mils using my reticle in my scope to measure it. It was also straight up and down, using my scope level to keep my reticle plumb. So i figure my turrets agree well with my reticle. Assuming my reticle is correct, I feel pretty good about the turrets on my Vortex HST (at 18x magnification where milrads of reticle are correct).

Is there a flaw in using my reticle as the measuring stick to determine proper milrad movement of my turrets?

Don

 

[Toolbreaker]

Is there a flaw in using my reticle as the measuring stick to determine proper milrad movement of my turrets?

Don

Hey Don. In my opinion, no. As long as the two agree, that's the important part. Your rifle and optics combo is a closed-loop system that (to a certain extent) only relies on it's own feedback to calibrate with a given, accurate load. That's why I mentioned earlier about dialing up & holding under. If your turret's movement match your reticle subtensions, a shot fired at a certain dial/counter-hold position should print the same POI as what the rifle is zero'd at.

 

[Texas10]

At the local range one day, the O.F. Range Officer talked about how he came up with a brilliant system, and the beauty is you can do it in your back yard.
He took a cinder block and glued a 4x4 to it, screwed a scope rail to the 4x4 and mounted the scope. He also made it adjustable for elevation by mounting the brick to a 2x8 and adding a screw-in type chair footing on the front end. It was all very clever.

A bit of math comes into play here, and a grid is laid out on a piece of paper in one MOA or MIL increments and tacked to an upright at a known distance, measured to the inch from the objective lens.

Set the scope with mount on a firm surface and align with your starting point on your grid. Then just crank the knobs and record the results.

I went home and tried it out on a new scope. Worked beautifully! The scope didn't quite return to zero every time (off by 1/4 min) but the interesting thing was when I hit the max elevation adjustment, the knobs kept turning, but the reticle remained unchanged. Didn't expect that.

I also screwed up on my starting point, forgot the reticle moves (points) downward as I add elevation. DUH!

In the end, I sent it back and bought another scope as the windage knob was pretty much T.U.

 

[Bart B.]

I went home and tried it out on a new scope. Worked beautifully! The scope didn't quite return to zero every time (off by 1/4 min) but the interesting thing was when I hit the max elevation adjustment, the knobs kept turning, but the reticle remained unchanged. Didn't expect that.

Now you know why putting scope adjustments mid point in their range is not the way to zero them to the optical center of the scope which is on the main tube center.

The windage adjustment will probably do the same thing to the right.

 

[chromatica]

Update: It was real windy today so no plumb bob could be used. I did however shoot a 3 shot group at a small target very low on the board at 100 yards, then adjusted 8 mils up and shot 3 more. Distance between the groups measured right at 8 mils using my reticle in my scope to measure it. It was also straight up and down, using my scope level to keep my reticle plumb. So i figure my turrets agree well with my reticle. Assuming my reticle is correct, I feel pretty good about the turrets on my Vortex HST (at 18x magnification where milrads of reticle are correct).

Is there a flaw in using my reticle as the measuring stick to determine proper milrad movement of my turrets?

Don

Use a yardstick to measure the distance on your target. One mil is 3.6 inches, 10 mils is 36 inches, etc.

 

[Barlow]

Get a roll of freezer paper at the grocery store, tear off the length you need. Use the dull side to shoot at. I carry a 6" level in my range box to set up target at the range. Barlow

 

[Texas10]

Now you know why putting scope adjustments mid point in their range is not the way to zero them to the optical center of the scope which is on the main tube center.

The windage adjustment will probably do the same thing to the right.

Waiting.........still waiting, ever so patiently....

 

[Bart B.]

Waiting.........still waiting, ever so patiently....

Step 1:
Put a scope in two V blocks (cardboard box, V's cut in opposite sides, box weighted to stay in place) then look through scope twisting it adjusting E and W until reticle center stays at the same place. Now the scope inner tube is centered (zeroed) in the outer tube.

Step 2:
Count the clicks in elevation up to their stop, record the number, then reverse them back to zero. Count the elevation clicks down to their stop, record the number, then reverse them back to zero.

Step 3:
Repeat step 2 with the windage clicks to their right and left stop then back to zero.

Step 4:
Compare the adjustment limits in all directions from zero obtained in V blocks. This is the optical center and mechanical center of the outer tube that centers in the mount's rings. As shown in all engineering diagrams shown in rifle scope patents.

Or......

1. Put both E and W adjustments midpoint in their range.
2. Put the scope in V blocks (as above) then look through it as you spin it.

What do you do if the reticle center circles about some point?

 

[Texas10]

Thanks for getting back, Bart. Going to try this out.

On the scope in question, which as I mentioned was returned:

1 Couldn't accomplish step 2 as there is no hard stop on turrets except bottomed out, so finding the mechanical center in this case seems unlikely.

2 What to do if turning the ocular causes the cross hairs to orbit instead of remaining centered?