Tall Target Test Adjustment question

[BjornF16]

Performed tall target test to prep for hunting trip…first time in field for rifle and scope.

Test: 100 yards, 7.5 mil adjustment (should equate to 27”).

My results from 2 rifles below.

Questions:
1. If 7.5 mil group is to the right of plumb line, which way do I rotate scope?

2. Does 1” right at 100 yards equate to 9” right at 900 yards?

3. For left target below, do I need to make adjustment?

For #1, my initial thought would be to rotate CCW, but the more I think about it I believe it is opposite (i.e. rotate CW).

 

[Wapiti1]

1. Counterclockwise.
2. Yes. But just the center of the group. Individual hits will be in an increasing cone around the group center. The diameter of the cone is dictated by the group size at 100. A 3 shot group isn't telling you the whole story on that, though.
3. Maybe. I would repeat the test with 10 shots at each before I made an adjustment. Seems like you are a little right in both groups, so your 100 yard zero looks a little off.

Jeremy

 

[Lawnboi]

Good rule of thumb…. Never adjust anything off a three round group.

I feel live firing can confirm it, if you know your rifle/cone of fire, are a sound shooter, and use a large sample size. I also understand that a static mount may be a better tool for specifically assessing static scope function.

Also before even messing with any test I’d confirm your scope is leveled correctly and your using some sort of level. Lots of people level with cheap tools and not off gravity.

 

[BjornF16]

Guess I should have given more details of what I’ve already done and what my objectives for tall target test are.

I’ve already performed tracking tests on both scopes. Mounted in gun vice on rifle, vice weighted down with sandbags. No issues noted given short range indoors and less than perfect graduations for the short range.

I’m not concerned about rifle cant. I’ve leveled rifle on two axis and installed level on scope. They match as much as bubble level can given their limfacs.

I’m not concerned with scope reticle cant. I don’t use reticle graduations as BDC.

What I’m primarily concerned with is scope cant. With rifle as level as I can hold it (referencing bubble level on scope), when I dial for range does it track vertically or is there a horizontal component?

Aligning reticle with plumb line is great for BDC, but doesn’t really tell you much when dialing since they are rarely in perfect harmony. Same with using bubble level on top elevation turret. In my case, my first post had turret level just ever slightly CW cant when I checked it post shooting. I’m positive I checked it as level before torquing screws during installation, but that torquing process must have induced some minor cant that I didn’t catch.

As far as my groups on first post, I’m fairly confident in the 6XC groups. I can’t say the same for the 6.5 CM.

Range is tape measured 100 yds to the muzzle.

I adjusted the 6XC and ended up slightly on other side of plumb using 10 mil elevation. That should be 36.02” at 100 yards, or 36.25” at 100.667 yards (24” muzzle to center of scope). 8 shot groups were 36” apart.

This afternoon was 90°F…had some significant mirage on last 6 shots (2 at 10 mils; 4 at 0). Those last 6 shots were right most holes.

 

[Wapiti1]

At this point, its time to stretch it out and see if errors show up.

Jeremy

 

[BjornF16]

At this point, its time to stretch it out and see if errors show up.

Jeremy

Which is what started this … last weekend had significant right drift shooting 550-950 yards (108 ELD-M)…but also had about 5 mph crosswind from left.

So brought it in to 100 to eliminate wind.

At 765 yards, had 1.0 mil drift. Was expecting 0.6 with crosswind and spin drift.

 

[Lawnboi]

So your attempting to find reticle cant if I’m understanding you. In a perfect world the reticle lines up with the turret. Is your reticle plumb? If so can you hold over and shoot? Seems a more simple test would be to shoot a holdover with a plumb reticle next to a dialed group.

Did you find anything in the static test?

When shooting where a tenth makes a difference at a hundred conditions can surely have an impact including mirage.

In the past at distance when I started having problems it was usually because I used a bullet from the red box when it should have been one from the yellow one.

 

[BjornF16]

Initial install I had plumbed the reticle against plumb fence post which nearly matched level turret top (bubble between the line but very slightly favoring one side).

In the process of torquing ring screws, it looks as though I induced some CW cant which I didn’t catch after torquing everything down. Found this after shooting first tall target test.

 

[SomeJackassOnAForum]

You never want to be zeroed right of POA. slightly left will build in forgiveness for spin drift.

 

[BBob]

install scope into rings such that the level on the scope tube is level when the rifle is naturally "shouldered".

People just don’t get this for some reason. Everybody wants everything perfectly vertical and level and force themselves into non natural positions.

 

[General RE LEE]

6. install scope into rings such that the level on the scope tube is level when the rifle is naturally "shouldered".

Shouldn’t the scope level match a rifle that is leveled in a vise vs naturally shouldered? I’ve found when I naturally shoulder a rifle I induce some rifle cant.

 

[General RE LEE]

No.


This is the “why” behind my “no” answer above.

It’s far more important that the reticle tracks vertical than to have the reticle run exactly through the center of the bore & potentially cant the entire system, particularly in the context of hunting/practical/field shooting. If you dial & hold over, then reticle cant within the scope also matters.

View attachment 442163

Cool and thanks for the illustration. Sweet handle BTW, why aren’t you at your post lol

What’s interesting is when my scope is level and I shoulder my rifle, the reticle seems my eyes to have a cant to the left.

I leveled my rifle in a vise and then leveled my reticle off a plumb hanging from the wall and the flashlight method.

 

[BjornF16]

Forget all the bubble levels you used on your rifle and scope. Pull them off.

Stop wasting time & ammo live firing.

1. Pull the scope from the rifle & static mount the scope.

2. Put up a calibrated chart at a known distance to your turret - preferably plumb & level the chart.

3. Get your crosshair lined-up with the plumb & level chart and make sure you resolve parallax.

4. dial elevation

(I'm skipping the part to check tracking). Does the crosshair move exactly vertical along the plumb line, or does it veer to one side? If the reticle travels vertical move to step 5. If not, see sentence below.

If it's veering off to one side, is it consistent, and is it what you would call tolerable? If it's not consistent or within what you consider tolerable, send the scope in for warranty. If yes, rotate the scope so that the center of the reticle travels vertical along the plumb line, and move to step 5.

5. install level on the scope tube while the scope is set for the center of reticle to travel exactly vertical.

6. install scope into rings such that the level on the scope tube is level when the rifle is naturally "shouldered".

Sounds like an optimum practice, unfortunately I don’t have a stand-alone scope static mount. I’ll research making one in the future.

What I can do (as stated earlier) is mount the rifle system in a solid gun vice and run the turrets, which I did again yesterday afternoon. Checking against a plumb fence post with the rifle level, remounted scope level to rifle and parallax removed (top diagram in Post #14), the reticle runs true throughout its full range of travel.

Edit: It also coincides with level when “naturally shouldered”. /edit

I can’t ask for better than that.

Stretched her legs today out to 965 yards and the “issue” I induced earlier (scope canted) appears to be resolved. Slight crosswind (variable 2-6 mph) and calculated wind holds were very close (within .1-.2 mils) at 665-965 yards.

Thanks for all the answers and edubication…