Leveling the Scope Reticle for Long Range Rifles

[bruce_ventura]

DocB,

Are you saying the scope is rotated counterclockwise 2 degrees or the base is angled off center 2 degrees?

- The scope is rotated counterclockwise relative to true horizontal. In practice, the anti-cant indicator is rotated clockwise.

After you dial up to 1000yds, are you still shooting the same POA on the same 100yd target as the first group you fired?

- Yes, the impacts will land far above the first group.

 

[paphil]

Yes , the scope itself is canted left( counterclockwise) and with the scope in that position, the level is installed reading level. It is about a half a bubble off plumb! This can be done in the shop with a gun or scope vice and a vertical line about 25 yards away(far enough to get a focused image with the scope. Make a vertical line with a carpenters level. Now, I calculate the value of 2.5 degrees at a height of 24 inches. At this height, one degree is about .42 inches so 2.5 degrees is about one inch.( formula pii X diameter in inches divided by 360 degrees) Now, from a point, on the line measure up 24 inches and left 1 inch and connect the two points. Now, with the scope/gun in a vice, allign the scope with the canted line and install the level on the scope. The scope is tilted 2.5 degrees and the level stays level. It would be easier if the level screws were on the top instead of the bottom! The next step is getting the gun held in a comfortable position and then rotating the scope and level untill the horizontal is affirmed by the level. This is a custom set up for those that find it difficult to keep the gun from canting as indicated by the level. Most guns I do are level and square and the shooter must make those adjustments as he sees fit. Some don't want to pay that extra $50.00 for a level but it will make all the difference in the world! One word about spin drift, with the 2.5 degrees cant, on the 100 yard target, 1000 yards of elevation is 23 moa and 1500 yards is 51 moa so it is allowing almost 30 inches for spin drift at 1500 yards while only 10 inches at 1000. It is hard to get completly calm conditions to test, but to the best of my ability, this seems to work. another thing to remember is that after 1000 yards, everything goes south and all varibles are greatly increased and Coriolis must be allowed for. Hope this helps!

 

[paphil]

Another thought here, don't get discouraged reading all of this stuff! First, learn good skills at short ranges with small guns. Shoot enough , practice enough, to know if a gun shoots well and also to know if YOU shoot well! As you gain experience, all these other things will fall in place. Long range is a great sport and it is great to have guys like Bruce to help define the science of ballistics. Play with a smallbore and scope to see what happens when you try these ideas promoted in this thread and other great threads on this forum. And, most of all, don't believe everything you read! Think things through before doing things that could be dangerous! Have fun shooting!

 

[DocB]

Another thought here, don't get discouraged reading all of this stuff! First, learn good skills at short ranges with small guns. Shoot enough , practice enough, to know if a gun shoots well and also to know if YOU shoot well! As you gain experience, all these other things will fall in place. Long range is a great sport and it is great to have guys like Bruce to help define the science of ballistics. Play with a smallbore and scope to see what happens when you try these ideas promoted in this thread and other great threads on this forum. And, most of all, don't believe everything you read! Think things through before doing things that could be dangerous! Have fun shooting!

I asked earlier and am still curious, why do we use 'right hand' barrels in the northern hemisphere instead of 'left handed' ones?

Doc

 

[paphil]

I don't know of any barrel makers that make left twist but I've heard of some European guns that have Left twists. The problem is the same only in the opposite direction. Spin drift is not the same in all bullets and calibers but as best as I can tell, it is between 6 and 12 inches at 1000 yards depending on the twist speed and the shape of the bullet. Coriolis is an addition to or subtracted from the spin drift depending on direction of flight of the bullet and the time of flight. Shooting east will cause the bullet to hit high because the earth and the target are falling. about 3 inches at 1000 yards with a 7mm vld. shooting west is just the opposite . The earth and the target are rising and the bullet will hit low, again about 3 inches. Shooting north and south is still a question in my mind, but if the target is moving with the earth, it would move left to right looking north and right to left shooting south. Still about 3 inches for a 7mm vld with mv of 3000 fps. All of this is very hard to prove due to other environmental issues but I'm sure there is a mathmatical solution. This is all based on time of flight so slower bullets and longer shots will have more effect. Maybe there is someone with artillary backround that could post their thoughts! Not many guns shoot well enough to tell these small effects but when you add them all togather it makes those shooter programs look pretty handy.

 

[paphil]

Spin and Coriolis Drift
this is a good link by Brian Litz

 

[CanardNoir]

Another thought here, don't get discouraged reading all of this stuff! First, learn good skills at short ranges with small guns. Shoot enough , practice enough, to know if a gun shoots well and also to know if YOU shoot well! As you gain experience, all these other things will fall in place. Long range is a great sport and it is great to have guys like Bruce to help define the science of ballistics. Play with a smallbore and scope to see what happens when you try these ideas promoted in this thread and other great threads on this forum. And, most of all, don't believe everything you read! Think things through before doing things that could be dangerous! Have fun shooting!

So far, this has been the most reasonable advice offered.

Remember, it remains very difficult to replicate decades of experience within 5-10 paragraphs of written instructions.

 

[lyotehunter]

i use the plumb line to make sure everything is level.i then go to the range and put a 36"piece of white paper on my target backboard butchers paper works.i take my level and draw a vertical line up the target put a dot in the center,then i go 200yds and click my scope up the target as far as i can staying on the target.check the level with the plumb line ,your bullets should follow the line up if everything is working you should have a bubble on your scope to make sure you hold the gun level also.

 

[ultraedge]

Mark Chanlynn of Rocky Mountain Rifle Works makes lefthand twist barrels. Gary

 

[Byrnesy]

Ok so some comment and questions from down under.

Firstly with reference to previous comments to Thomas Haugland's video.

I rate myself able to judge level pretty **** well. Now I will qualify that statement in saying that I wont attempt a challenge of it through a scope but in other trades like situations. And I know a few other top tradesman that can do the the same, but it is by far not the majority that can visually judge level.

Further to that video, Thomas goes on to check the tolerance of the ACD against his digital level and finds exactly what I have found and thought many times; that some spirit levels are a WOFTAM as the marks are way wider than the bubble. Instrument need to be precise. We wont accept a scope that maybe somewhere between .2 and 45. MOA per click so why make ACDs that have a about a 3 degree tolerance?

Secondly, I have been reading this thread and associated article as I am setting up a Howa 1500 in a Boyds in 243 as a entry in to long range. It may see a truing job and re-barrel down the road when my abilities progress.

And yes, as a hunter for 22 years their are a few things in the article I have never thought about because I haven't had to.

But if Bruce could answer a question that would be great. Dependent on machining errors, mounting systems and corrections, from what I have read I may end up with the reticle canted to get the reticle over the bore (Scope is a VX3 4.5-14X40 CDS) Correct?

Now if this is the case, purposely canted, then when I fit the ACD to the scope tube, I fit it on 'Level' with the action leveled, dont I?

Thanks and the threads are always thought provoking which I enjoy too.

 

[bruce_ventura]

Byrnesy, yes it's possible to have the scope correctly aligned to the bore and end up with it "canted" (not parallel) to the action. In this case, align the anti-cant indicator so that it is level when the scope is level.

 

[Byrnesy]

Bruce some feedback.

Shot the Howa today and it went well. Will post up a thread during the week.

So firstly, both me and my mate , who is a very accomplished shooter, both thought we were holding the rifle level but alas, no, not according to the ACD.

On setup the rifle was levelled then a plumb bob was hung 20 metres out in front disecting the bore. The scope was then placed in the rings and the reticle leveled. And wow the reticle was dead inline with the plumb line without moving a click. Scope was then removed and rings lapped. Even on sighting I only had to move 3 clicks left, 1/4 MOA.

SCope is a VX3 4.5-14X40 CDS and the mounts are Talley Lightweights. Barreled action is a Howa 1500 in Chrome Moly fluted varmint in 243. All sitting in a Boyds Thumbhole Varmint.

 

[CRaTxn]

At what range[distance] was "sighting in" done. How many wind flags or indicators did you have out?
What_____ hand twist is the barrel? What magnetic direction were you shooting? Were these "cold barrel" shots? Which way does the water swirl when you flush the loo or "terlet" as Archie Bunker said?
Have you read the whole post?

 

[Byrnesy]

At what range[distance] was "sighting in" done. How many wind flags or indicators did you have out?
What_____ hand twist is the barrel? What magnetic direction were you shooting? Were these "cold barrel" shots? Which way does the water swirl when you flush the loo or "terlet" as Archie Bunker said?
Have you read the whole post?

Sight in 100yds

4 winds flag @ 20 50 75 and 100.

Right hand twist

East

Combination of Cold and warm

Water Swirl is Clockwise

Yes I have read the whole thread.