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# Reticle Perpendicularity by Darrell Holland

#29
09-24-2008, 12:20 AM
 Silver Member Join Date: Jun 2008 Location: christchurch, nz Posts: 329
Re: Reticle Perpendicularity by Darrell Holland

ok i think i see where mkollman74 is getting messed up. lets say we take a rifle and level it with a level on the action somewhere. then we mount a scope on it and set the normally horizontal xhair as verticle. so now we have a scope that is at 90 degrees to the rifle. lets say the scope is 1.5 inchs above the center of the bore. then we cant the gun to the right 90 degrees so the x hairs in the gun ( the usual verticle one) is verticle. assuming that the bullet path is straignt for the moment and the line of sight is parallel. then the bullet will hit 1.5inchs left of line of sight at any range.
now we all know that bullets dont travel in straight lines other wise id be shooting bunnies at 1km. if the bullet path was horizontal with the line of sight at 100m then the impact point would be 1.5inch left and 0 up and down. then go to 200m and the impact point would be 1,5 left and lets say 2 inchs down. then at 300m impact would be 1.5 left and lets say 6inchs down. and so on. the up and down could be corrected for, but the bullet path would always be 1.5 left. this is where the issue lies. no one wants there bullet to always be 1.5 left.
so with the same scope rifle set up and sighting in at 100m we would dia the scope across 1.5 inchs so that at 100 the line of sight on bullet path would cross.. so this would be making a triangle with the shortest side beind 1.5 inchs(distance between sight and bore) the other side of the triangle 100m and the last side slowly slopping into the point. then at 200 the impact point would be 1.5 right and x low. at 300 would be 3 right and x low, at 400 would be 4.5 right and x low at 500 would be 6 right and x low and so on. this is because the bullet was sent on its way crossing the sight path on a left to right course. sighting in at 300 for example would greatly reduce the effect.
i think that is the confusing part explained. well unless i confused myself while writing this.
so the key is to just have the scope level and the bore axis verticly under the x hairs and ensure that the scope is level when shooting. cheers
#30
12-16-2008, 10:43 PM
 Junior Member Join Date: Sep 2008 Posts: 24
Re: Reticle Perpendicularity by Darrell Holland

All I have to say is great article. I tried it out and it worked absolutely awesome.
#31
03-07-2009, 12:09 PM
 Bronze Member Join Date: Jan 2009 Location: Mich. Posts: 76
Re: Reticle Perpendicularity by Darrell Holland

Quote:
 Originally Posted by mkollman74 I had basically this same question. One further question: Am I reading this wrong or is the suggestion to mount the scope perpendicular to the bore of the rifle? I have never understood how you can position anything in a relationship perpendicular to a round object. Since it is round, it really has no X or Y axis does it? Level is level, and plumb is plumb, right? If a cylinder is rotatated, up and down don't rotate with it, they are fixed in space. The bullet still exits the barrel, and gravity still pulls straight down on it. Any wind still deflects it to the same degree. I do not mean to appear argumentative, I just don't understand, and wish to. I want to be better at this long range game. So, if the barrel is round, and I naturally cant the rifle, why shouldn't I mount my scope so that it appears perpendicular the horizon to my eye using my natural hold? The canting only rotates the barrel along its longitudinal axis, the bullet still travels the same path, right? If I need extra elevation, and I dial it in or hold over, the impact will still travel in line with the vertical wire of my reticle because I am moving the canted rifle up to adjust to the new point of aim. The center of the barrel still moves in the same direction - up. Rotating the barrel by canting doesn't change the direction by which gravity pulls the bullet straight down, it doesn't alter the ballistic arc. So, I am still confused as to why a naturally canted hold on the rifle would produce an off shot unless the rifle itself were held perfectly perpendicular to the horizon for that shot. If I cant the rifle but have mounted my scope so that even with that cant its vertical wire is parallel to a plumbline, shouldn't that be OK? I can see where dialing elevation into a scope mounted at an angle to a rifle held perfectly plumb would produce a horizontal dispersion. But holding a rifle at a slight cant and mounting the scope so that its reticle is parallel to a plumb line even given that cant should have the same effect as an offset type of scope mount such as was used on some M1s during WW2 by military snipers. In effect you are holding the rifle with the scope slightly to one side. Am I wrong? I barely passed high school geometry... Again, no flames, just curiosity and respect for the expertise on this forum.

I use a Bore Level, all my rifles have a one piece weaver style mount and this works good to level your bore while mounting and leveling your scope to the bore. I can leave this mounted to my rifle while shooting if I need to keep it level for long range shooting. MidwayUSA - B-Square Bubble Bore Level Weaver-Style

Last edited by glockman55; 03-07-2009 at 12:26 PM..
#32
03-12-2009, 05:28 PM
 Junior Member Join Date: Mar 2009 Location: Lewiston, Idaho Posts: 13
Re: Reticle Perpendicularity by Darrell Holland

Wow, thanks for the Great article. I just purchased my second long range gun, this one a remington 700 sps varmit in .308 calibler. I ditched the stock and went with a Bell and Carlson, adjusted the trigger, installed Badger Ordinance Rings and Mount, Harris Ultra-light 6-9" swivel bipod, and a 16x42 Super Sniper scope. I have yet to fire a round down range still waiting for a couple parts to arrive. But after reading this article I will definately try this I think it is very important to have scope perpendicular.
Thanks,
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Hosboss2002
#33
09-30-2009, 09:31 AM
 Silver Member Join Date: Jul 2009 Location: Salmon, Idaho Posts: 392
Re: Reticle Perpendicularity by Darrell Holland

My method for mounting a scope and aligning the reticle is as follows. First I assume that the bottom of the action is perpendicular to the bore. That being said I remove the barreled action from the stock and place it on a level surface with the action supported on a pair of precision ground 1-2-3 blocks and I use a machinist jack set to support the muzzle end of the assembly. With the scope loose in the rings and as close as possible to the location I want it to be for proper eye relief I can rotate the scope within the rings and use a machinist set up square indexed of the same level surface as a verticle reference line. Line the verticle crosshair up with the verticle edge of the square and you are plumb. I've tried putting spirit bubbles on the tops of the reticle caps and on the reticle itself and it's never worked out, at least not to the level of precision that I'm after. I prefer to use machined surfaces to reference off of when trying to maintain parallelism and perpendicularity. All these tools can be purchased from MSC or Enco for less than what you 'd spend on most of the scope leveling gadgets that are on the market.
#34
09-30-2009, 03:17 PM
 Platinum Member Join Date: Jan 2008 Location: Falls Church, VA Posts: 2,728
Re: Reticle Perpendicularity by Darrell Holland

Quote:
 Originally Posted by fj40mojo My method for mounting a scope and aligning the reticle is as follows. First I assume that the bottom of the action is perpendicular to the bore. That being said I remove the barreled action from the stock and place it on a level surface with the action supported on a pair of precision ground 1-2-3 blocks and I use a machinist jack set to support the muzzle end of the assembly. With the scope loose in the rings and as close as possible to the location I want it to be for proper eye relief I can rotate the scope within the rings and use a machinist set up square indexed of the same level surface as a verticle reference line. Line the verticle crosshair up with the verticle edge of the square and you are plumb. I've tried putting spirit bubbles on the tops of the reticle caps and on the reticle itself and it's never worked out, at least not to the level of precision that I'm after. I prefer to use machined surfaces to reference off of when trying to maintain parallelism and perpendicularity. All these tools can be purchased from MSC or Enco for less than what you 'd spend on most of the scope leveling gadgets that are on the market.
wow - that sounds complicated.

Try the easy way.... Wheeler Engineering Level-Level-Level Scope Crosshair Leveling Tool - MidwayUSA
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I'm not gonna shoot here. I'm gonna shoot waaaaaaaay over there!
#35
09-30-2009, 04:22 PM
 Bronze Member Join Date: Jan 2009 Location: Mich. Posts: 76
Re: Reticle Perpendicularity by Darrell Holland

I Agree!!

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