Author Topic: Scope installation tool—NO cant!  (Read 545 times)

Alan

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Scope installation tool—NO cant!
« on: July 28, 2018, 11:00:37 AM »
Arisaka makes a tool which makes installing scope a lot easier than using levels. It costs about $35 on Amazon (see photos). It assumes that the mounting surface (picatinny or 11 mm) is perpendicular to the bore, which it should be if machined into the receiver. I bring this up, as once again I read about folks who just can't get the cant out! This solves that issue once and for all.

That is, scope to gun. If you're canting because of faulty vision, an external level mounted to the rail, is the best bet.

« Last Edit: July 28, 2018, 11:09:22 AM by Alan »


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Alan

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sixshootertexan

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Re: Scope installation tool—NO cant!
« Reply #1 on: July 28, 2018, 12:08:02 PM »
Pretty cool. I've been using a adjustable machinist parallel for years. Never liked trying to keep a gun level while keeping the scope level method.
CCS 2300, CCS 2400, Custom Built Regulated .25, Custom Built PRod Clone, .308 Bullet shooter, XS46U .177, Custom regulated .177, 850 Hammerli .177

rsterne

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Re: Scope installation tool—NO cant!
« Reply #2 on: July 28, 2018, 04:04:18 PM »
Slick tool for insuring that the scope is parallel to the top of the receiver.... however, unless the scope is centered exactly over the bore, it will NOT install the scope properly to insure no horizontal offset in the POI occurs in shots which require holdover.... which is the whole problem that CANT causes.... Consider this diagram....



If the scope is not centered over the bore, the Ariska device will insure that the scope is mounted as per drawing "A".... However, the PROPER was to mount an offcenter scope is shown in diagram "B".... Once so mounted, then you must then hold the rifle as in diagram "C" to insure there are no issues with scope cant....

Here is a complete analysis of ALL the possible types of cant error.... and what happens to the POI when shooting closer and further away than the zero distance.... For simplicity, the zero is assumed to be at the top of the pellet trajectory (single point zero)….



Mounting a scope as in diagram "A" on the first drawing will cause your shots to have either error "F" or "G" on the second drawing.... depending to which side of the bore the scope is offset....  There is only ONE proper way to install a scope, and that is with the vertical crosshair of the scope intersecting the center of the bore, as in diagram "B" on the first drawing.... You then hold the rifle so that the crosshairs are vertical and horizontal when shooting.... and the path of the pellet due to gravity will track along the vertical crosshair.... ANY other way of mounting the scope to the rifle.... or holding the rifle/scope combination.... will result in one of the errors in the second drawing.... NOTE, the stock of the rifle, and the top of the receiver, may not be vertical when the scope is properly mounted and the rifle is held with the crosshairs level/vertical.... in fact that will only occur is the scope rings are centered laterally over the receiver....

Bob
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Alan

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Re: Scope installation tool—NO cant!
« Reply #3 on: July 28, 2018, 04:50:49 PM »
You are correct!

When mounting scope on modern rifles (air or powder), I assume the mount is properly centered with respect to the bore. I know that isn't always the case, but I also believe it is a rarity when it is not.
« Last Edit: July 28, 2018, 04:59:11 PM by Alan »
  • Roswell, New Mexico
Alan

I have an Omega compressor. If you're a fellow Guild member, and you pass through Roswell, NM, I'll fill your portable tank as a courtesy.

rsterne

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Re: Scope installation tool—NO cant!
« Reply #4 on: July 28, 2018, 07:11:52 PM »
IMO, with the cheap dovetail rings we often purchase, I think the rarity is having the scope directly above the bore, rather than not.... My Hatsan, with Hawke rings, was wayyyyyyyyyyyy off, and suffered from this exact problem.... When I used the mirror method to make sure the vertical crosshair bisected the bore, the problem of shooting one side of the crosshair at close range and the other side at long range disappeared....

For those that have never used a mirror to align the scope with the bore, here is the procedure....

1. Place a vertical mirror 5 yards from the muzzle, and focus the scope at 10 yards.... Scope mounted in rings but loose enough to rotate.... Set the scope at maximum magnification.... This works best if the scope is first centered optically (counting clicks is close enough)….

2. Look at the reflection of the gun through the scope, and rotate the scope in the rings until the vertical crosshair bisects BOTH the muzzle and the objective bell of the scope.... Carefully tighten the rings while maintaining this alignment....

3. When you shoot, make sure you hold the crosshairs level / vertical, even if that means your gun is tilted....

If you wish to use an external level attached to the scope, after mounting it loosely, align the crosshairs with a plumb line or level.... Set the level so that the bubble is centered and tighten it in place....

Bob
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Alan

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Re: Scope installation tool—NO cant!
« Reply #5 on: July 29, 2018, 04:48:06 AM »
You brought up two other issues—poorly-made rings and/or poor machining. I'll give you another one—poor scope manufacturing. I have a Hammers scope with a built in level. That "level" is off by about half a bubble, and there is no external adjustment. One of the two UTGs I have is off a bit as well.

As I said above, you have to assume things are machines correctly (aligned?-assembled?), which they are most of the time. Playing the Devil's advocate... When they're not, do you adapt by using your technique? Or do you fix the problem? I think we both know the answer.
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Alan

I have an Omega compressor. If you're a fellow Guild member, and you pass through Roswell, NM, I'll fill your portable tank as a courtesy.

sixshootertexan

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Re: Scope installation tool—NO cant!
« Reply #6 on: July 29, 2018, 08:52:38 AM »
This parallel method only works on about half the guns I own. The ones with the round receivers such as the 2240 style guns I just do my best to get them level.
CCS 2300, CCS 2400, Custom Built Regulated .25, Custom Built PRod Clone, .308 Bullet shooter, XS46U .177, Custom regulated .177, 850 Hammerli .177

rsterne

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Re: Scope installation tool—NO cant!
« Reply #7 on: July 29, 2018, 09:51:27 AM »
I twist the scope in the rings until the vertical crosshair aligns with the bore.... It's such a simple fix, compared to the cost of buying expensive rings, and you have to do it anyways to check things.... so why not?....

I am blessed with a very good eye for holding things level, so I have never bothered with a scope level when shooting....

Bob
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Monkeydad1969

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Re: Scope installation tool—NO cant!
« Reply #8 on: July 30, 2018, 10:27:24 PM »
Hey Alan, nice find.

Joe
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