Windage POI change ...
 
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Windage POI change between 15&30 Yards  

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truck-driver
( @truck-driver )
Joined: 11 months ago
Posts: 26
2020-01-28 10:43:59  

I have a Diana 54 177 TO1 set up for 12 fpe that I sighted in at 15 yds off a bench with bag rests front and rear. Scope is a Sightron SI FT 4-12X40 AO. SIghted in with JSB 8.44gr Exacts 4.53" dia.

When I shoot at 30yds using the same center target hold my windage changes 13 cm to the right of center. What's up with that? 

The elevation also changes but that was expected and is about 12 clicks difference between 15& 30 yds.


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nervoustrigger
( @nervoustrigger )
Joined: 2 years ago
Posts: 218
2020-01-28 11:44:45  

Usually this kind of discrepancy is caused by cant error.  Either scope cant which deals with the scope being twisted in the mounts, or gun cant which deals with tilting the gun while shooting.

Having said that, 13cm (5in) of lateral shift between 15 and 30 yards is an awful lot.  Might be a good idea to first check to see if something is causing the axis of the scope body and the axis of the barrel to diverge.  For this amount, you can probably spot it by eye but you can be more confident in ruling it out if you will temporarily clamp a length of dowel or a piece of pipe in the scope mounts and see if it and the barrel track closely together.

With that done, turn your attention back to the two forms of cant.  Refer to Scotchmo’s thread for how to deal with them:
https://www.gatewaytoairguns.org/GTA/index.php?topic=72099


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pluric
( @pluric )
Joined: 2 years ago
Posts: 631
2020-01-28 12:01:40  

Do you have another scope/ring set up to try? It's not often but I have had differences between optics.

 


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K_sqrd
( @k_sqrd )
Joined: 2 years ago
Posts: 23
2020-01-28 12:31:53  

Another cause for the shift in POI could be your AO. I had a couple of Vortex Crossfire II's where

changing the AO would cause the POI to shift by about 1.5 inches in the 10 to 50 yard range. If you have

another scope, give it a try and see what happens.


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truck-driver
( @truck-driver )
Joined: 11 months ago
Posts: 26
2020-01-28 15:54:16  

Thanks for the replies everyone. I messed up in the first post and read the scale wrong I think it's

13 mm not centimeter probably 9/16", I'm not good with metrics.

NT thanks for the link.


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truck-driver
( @truck-driver )
Joined: 11 months ago
Posts: 26
2020-01-31 12:41:49  

Just to let you know I listen and take advise I read the link and changed the mounting procedure I was using.

I hung a plumb bob on a tripod and aligned the reticle in the scope. Drew a  cross on plain paper and set it at 25 yds making sure the cross was level and square set the rifle up on a bench and sighted the scope in keeping the reticle square on the cross. Once the scope was zeroed I moved the target to 15 yds and checked to see if there would be a windage poi change five shots 1" low but right on the vertical line.       Success I had solved my problem.

Just for giggles I checked the scope and rifle to see if they were level or square with each other and they weren't. The scope isn't level with the spirit level setting  on the scope turret.  Hmmm new lesson learnt. The action isn't setting square in the stock either so the inlet cut is also off.

Amazing what you can learn when you square everything to the Earth's center and straight gravitational pull.

I must have gotten lucky with the other two rifles and scopes since I haven't seen the windage poi change with them but I plan on checking them to make sure.

Thanks for the Help.


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