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 Post subject: POI shifting
PostPosted: Sat Jul 08, 2017 11:29 am 
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Joined: Mon Aug 08, 2016 9:58 am
Posts: 18
I'm very new to smallbore, and recently realized that my groups on targets 1 & 3 impact in a different spot than 2 & 4. Basically 1 & 3 group to the right of 2 & 4, or vice versa. Here is one with some Lapua Center X from this morning. Don't mind that low shot on bull 1 lol.

Part of me thinks it's a change in NPA, but I've tried shifting around and it doesn't really change impact. The other part of me thinks that maybe since my front aperture / sight picture overhangs the left edge of the target paper on bulls 1 & 3, and right edge of the target on bulls 2 & 4, that maybe my eyes are tricking me into thinking I'm centered up when really I'm not?

What do you think? It's very repeatable, so whatever it is it's at least consistent.

Edit: on target 3 I actually clicked left 2 after my first shot that landed on the 10 ring line at 230. My first shot on target 4 I still had that 2 left on for shot one which landed on the left side of the x. Then I clicked back over to center and finished the group.

Image


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 Post subject: Re: POI shifting
PostPosted: Sat Jul 08, 2017 2:53 pm 
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Joined: Tue May 07, 2013 8:41 am
Posts: 51
Maybe NPA and/or sight alignment. Overhang on left/right edges of target ? ? What sequence are you shooting the bulls?


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 Post subject: Re: POI shifting
PostPosted: Sat Jul 08, 2017 3:13 pm 
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Joined: Mon Aug 08, 2016 9:58 am
Posts: 18
Yep, it looks like my front aperture is large enough that when centered up say on bull 1 or 3, the left side of the aperture is beyond the left edge of the target paper. Same thing on bull 2 & 4 but on the right side. I zeroed on the right sighting bull at the top of the a23 then shot the bulls in order 1-4.


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 Post subject: Re: POI shifting
PostPosted: Sat Jul 08, 2017 4:41 pm 
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Joined: Tue May 07, 2013 8:41 am
Posts: 51
Sounds like your front aperture is definitely too large. Next question, of course, is what's a good size/line of white around the bull.

This can vary, because some shooters use bloop tubes while others do not. In addition, some like a larger line of white than others; however, too small can cause eye strain. And some like a thin aperture while others like a thick aperture.

Provide your sight radius in inches, and there are plenty of smart guys/gals on here that can make some recommended starting points for aperture size(s).


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 Post subject: Re: POI shifting
PostPosted: Sat Jul 08, 2017 5:45 pm 
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Joined: Sat Jan 23, 2010 8:07 pm
Posts: 128
Location: Washington State
I would check to see if your cant is consistent in prone; I usually have my shooters look at that in prone if they are unsure of why their impact point is changing horizontally. When you shift your NPA left to right, it is very easy for your body to cant a little more to the right, or clockwise to get you on target (meaning that you did not shift enough to the right). At least this has been my experience; I have had a similar problem. A spirit level can help with that; or at least setting your cant indicators. Onw other note however; if you find that this is a consistent problem; maybe click your sights a couple of notches when you shift over. . Not a long term solution but it is worth a shot. Other opinions are appreciated.

-Zach


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 Post subject: Re: POI shifting
PostPosted: Sat Jul 08, 2017 10:56 pm 
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Joined: Mon Aug 08, 2016 9:58 am
Posts: 18
For fun I swapped to an adjustable iris and added a bubble level and my shifting went away. Probably had something to do with the cant. I know I can't use a level in matches but it gives me a starting point to fix it. Thanks everyone.


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 Post subject: Re: POI shifting
PostPosted: Sun Jul 09, 2017 1:21 am 
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Joined: Mon Mar 01, 2004 12:49 pm
Posts: 5216
Location: Ruislip, UK
lee1982 wrote:
For fun I swapped to an adjustable iris and added a bubble level and my shifting went away. Probably had something to do with the cant. I know I can't use a level in matches but it gives me a starting point to fix it.

Which rules are you shooting under that don't allow a spirit level for smallbore rifle?

ISSF rules only prohibit them for 300m Standard Rifles and 10m Air Rifles (7.4.2.2 & 7.7.5).


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 Post subject: Re: POI shifting
PostPosted: Sun Jul 09, 2017 1:50 am 
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Joined: Sun Sep 04, 2016 10:59 am
Posts: 469
Location: A new global Great Britain
Anschutz wrote:
Provide your sight radius in inches, and there are plenty of smart guys/gals on here that can make some recommended starting points for aperture size(s).

http://www.hamptonrifleclub.org.uk/cons ... m#Formulae

may help.


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 Post subject: Re: POI shifting
PostPosted: Sun Jul 09, 2017 10:32 am 
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Joined: Mon Aug 08, 2016 9:58 am
Posts: 18
Thanks. I didn't realize levels were allowed.


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