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 Post subject: POI jumps north
PostPosted: Sat Jan 07, 2017 10:12 am 
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Joined: Fri Oct 04, 2013 9:06 am
Posts: 72
Location: Surrey
I'm pulling my hair out with this one, so any advice would be greatly appreciated.

Shooting a UK 10 bull 25yd target, after good sighters move on to the target. Suddenly POI jumps into the nine ring at 12 or 1 oclock, this could be the first or anywhere upto the 4th shot (at this point my only body movement has been right to left with no elevation change). I drop a point or two before sight adjustment is correct again. Continue around the card and whatever shift in position had happened is undone so now shots suddenly drop back into the nine ring at 6 oclock. These are big jumps, like taking the spot all the way to '**** that was nearly an 8'!

I'm looking through the centre of the rear sight and checking my NPA on every shot. What other possible causes could be causing this?

many thanks
Bryan


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 Post subject: Re: POI jumps north
PostPosted: Sat Jan 07, 2017 12:41 pm 
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Joined: Sat Feb 05, 2011 8:55 am
Posts: 11
Location: Canada
My best guess is NPA not good enought. It is the no1 mistake when shooting at closs range on multi bull target.

After that, up and down impact shift could also be related to tension changes, sling vs cheekpiece, vs butt plate.

All the best, Mart


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 Post subject: Re: POI jumps north
PostPosted: Sun Jan 08, 2017 9:27 am 
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Joined: Wed Jan 25, 2012 6:10 pm
Posts: 79
Not sure if you are shooting prone or standing. Either way, relaxation of the right shoulder (right handed shooter) is critical. Important for all positions but more so for prone.


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 Post subject: Re: POI jumps north
PostPosted: Mon Jan 09, 2017 12:28 am 
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Joined: Mon Jan 24, 2011 7:17 pm
Posts: 21
A few question, How many sighting shot you made before move onto record?

How old is the barrel? How often do you clean the barrel?

Did the shifting POI usually happen after certain number of shots? and the POI change back to normal after you made a sight adjustment and fired a number of shots?

Assuming your technique is correct, my guess the problem is your barrel, either its not clean when start shooting or its wore out.

Check your barrel, especially the area just in front of the chamber.


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 Post subject: Re: POI jumps north
PostPosted: Mon Jan 09, 2017 5:08 am 
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Joined: Mon Jan 03, 2011 11:33 am
Posts: 1130
Location: Taunton, Somerset
Bryan,

Do you see the same thing if you just fire on the sighter? If no, that would suggest under/over-cleaning is not the issue.

Any recent changes to the butt or sling? Do the high/low shots look different in the recoil?

You did mention previously that you thought your then batch-tested Midas was not quite such a good match now the barrel had broken in, could the new tuner be exaggerating this?


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 Post subject: Re: POI jumps north
PostPosted: Mon Jan 09, 2017 6:47 am 
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Joined: Fri Oct 04, 2013 9:06 am
Posts: 72
Location: Surrey
Thanks for all the reply's.

Sallar600 - it might just be a poor NPA, although I've not really had this problem with it before.

Bugman - This is prone. Wouldn't a tense shoulder push shots low into 7 and 8 oclock?

Tony C - New Trueflite barrel, only 1 year and 4000 rds old. I clean everytime I use it both before and after. I normally shot about 3 sighters before moving onto the card. Yes the POI is returning to the original after shooting a few more rounds.

Tim S - I'm currently using centre X, Midas and some Eley Tenex Pistol (I have reason to believe that round nose bullets work better in my very shallow leade but this isnt proven yet!) You may be right with the buttplate, I spent last night dry firing at home and adjusting it slightly. I've booked thursday off work and will spend all day at the range trying to sort this out. I'll try shooting groups first and see what happens without moving. I dont have any reason to suspect the tuner could cause a shift. I actually did some testing a few weeks ago with the tuner at 50m off a rest and it does definitely work.

I have this feeling its maybe got something to do with butt plate and shoulder, sling tension, support arm or cheek pressure.

thanks


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 Post subject: Re: POI jumps north
PostPosted: Mon Jan 09, 2017 8:01 am 
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Joined: Sat Aug 01, 2009 12:09 pm
Posts: 61
Location: Charleston, S.C.
Bench the rifle in a rest and see if it happens then. Test it with both types of ammo to see if the results match. If you still get the shift are you certain that there is no source of vibrations from something loose on the gun? Barrel is floated and not making contact? Actions screws properly tightened? Bedding is OK? Barrel screwed, glued, clamped, or pinned? If clamped is it set properly? Did this start with the addition of the tuner?


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 Post subject: Re: POI jumps north
PostPosted: Mon Jan 09, 2017 12:57 pm 
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Joined: Mon Jan 24, 2011 7:17 pm
Posts: 21
Other poster have gave you a number of good suggestions, however I still think the cause of shifting POI is your barrel, you may have one of those barrel when its cold and clean, need more than a few shots to settle down, you can try to bench rest it and see when the shift occur and how many shots later settle back to normal, back when I'm shooting smallbore I have a 1913 that shot very well but will need about 15 fouling shots for it to shoot consistently, different type of ammo didn't make any difference,.

Barrel making is a bit of black art, if your barrel shoot well, I'll live with it, going to cost a bit more for your ammo though.

Best of luck, please let us know how it turns out after your next range session.


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 Post subject: Re: POI jumps north
PostPosted: Tue Jan 10, 2017 4:59 am 
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Joined: Mon Jun 25, 2007 5:06 pm
Posts: 336
Location: UK
How are you moving around the target? Where is your sighter?

Conventional wisdom has the sighter to the left of the target and people then start top left and work clockwise across the top row, down the right hand side, and leftwards back along the bottom row finishing on the left-middle bull.

Assuming this is how you shoot (and if not, let us know what your order of shooting is), then I'd suggest your orientation/NPA is not good enough and that when you shuffle your position to move left-to-right from the sighter to the bull you are actually shuffling backwards a little bit or allowing your right shoulder to come back. A loose fit in the shoulder will then cause elevation error from recoil, etc. The fact you are then getting low shots later on (when you are moving right-left along the bottom row?) likewise suggests some sort of erroneous forward/downwards movement whilst you are shuffling left.

Lots of people have proposed that your barrel is problematic or that it needs more sighters to "warm up" than you are giving it. There is a simple way to test this - shoot groups. Fire shots on the same bull without touching the sights and see if the point of impact moves from the initial group upwards and when it does so (after 2/5/10/15 shots?). If you have a nice round group after 20 shots or a couple of loose shots followed by a round group, then it's not the barrel changing and most likely it's you not moving properly.


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 Post subject: Re: POI jumps north
PostPosted: Tue Jan 17, 2017 5:05 am 
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Joined: Fri Oct 04, 2013 9:06 am
Posts: 72
Location: Surrey
Finally got to the bottom of this. Butt plate was slipping, either whilst reloading or under recoil. I've tilted the the butt plate back slightly to get more purchase and that's solved the issue.

Thanks for everyone's input.


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