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Apr 29th, 2024
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Joined: Dec 2006
Posts: 629 Likes: 1
Sidelock
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OP
Sidelock
Joined: Dec 2006
Posts: 629 Likes: 1 |
If one would want to move the POI a few inches in one direction is there any way one can calculate how many thousandths of an inch to remove from the choke from that side? Something like the formula used for stock bending where if the POI is 1 inch from POA, then one bends the stock with 1/16th" for a 16 yards target.
I have some ideas in mind depending on the constriction one starts with and the POI at a certain distance to calculate the new choke constriction so that the new POI brings the POA in the center...
Of course, moving the pattern in one direction will imply widening of the pattern.
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Joined: Mar 2002
Posts: 7,733 Likes: 492
Sidelock
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Sidelock
Joined: Mar 2002
Posts: 7,733 Likes: 492 |
Eccentric choking does not always result in a change of impact on a one for one basis. I have seen one eccentric choke that just made the pattern very poor on one side. Did not move the entire pattern towards the left as expected. Might be better to leave as is unless you have POI divergence which is a foot or more difference. Slower or faster loads will sometimes change the POI as well.
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Joined: Jan 2002
Posts: 5,983
Sidelock
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Sidelock
Joined: Jan 2002
Posts: 5,983 |
I have adjusted the POI on cheap Brazilian .410s with a 3/8" rattail file. Cut and test. The impact will move over just like moving the front sight. Want to go right, remove a little steel from the inside right of the muzzle. Polish it when you're happy. Of course the pattern will widen slightly but that beats the heck out of missing the target, with all of the shot.
> Jim Legg <
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Joined: Feb 2006
Posts: 1,600 Likes: 13
Sidelock
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Sidelock
Joined: Feb 2006
Posts: 1,600 Likes: 13 |
Have you tried a number of different loads or ammo manufacturers to determine if the POI you are experiencing is consistent through all possible ammo combinations?
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Joined: Dec 2006
Posts: 629 Likes: 1
Sidelock
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OP
Sidelock
Joined: Dec 2006
Posts: 629 Likes: 1 |
I changed the POI on an old Darne that came with XF/XF chokes. I wish I had taken notes at that time because I moved the POI where I wanted it and opened the chokes to IC/M.
I think one can calculate how much to remove from what side of the barrel by measuring the diameter of the final theoretical pattern so that the POA coincides with the POI and figuring out the constriction difference in thousanths and removing that much from where need be. Something like that.
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Joined: Nov 2002
Posts: 937
Sidelock
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Sidelock
Joined: Nov 2002
Posts: 937 |
Twice I have had problems with crooked chokes shooting off POA.
In one case, some aggressive "polishing" of choke, making it more concentric, helped a lot. However, still needed to find load(s) that did give centered patterns. Was successful, with at least a small number of loads.
On one barrel of a cheap Spanish double, pattern was both very irregular and off center. Finally found a single load that gave nice even and tight (80+%) patterns from that barrel, as well as 70+% patterns from other barrel. Used that load happily with that gun for many years.
Niklas
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