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Re: Bullets Different Point of Impact [Re: country_20boy] #15674196 01/18/21
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dan_oz Offline
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Originally Posted by country_20boy
Follow up question.

If POI for different bullet weights and types is several inches apart left and right, what can be deducted from this?


The rifle starts to recoil as the bullet starts to move, and so POI is affected by, among other things, how much recoil and how much time between the bullet starting to move and it leaving the muzzle. Just to complicate things, the rifle doesn't recoil straight back, but tends to pivot up at the muzzle (because the recoil is transferred via the butt, below the line of the bore on most rifles). It can also pivot laterally due to things like cast and the effect of the shooter's cheek and other aspects of how the rifle's held. In fact it is for this reason that you can get different POI from different shooting positions, even without changing loads.

As well, with all of this movement the barrel is not infinitely stiff, and it tends to flex as all of this is going on, and this in turn can be affected by contact with the fore-end.

All of these things can contribute to different POI, including lateral shift.

Usually all of this doesn't matter all that much: you zero for the load you'll use, and (if you're smart) from the position you'll favour for the longer shots, and leave it at that. It only really starts to show up if you are shooting different loads, positional matches, or trying to regulate a double rifle.


BP-B2

Re: Bullets Different Point of Impact [Re: keith_dunlap] #15677929 01/19/21
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reivertom Offline
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All of the above or none of the above. You just have to shoot them to find out.

Re: Bullets Different Point of Impact [Re: Windfall] #15677986 01/19/21
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Boise Offline
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Originally Posted by Windfall
Biggest difference that I ever saw was helping a guy sight in a Browning BAR during our annual sight in days. Without touching a thing and only changing brands of ammunition and maybe the bullet weight, his .30-06 was grouping into the next target over.


Had a similar experience but then saw I had one 4 shot group and one 6 shot group, wasn't an equipment problem.


The difference between genius and stupidity is that genius has its limits. Albert Einstein
Re: Bullets Different Point of Impact [Re: keith_dunlap] #15678915 01/19/21
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navlav8r Offline
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I feel lucky if different weight bullets DO impact close together. I have a 35 Whelen that puts 225 Accubonds about 1/2” higher that the 200 Accubond that’s a bit higher velocity. That puts them pretty close together down range.


NRA Life,Endowment,Patron or Benefactor since '72.
Re: Bullets Different Point of Impact [Re: navlav8r] #15679017 01/19/21
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Mule Deer Offline
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Originally Posted by navlav8r
I feel lucky if different weight bullets DO impact close together. I have a 35 Whelen that puts 225 Accubonds about 1/2” higher that the 200 Accubond that’s a bit higher velocity. That puts them pretty close together down range.


What powder(s) are you using?

One thing I've found during my experiments at very different temperatures is that POI can vary considerably with temp-sensitive powders.

An example from 20+ years ago was working up two loads for my .338 Winchester Magnum, one with 200-grain bullets and RL-15, and another with 250s and H4831 Extreme. They shot close to the same place at 70 degrees Fahrenheit, but not at 90 degrees in Africa--or at around zero F. in Montana.


“Montana seems to me to be what a small boy would think Texas is like from hearing Texans.”
John Steinbeck
IC-A

Re: Bullets Different Point of Impact [Re: keith_dunlap] #15680559 01/20/21
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cra1948 Offline
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I have an extremely accurate, custom, heavy-barrel AR in .223. It shoots bugholes with 60 grain Sierra HP’s over Varget. It also shoots bugholes with 65 grain SGK’s over Varget. The 65 grain bugholes are 3/4” from the 60 grain bugholes at 2 o’clock.



Mathew 22: 37-39

Happy escapee from NY

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