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Joined: Dec 2001
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Brian Offline OP
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Got to thinking about zeroing double rifles with scopes. A good one should be able to maintain 200 yard deer killing accuracy; 4-5" groups at 200 yards for the first two shots out of the gun (one pair) fired cold.

so, with that in mind, here are a few questions:
1. if the gun shoots a 4 shot group at 100 yards 2 1/2", and each barrel puts its two in touching or almost touching clusters, would you make the right barrel the point of aim point of impact zero and know that the left barrel is 2 1/2" left or would you center the group where neither [air is exactly on point of aim but each is 1 1/4" off to either side?

with the pairs either side of center, then when shooting at 200 yards, you find that the group grows to 5" and favors to the left of center by 4 inches. No crossing is evident.

or would you zero with the right barrel at point of aim at 100 and see where it shoots at 200 and then after its centered at 200 yards check the left barrel to see where it is.
It is more about the first shot being the most precise. In woods hunting, you often have to slip a bullet between the trees with little margin of lateral error.

I will be doing some tests myself with this theory in the spring with my 7x57R.
More to follow then

your opinions are appreciated

Last edited by Brian; 12/30/14 08:43 PM.

Brian
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Might try tweaking the load/bullet weight, to bring the groups closer together. Faster loads print closer together, assuming the rt barrel shoots to the right. If it crosses, a slower load will bring the shots together. Also depends on how tightly the gun is held--you have to hold it like you would when hunting, as in not shooting off a rest directly, but just an arm rest, and standing, so the gun recoils as it would when hunting.

Last edited by xs hedspace; 01/01/15 01:53 PM.

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PS: A change of .2 grains of powder can make a difference. If you see a .002-004 case stretch after firing, and the chamber/headspace is tight, that can be an indication that max load is achieved. Had to drop the charge in my .45-100, when I saw the stretch marks at the case web after 4 reloads.

Last edited by xs hedspace; 01/02/15 03:51 PM.

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XS, Can you tell us the load you were using in your .45-100 when you started to notice the case stretching? Thanks,Bob

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Well, my box of regulated(1.5" at 50yds) has a note saying 75.5 gr 4064, with a 350 gr hornady RN, so it probably was 76 gr. Getting old, CRS syndrome, but I keep notes. WW mag primer.


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If you get traditional pressure signs(expansion,etc)in doubles,drillings,etc;you are way "over pressure" for the good of the gun.
Mike

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As I remember, the cases would stretch about .005" at 76 gr, so I dropped it to 75.5, and the stretch went down to .002". BTW, I throated this DR long, so I could seat these 350 gr out to the second cannelure, to keep pressure down. Regulation is good enough for minute-of-boar--too bad about the 3" hole in the slab of bacon from the far side---bang, flop, done.


hippie redneck geezer

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