Rifle sight-in *Help Needed*


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Bane
November 9, 2006, 10:36 AM
I am in a tough spot due to poor planning. I need to sight in my rifle for deer hunting tomorrow and I only have access to a 25yd range. My questions to you all are: How high do I need to sight in at 25yds to be zeroed at 100yds? Where will this put me at 200yds?
(In all likely hood any shot I take will be at less than 50yds but I still would like to know roughly were I am at distance.)

I am shooting a rifle in 308 Winchester with a 22" barrel with 1 in 10 twist. I will be using 150gr Winchester Super X.

All input would be greatly appreciated.

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rezman
November 9, 2006, 10:58 AM
Assuming scope centerline is 1.5" above bore, 25 yard zero is very close to 200 yd zero, probably 2-2.5 inches high at 100. Of course it helps greatly to verify at the actual range you intend to shoot at.

HTH.

Bwana John
November 9, 2006, 11:18 AM
Its a funny thing....

Almost ALL calibers will be right on at the correct range if first zeroed @ ~25m.

ie- .22lr; zero @ 25 m, 3/4" high @ 50m, zero again @ 75m---perfect!

30-30: zero @ 25, 1.5" high @ 100m, zero again @ 150--- again perfect for the caliber

308: zero @ 25m, 2" high @ 100. zero again @ 200 m

7mm mag: zero @ 25m, 2.5" high @ 100, zero again @ 230 m.

No matter what the power of the cartridge, a 25 m zero usually works pretty well. A scope mounted really high will mess this up a little, but overall this has worked OK for me.

I would get out and see where the rifle is actually printing, any errors in sighting in will be 8 times larger @ 200m.

Froggy
November 9, 2006, 11:55 AM
Assuming scope centerline is 1.5" above bore, 25 yard zero is very close to 200 yd zero, probably 2-2.5 inches high at 100. Of course it helps greatly to verify at the actual range you intend to shoot at.

Mensch! I'm impressed rezman. Pretty darn close to what my ballistics calculator gave (and I'm assuming you did that in your head?).


Bane, here (http://www.winchester.com/products/catalog/cfrdetail.aspx?symbol=X3085&cart=MzA4IFdpbmNoZXN0ZXI=) is the link to Winchester's data for that round. Unfortunately, it does not include a 25 yard entry. But you can take the MV and ballistic coefficient off their chart and plug it into this gizmo (http://www.norma.cc/htm_files/javapagee.htm) to get the numbers you want.

Over on the left side of the page, click on "define your own bullet" and pump in the bullet weight and coefficient. Then use your mouse to:

- move the range marker (the long red line) to the 25 yard mark

- adjust the MV to 2820 fps

- adjust the "height of sight line" to the distance from your bore to the center of your scope

- set the "zero range" to your desired setting (probably 100 or 125 yards).

Now look at the box near the top right to read "H of traj ichs"... that is the desired height of the bullet above / below the "X" on your target at 25 yards to get it zeroed at your chosen range. In this case, it looks like you want the bullet about 0.7" low at 25 yards to be zeroed at 100 - 125 yards.

Move the range marker (the long red line) over to the 200 yard mark to see where the bullet is relative to your zero point at 100 yards. In this case, it looks like it will be about 3.4" low at 200 yards.

Playing around with this thing and watching the window of "point blank range" (bullet +/- 3" from LOS) you might decide to zero for 200 - 225 yards. To do that at 25 yards for 200 yards, you want your POI about 0.2" below POA; that will have the bullet 2" high at 100 yards and zeroed at 200 yards. Getting the bullet right on the "X" at 25 yards should have you zeroed for 225 yards and about 2.8" high at 100 yards.

Of course, as rezman says, you'll want to double check on a measured range.

Bane
November 9, 2006, 01:59 PM
Great info everyone. Thanks very much. I think I will go for the 200yd zero. Hopefully, I will get to sight-in at 25yds and shot out to 100yds to verify before my hunt. Thanks again for the help.

bclark1
November 9, 2006, 07:13 PM
Hopefully this isn't a new gun and you've done a fair bit of shooting with it on more than the 25? I've had the rifle I'll be using next week for two years now. It must've taken a bump because the scope was well off when I brought it to the range to check it. I got it re-zeroed, but I'm still killing myself driving an hour and a half to the nearest long range to do as much shooting as possible before the season. Just had to order another $100 of ammo because I'm down to half a box of my hunting rounds. I really don't have the time or money for it right now but I'm just trying to impress that you should really have all the guesswork out of your shooting by the time you're pulling the trigger on a live animal. I apologize for being on a soapbox but I just felt it'd be good to put out there, even if only for people who might come across this thread in the future.

One of Many
November 9, 2006, 07:42 PM
It is very important to sight in with the same ammo you will hunt with; that means ammo from the same lot number, as well as same manufacturer and style/weight. I buy my hunting ammo in multiple box units, with the same lot number, so I have enough ammo to adjust the scope, and more left for the hunt(s).

Some people do not realize that there can be a significant difference in the shooting qualities of different lot numbers of the same ammo. Most people know that different style/weigh bullets, and brands, will cause a shift in point of impact. My experience is that shifts in POI due to changes in ammo will be lateral (sideways) as well a elevation (hidh/low).

There are free balistic programs from at least two ammo companies, that will show the expected average path for a particular load made by that company. These are good guides for setting up the scope so that you have a Point Blank Range (+/- 3 inches of point of aim) out to maximum hunting range. Most scope mounted centerfire rifles will shoot low at 25 yards, near POI at 50 yards, and 2 to 3 inches high at 100, when sighted for maximum Point Blank Range. This gives you the elevation info you will need to maximize your rifle's usable range..

Bane
November 9, 2006, 09:38 PM
Thanks for the concern guys. The rifle is fairly new. I purchased it about 6 months ago to use for hunting. However, I don't need hundreds of rounds and a few years to learn where my rifles shoot. I had put a few boxes of ammo through the rifle before today without any issues. My only concern was sighting in with the new ammo I purchased to hunt with. I bought a few boxes from the same lot to sight/hunt with. My main issue was not being able to sight in at long distance. Fortunately, this afternoon I was able to shoot at both 50 and 100yds. I found that if I was 2 inches high at 100yds I was almost dead on at 50yds. This gives me plenty insight as to where to aim to make a humane kill when hunting. Thanks again to everyone who offered insight.

rangerruck
November 9, 2006, 09:59 PM
I have found that if you zero a midrange centerfire at 25 yds, with it being deadzero to a hair below, this puts you good for a zero at to a little beyond the 200 yds range, with still being a good kill dead on hold, out to 275yds, with a deer sized animal.

redbone
November 14, 2006, 12:16 PM
If you are unable to shoot at anything longer than 25 yards before the trip, I'd strongly suggest that you pass up any shots over 50 yds while hunting.

Good luck!

RBH

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