zeroing a 308/


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Victor1Echo
January 18, 2010, 12:12 PM
I am in the process of zeroing in my rem 700 sps in 308 20" barrel. I know that the 308 has an arcing trajectory, and in the Gun Digest ballastics they start at the 200 zero. Is the 200 yard range a better/ more accurate range to zero a .308?

Thanks

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Ridgerunner665
January 18, 2010, 12:19 PM
A 200 yard zero works well with the 308...it will be approximately 2 inches high at 100 yards, depending on bullet weight and muzzle velocity.

Art Eatman
January 18, 2010, 01:46 PM
For most hunting use, zeroing at 200 yards is pretty much a "set it and forget it" deal. Most game animals are taken inside of 200 yards. With that zero, the bullet drop at 300 yards is only about six inches, so not much holdover is needed for the relatively few shots to be taken at that distance.

For shooting at paper, there are two choices. If it's a hunting rifle and the purpose is to test a load, only the group size is important, not whether or not you center the bullseye. After testing, you merely adjust the scope to put the group at your desired point of aim, as necessary

If you are actually trying to hit the center of the bullseye, you merely adjust your scope for zero at that particular distance.

lomfs24
January 18, 2010, 01:52 PM
I personally have my .308 set up to punch paper out to 1000 yrds. So I have a 300 yrd zero and have my rings set so that I am close to the bottom of my scope travel at 300 yrd zero. That way it gives me all the adjustment I need to get out to 1000. This makes it 4.5 inches high (give or take depending on the load) at 100.

I am not saying that is right or wrong, it's just how I do it.

Victor1Echo
January 18, 2010, 06:56 PM
Is a hundred yard zero just as good? Does it matter?

James T Thomas
January 18, 2010, 07:13 PM
The "battle sight zero," with the M-14 was at 250 meters: 273 yards.

That would produce a 2 3/4 inch high impact at 100 meters.

With commercial rifles and ammunition, I think the variation would be minor from that.

kanook
January 18, 2010, 07:16 PM
Mine is set at 150yds. The longest shot might be 250yds but my usual shot is around 50-120yds. My impact is a little high for my close in shots and a little low for my distant shots. My barrel is 16"

dubbleA
January 18, 2010, 07:25 PM
Pretty much a personal preference on zeroing a firearm.What works for one might not for another. Personally I like a 100 yard zero and will get to know the ballistics of the cartidge I am using by actually shooting at the ranges I intend to shoot and recording the dope.

Uncle Mike
January 18, 2010, 07:37 PM
I'll have to agree with dubbleA on this one...if your not doing anything spectacular with the rifle, such as really long distance communication, then the 100y zero is perfect for the .308.

It allows pretty easy memorization of trajectory past zero range...everything on your side of the zero range is fairly mute as to trajectory.

Fred Fuller
January 18, 2010, 07:47 PM
Victor,

The thing to keep in mind is that your bullet crosses your line of sight twice- once as it rises through the line of sight fairly close to the muzzle, at 25-30 yards or so depending on caliber and zero, and again as it descends through the line of sight in its parabolic plunge back to earth. Usually the second point at which the bullet crosses the line of sight is what most people think of as that rifle's zero.

We're really dealing with three "lines" here- two of them perfectly straight, and the third curved- the third line being the trajectory of the bullet, which is a parabola. The first line (one of the straight ones) is the line of the bore, which extends to infinity from the rifle's muzzle in the line created by the bore itself. The second straight line is the line of sight, which also extends to infinity and is the line created by the rifle's sights.

The two straight lines (line of sight and line of bore) intersect at only one point- they're straight lines extending to infinity, remember? On a conventional rifle, the sights are placed above the bore, and in order to hit anything, the rifle has to be sighted in. That means that the line of sight is depressed to the point where it intersects the line of the bore (or the line of the bore is elevated until it intersects the line of sight-whichever).

That means that when the bullet is launched from the muzzle, it is angled upward by the line of the bore to cross the line of sight. Since bullets travel in parabolas and not straight lines, however, that means it crosses the line of sight TWICE- once as it rises, the second time as it descends.

Maybe reading http://www.chuckhawks.com/bullet_trajectory.htm will help explain this better.

If you're shooting at tiny targets at exactly 100 yards, a precise 100 yard zero matters. My neighbor's kids used to like to shoot my .223 bolt gun with its fixed 6X scope, and their favorite trick was to shoot (from a bench rest) through the cap of a 2-liter bottle full of water laid on its side at the 100 yard line. For their sakes I kept this particular rifle zeroed at exactly 100 yards. The results of a precise hit weren't much different from a miss of an inch or two, but finding the cap with a .22" hole in it gave them a real charge.

Zero depends mostly on the purpose of the rifle. If you're shooting at deer or other large game at typical hunting ranges, you're handicapping yourself unnecessarily most of the time to zero precisely at one hundred yards. The exception (and there's always at least one exception) is if you're using a scope with a reticle precisely calibrated to your caliber and load, with stadia lines or other markings for various ranges.

In the case of the typical hunting rifle, it's usual to zero about 2.5" high at 100 yards. That maximizes the distance at which your rifle will be "minute of deer" without having to hold over. See http://www.rockymountainhunting.com/articles/articles-scope-sighting.html for more a more detailed explanation.

And for more, see http://www.chuckhawks.com/rifle_trajectory_table.htm .

My current project is a new Savage 93R in .17HMR. It's outfitted with a Sightron II 4-16x42 scope. After looking long and hard at the drop tables at http://www.varmintal.com/17hmr.htm , I decided to zero it at 1.5" high at 100 yards. That puts it dead on at 165 yards, which is a pretty good haul for a pipsqueak rimfire round. But it means the bullet is never more than 1.5" above line of sight out to that magic 165 yards, and it ought to be no more than 1.5" low out as far as almost 200 yards. Since this is a varmint caliber suited for small varmints, that means out to about 200 yards or so I shouldn't have to worry much about holding over. That's not too shabby for a little bitty rifle shooting little bitty (17 grain) bullets. I haven't had access to a 200 yard range to confirm that yet, but I will...

hth,

lpl

dubbleA
January 18, 2010, 07:51 PM
It allows pretty easy memorization of trajectory past zero range...everything on your side of the zero range is fairly mute as to trajectory.


This is a very good point.

This doesnt apply for the 308 Win but in some cases in high velocity cartridges having a to much of an offset, say 3 inches high at a 100 yards can get into trouble hitting small targets at mid ranges as the bullet is still rising.

sig220mw
January 18, 2010, 09:05 PM
I have my 308 sighted in at the "battle sight zero" per James' post. Didn't know it had a name though. But I agree with dubbleA . The 100 yd sight in works well and after the sight in you shoot at 150, 200, 250 and 300 yards and make note of what the bullet does at the various ranges.



unclemike it's moot not mute

Uncle Mike
January 18, 2010, 09:12 PM
Hey Victor...check this out.
http://www.norma.cc/default.asp?Lang=2

Right upper corner, click 'ballistics' US and play with the calculator, it gives you a visual path of your bullet at varying zero settings.

You'll be able to see your close zero(the point were the bullet crosses the line of sight for the first time), and your far zero, the zero you set and use, (this is the point were the bullet crosses the line of sight for the second, and final time).

DMK
January 18, 2010, 09:45 PM
Is a hundred yard zero just as good? Does it matter?

Regardless of what anyone else tells you they zero their rifle at, you need to ask yourself two questions:

1) What is the distance you need to shoot at?

2) How close to your point of aim do you need to be?

The shorter the distance, the closer you will be to your point of aim without changing your zero (assuming a perfect shot).

With a 200y zero the rifle can shoot a group centering somewhere within 2.5" or so (in elevation) to where you aimed, at anywhere between you and 250y. At 300y, you'll be about 7" low.

With a 100y zero your group center can be within 1.5" of aim but only out to 150y, after that it drops to about 3-4" low at 200y, then 5.5" low at 225y and about 13" low at 300y.

Uncle Mike
January 18, 2010, 10:26 PM
unclemike it's moot not mute

Yes it is...many thanks. Everybody's in a big hurry! lol hehehehe

mshootnit
January 18, 2010, 10:31 PM
Yeah, I'd go 250, but I am used to open country.

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