.308 sight in....how to?


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skipbo32
September 16, 2010, 10:56 AM
if i want to sight in my .308 at 200 yds, cant i sight it in at 50yds? what short distance can i use to get my zero at 200yds.....thanks.

my gun is a M1A that shoots a 150 grain bullet

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Olympus
September 16, 2010, 11:05 AM
Google "how to sight in a rifle". Different people use different approaches.

In theory you can sight your rifle in at 50 yards and use a bullet drop table to calculate what the drop would be at 200 yards. Get it sighted in at 50 yards and then raise your POI approximately what the table says the drop would be at 200 yards. Not a method I would personally use unless I could actually get some shots out to 200 yards to double check. And if that were the case, just zero it at 200 yards to begin with.

jmorris
September 16, 2010, 11:10 AM
You need more information to be exact but if you were using a 150 fmj with a ballistic coefficient of .398, traveling at 2800 fps and a sight height of 1.5” you would be at zero at 30 yards and again at 200 yards.

If you only have 25 yards to work with you would need to be .2” low.

jmorris
September 16, 2010, 11:11 AM
If you have more data you can go here and plug it in yourself.

http://www.jbmballistics.com/cgi-bin/jbmtraj-5.1.cgi

heeler
September 16, 2010, 11:21 AM
In all honesty you really need to sight it in at two hundred yards because if you are trying to use some ammo makers ballistic tables to attain these results at 25 or 50 yards one has to understand that they generally use a 24 inch barrel to achieve these results and near perfect conditions as well to make their ammo look so great vs their competiters.
The mounting heighth of your scope also plays into account.
Then that particular ammo in that particular weight grain just might not do as well in your particular barrel.
I learned a long time ago about this using a .270 sighting it in at 25 yards thinking it would be dead on at 200.
I was wrong.
Not sure if your just target shooting or going deer hunting here.
On both of my 308's that I use for deer hunting I sight them in to shoot two inches high at 100 yards.
My Remington 600 with it's 18.5 inch barrel in 308 is still about an inch and a quarter or slightly a little more low at 200 yards but my model 700 with it's 22 inch barrel is just about spot on.
This using Federal blue box 150 grain ammo which both my rifles simply love.
Lastly,most hunters,although not always true, dont shoot much past 100-125 yards at deer,if even that far.
So I have seen a number of guys over the years that sight in at 100 yards and practice predominately at these ranges do some terrible shooting when a true 200 yard target or farther distance target appears.
200 yards can be a very long shot for the unfamiliar shooter.

DPris
September 16, 2010, 11:57 AM
Trajectory tables are nice for coming close, but there are enough variables involved that the ONLY way to sight your gun in at the distance you want to shoot it is to sight it in at the distance you want to shoot it with the load you want to shoot in it at that distance.
Period.

The tables are generic, don't take into account barrel length, stock types, scope heights, shooter variations, bullet variations, type of rifle rest (or method of sighting in), elevation, humidity, and so on.

Likewise zeroing at 25 or 50 yards will only put you close.

If you want to sight it in for 100 yards & then have the ability to take a longer shot at 200 yards, sight it in at 100 & fire enough at 200 so you know what holdover (if any) you'll need. I sight most of my centerfire rifles 2 inches high at 100 & that carries into point blank aiming out to 200.

Last time I did a beginning zero with a .308 at 25 yards just to get on paper with that gun & scope, when I took it to the range it was high & right at 100 yards for final zeroing.

There is no accurate substitute for zeroing at longer ranges, if you want best accuracy.

Denis

skipbo32
September 17, 2010, 01:29 AM
thanks guys,

i noticed two of you sight your gun in 2" high at 100yds to hit dead on at 200yds. i have always sighted in 1" high at 100yds because i thought the bullet drop from 100-200yds was only 1".

lloveless
September 17, 2010, 01:53 AM
I always sight in 3 inches high at 100 yds. with my .308 and 150grs a la Jack O'Connor.
ll.

Ragnar Danneskjold
September 17, 2010, 02:03 AM
Might I ask what the purpose of this rifle is? You may consider building your own ballistic table for specific ranges with a certain load, so that you can do quick adjustments on the fly if your range changes.

DPris
September 17, 2010, 02:54 AM
In my case, I'd have to define "dead on". :)

My definition of point blank zeroing is setting up the rifle, sights, and load so that using the same sight picture and point of aim (or aiming point) will put a bullet either into a deer-sized animal or a human sized threat at 100 yards on out to 200 yards.

Dead on, to me, means putting the bullet exactly to point of aim (i.e. aiming at the exact spot you want to hit & having the bullet land exactly there). I don't do "dead on". :)

This may sound confusing.

Most of my flatter-shooting rifles from .223 on up to .30-06 (excluding the rainbows like the .45-70) are zeroed to strike two inches above my aiming point at 100 yards as a known standard, since that's a more commonly used distance where I'd be more likely to take a shot.
I can use the same sight picture & point of aim (aiming spot on the target) at 200 yards as I do at 100 yards, without holding over or guesstimating & adjusting point of aim, with the expectation of striking close enough inside those two target sizes to be effective, but not with the expectation of striking exactly on the spot I'm aiming at.

In other words, if I were to aim pretty much dead center elevationwise behind the shoulder of a good-sized deer at 100 yards, I'd be no more than two inches above the spot I was actually aiming at & still drop the deer. Aiming at exactly the same spot on the same-sized deer at 200 yards will not put the bullet in either the same exact spot as it did at 100 yards, or exactly at the spot I'm aiming at.
The bullet will obviously drop farther at 200 yards than it did at 100, but if I have a decently flat-shooting caliber & bullet, bullet drop will (if I do my part) be minor enough to still strike the vital area in the torso behind the shoulder and drop the deer.

I can use the same aiming point at 100 and 200 yards with no holdover or guesswork, and the bullet should strike close enough to the aiming point at 200 to be effective.
So, I don't consider a two-inch-high 100-yard zero to put me "dead on" at 200 relative to the bullet striking right where the sights are pointing, just "on" enough to put the front sight in the same place on a reasonably sized target anywhere from 75 yards out to at least 200 and hit the target.

Using a 12-inch plate as a visual aid, if I have my rifle zeroed for two inches above point of aim at 100 yards, the bullet should strike two inches above center if I aim dead center. I won't hit where I'm aiming, but I'll break the plate.
Aiming dead center at 200 yards, the bullet may drop 2-4 inches (depending on caliber & load) and strike two or three inches below dead center. I don't hit the precise spot I was aiming at, but I still break the plate.

This obviously varies with gun & load, but illustrates the point.
A flatter shooting caliber with less bullet drop out to 300 yards is more important in varmint hunting, but not so much in most big game hunting applications. 300-yard shots are outside the norm. If you want to take your rifle out that far, you'll need to shoot it at 100, 200, and 300 yards & learn how much bullet drop you get beyond your basic 100-yard zero.
Some people do zero three inches high at 100, depends on what they know their gun can do & what they want it do do.
Matter of individual choice & requirements.

This point blank range is not limited to 200 yards, by the way, I just use 200 as an example.
Some calibers shoot flat enough to maintain a point blank zero substantially farther out.
Rifles like the .45-70, on the other hand, can require a lot of holdover beyond 150 yards.

Again- the ONLY way to tell for sure what your gun & load will do at 100, 200, and beyond is to shoot it at those distances. Everything else is by guess & by golly. :)

Denis

skipbo32
September 17, 2010, 03:23 AM
thanks denis,

i am using this gun to hunt with. i just need to get out to the range to zero it. my gut says zero it at 200yds because the .308 levels out around that distance. that way if i am shooting anywhere between 100 and 300yds i should have a six inch margin of error (up or down).

http://i87.photobucket.com/albums/k141/skipbo32/DSC03820.jpg

Olympus
September 17, 2010, 09:02 AM
Personally, I wouldn't go the woods and shoot at an animal at a distance I'd never even shot the rifle at on paper.

hometheaterman
September 17, 2010, 12:36 PM
If you want to shoot at 200 yards you need to sight it in for that. Just having it shoot high, may not get you hitting the right spot at further ranges. In my rifle, with reloads it has pretty close to the same POI at 100 and 150 yards. However, if I shoot Federal Power Shok ammo it hits about .5" low at 100 yards, but then at 150 yards about 3-4" low and about 2" to the right. This is just an example of how different ammo can shoot totally different, and you really need to sight in for what you are shooting at the range you are shooting. I also tried sighting my rifle in at 25 yards as the gun shop told me it would be dead on at 100 yards, and it actually was way too high. It was off target. I had to move to 50 yards after 25 and it was about 4" high. I lowered it to hit dead center at 50, then it was still high at 100 and I had to lower it some more. This is why I believe in shooting the actual range you plan to shoot when hunting.

DPris
September 17, 2010, 01:22 PM
Skip,
Nice rifle, as recently as 20 years ago I would have been willing to tote the weight, but I'm looking for light & easy in my declining years. :)

There are several factors to take into consideration in zeroing your gun, not the least of which is what are the average distances you might be likely to shoot it at. That's as important as the ballistics involved.

The .308 can easily engage as a practical matter (with good optics) well beyond 400 yards, but how often would you be shooting that far?

In a military context with your M1A, I might zero at 300 yards if I were using it in a designated marksman role as part of an infantry squad where its primary purpose would be for longer distances in open terrain.
In a hunting context, how often would you be taking a 300-yard+ shot?
Even here in Utah where we have a fair amount of open space between trees here & there, 300 yards would be far outside the norm.
In many dense forest areas where 50-75 yards is the norm, zeroing for 200 yards would be contra-indicated.

There are obvious exceptions, but the greatest majority of hunting shots are fired within 100 yards. Sighting your rifle to be able to put a bullet into a "guaranteed" spot at that distance, with the ability to carry out to 200 yards if needed, should cover you from 75-200, and that should handle 99% of the opportunities you may have at a deer or elk.

This again depends on what distances & what terrain you plan to hunt in.
If stand-hunting for deer or bear in an Eastern forest, or pig hunting a little farther South in heavy brush, a 50-yard zero could be a better choice. If antelope hunting in Wyoming or Utah, a 300-yard zero might be the way to go.

Evaluating what the rifle NEEDS to do is every bit as important as what the rifle CAN do, in terms of determining where to zero it.

Hometman puts it very well.
Match gun & load to actual distance. And- stick with the same load if you plan to be shooting farther out.

I test a bunch of guns every year, long & short.
Even at 25-yard handgun distances, besides the expected differences in elevation I also frequently run into some windage variations between different loads.
At the risk of repeating myself (I know- too late :)) you never know what a given load will do at a given distance until you shoot it at that distance. What it does at 25 yards is irrelevant beyond being anything more than a step in initially getting the gun & sights (or scope) on paper so you CAN hit at your preferred working distance & adjust accordingly. Same with 50 yards.

The old .30-30 guys could get away with buying whatever ammo was on sale over the years & still do well within the leverguns' 100-150-yard average working range, with familiarity of their guns, their distances, and their abilities.
You start getting much beyond that, and you need to get a little more picky about your equipment.

Denis

Olympus
September 17, 2010, 01:27 PM
This is why I believe in shooting the actual range you plan to shoot when hunting.

+1

The fact that you plan on using this rifle to hunt with is the biggest factor, IMO. You want the quickest, cleanest harvest that you can possible make when hunting. Taking a shot a distance you've never even attempted and basing it off of something you read in a ballistic chart is what I consider irresponsible and not sportsmanlike.

reddingshooter
January 27, 2013, 01:55 PM
man, technical data abounds!

i can tell you this. zero your 308 at 100 yards with whatever ammo your planing on hunting with, and keep what you have, or go buy a bunch out of the same exact lot number ,ect. bullet POA/POI can and does change significantly between lots. i work loads up for my guns and use the same everything in loading everytime, that is, unless i run out of a specific component such as power, then i rezero my weapon to the NEW LOT. most times it doesnt vary much but "not very much" at 100 yards can be 20ft at 300 yards. find a good load, zero your rifle to shoot flat at your most common shooting distances for your area, and then leave it alone. you should be fine in variances out beyond your common shooting distance

The_Armed_Therapist
January 27, 2013, 02:34 PM
About 20 yards if the front post is 1" above the bore; about 30 yards if the front post is 1.5" above the bore; about 40 yards if it's 2.0" above the bore.

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