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View Full Version : So, How Do You Determine the Correct Range for Sighting?


Jeff Thomas
January 1, 2000, 02:21 PM
I assume that experienced shooters have basic 'rules' for the distances you'll use to sight in various firearms, no? I gather sidearms would be sighted in at 25 yards, and in my tactical carbine class I think we used 50 yards, as I recall (supposedly kept a decent group out to 200 yards, no?). But how about a .22 rimfire, a shotgun with slugs, or a .308, or ????

I would assume it all depends upon the useful distance of the ammunition involved, but aren't there some basic rules of thumb I can memorize?

I read the 'Did I Sight It In Correctly?' thread, and there was lots of good advice there as well. Thanks.

Regards from AZ

[This message has been edited by Jeff Thomas (edited January 01, 2000).]

labgrade
January 1, 2000, 03:49 PM
The idea is called "maximum point blank range." Using a deer scenario, you've got an (for use of argument) approximate 6" vital zone. You want your rifle (whatever) sighted in so that the bullet never departs more than -3" to +3" from crosshairs (line of sight).

Coming off the top of my head - say a 30-06, 180 spitzer at 2700fps ... sighted in at +2.5" would give you a maximum point blank range to ~280yds or so. (Please don't hammer me on the #s as it's just a good guess to demostrate the principle).

The bullet starts under the line of sight (usually ~1.5" & crosses LoS at ~25-30yds ... probably about +2" or so at 200 and dead on at 250, continues to drop (figuratively) at would reach the -3" from LoS at about 280 or so.

Sighting the rifle in in this manner allows you to just point the crosshairs on what you want to hit (+/-3" is no big deal due to size of vital zone).

Bullets with more rainbow trajectory require, either larger vital zones or shorter maximum point blank range.

Too, depending upon caliber/shooting platform, attempting to set up a long distance maximum point blank range may be foolish just because that Cal/platform isn't going to be very effective at the longer ranges anyway. As in the .17 Rem (which is relatively flat-shooting) but not effective for elk (with a 7-10" vital zone. You would moreso want to set it up for ~3-4 (+/-1.5-2") for the varmits, etc.

Again, the 30-06 #s above for explanation only ... if you need some exacts, reply again with what you've got & I'll run some of your real #s through a ballistic program & give more exact info.

Bud Helms
January 1, 2000, 08:23 PM
Labgrade is absolutely correct and giving good advice.

Think of a tube extending out from the muzzle of your rifle with the longitudinal center line of the tube exactly inline with the bore line of the barrel and with a diameter as wide as the vital area of the game you're hunting. Say, for example, three inches for a whitetail.

If you take your bullet weight and muzzle velocity to a trajectory table, you will find the vertical rise and fall from bore line as the bullet passes down range. The better trajectory tables include type of bullet (shape) or BC, but weight and velocity are the key parameters.

Now the question is: How far can the bullet travel out of the muzzle and remain inside the tube? The answer is your point blank range. This is important to know because that is the range at which you can lay the crosshairs on the center of the vital area and stay inside it (the three inch circle in this case).

Labgrade gave a good example with his numbers. Gotta be close. But let's say you are hunting game with a larger vital area. Or maybe you hust want to allow yourself a larger vital area on the same whitetail. Say a five inch diameter circle. You just extended your point blank range. Go back into the trajectory table and see how far down range the bullet stays in a five inch tube (rise and fall from boreline).

Now all you have to worry about is down range energy. You want to maintain enough energy to make a clean kill. A ten inch point blank range tube for a 30-06 wouldn't leave enough energy to be sure of a clean kill and still not have to hold high.

Most good hunters/shooters go for as small a vital area as they can reasonably expect to hit throughout their point blank range, for two reasons.

1) The smaller the diameter of the point blank range tube, the shorter the point blank range and the more deliverable energy on target (because you will be targeting at a closer range with the same rifle) and

2) Shooting off hand, as you often must in a hunting situation, even though you are aiming for the center of the vital area, your point of aim will probably wander about some.
If you don't know the exact distance to the target, you still should know your point blank range and you know you'll hit somewhere in that theoretical circle. But the whole circle is moving around! So even if you keep the point where you want to put the bullet somewhere in the circle, the moving circle is covering an area that can be described as a six inch diameter circle! Draw a circle six inches in diameter on a piece of paper and cut out a three inch diameter circle from another piece of paper. Roll the three inch circle around the inside of the six inch circle. The three inch circle is always touching the circumference of the six inch circle and its center. That's your three inch point blank circle wandering around but never completely leaving the center of the vital area.

That is why you shoot from the best rest you can, circumstances allowing, and why you limit the theoretical point blank range you use to include the practical situations of the woods. Keep the point blank range tube diameter to slightly larger than the group you shoot at the range targets off bags. If you are shooting a 1 1/2 inch group consistently, use a point blank range derived from a 1 1/2 to 2 inch rise and fall from boreline ... 3 inches at the most.

It doesn't take nearly as long to visualize it and use it as it takes to describe it in words.

Sensop

OkieGentleman
January 2, 2000, 12:02 AM
To complicate the matter more, try this scenerio.

You are going to hunt deer in mixed country (wooded with large open areas).

For the sake of the discussion we are using a 308.

You sight in your rifle for 100 mtrs with the heaviest bullet you can find. Now take the lightest bullet in 308 and shoot it without moving your sights and see where it hits, you might be suprised to find you are zeroed in for about 200 mtrs.

Now when you go hunting in a mixture of brush and open country, you load 2 rounds of light bullet first then one with a heavy bullet in the clip and a heavy bullet in the chamber.

If you move out of the heavy brush, you jack the first two rounds out and put them in your pocket. You now have one long distance round in the chamber and one in the clip.

Why two rounds of heavy? In the brush the heavier bullet will not be deflected by leaves or twigs like a lighter bullet will. And at best in heavy brush you won't be able to see to get more than one good shot anyway.

Why two rounds of light? In open country you might get to shoot twice, hopefully you wont need to if you placed your bullet properly.

How do you keep track of what is what? Color the bullets with magic marker. Blue for heavy and green for light.

Before you guys flame me go and check your ballist tables and see if I am wrong.

Jeff Thomas
January 2, 2000, 12:42 AM
You guys are great - thank you very much. This is definitely an 'advanced' course for me, compared to what I had learned to date regarding sighting in.

Now, it looks like I could use a ballistics program and / or trajectory tables to take this further. Can you recommend such a program, and / or a source for the tables?

Are sidearms a bit easier? Is 25 yards the simple answer for all but hunting purposes?

Thanks again. Sometimes I think Rich ought to call this TFL University. ;)

labgrade
January 2, 2000, 10:25 AM
Jeff,

I run an Oehler Ballistics Explorer. Fairly "basic" but that's very relative in what you can do with it ... tons of info! Other programs about too & all should serve you well.

Okie,

No flames, but your scenario's not quite right (always) ... it very much so depends on velocities achieved. I've a .309 JDJ T/C & a M7 .308 ... have fired & chrono'd 3 various loads from each - 150s, 165s & 180s.
Running the loads thru the puter, it turns out that the 165s (at the velocities I get from these two shooters - ~2400fps) actually are flatter shooting (to 300yds) & maintain better downrange energy. The differences are pretty minimal (inch or so at 300 & a "few" pounds) & probably wouldn't make a whit's difference in the field, but the 165s are more accurate so that's where I ended up.
There are some muzzle velocity windows in which different weight bulletsperform better. If I was pushing the 180s another 300-400fps faster, I'd use them due to the "better" exterior ballistics.

I believe the "heavier bullets for busting brush" is a misconception.

Unless tinkering, I usually work up one bullet/powder combo for any particular shooter & just stick with that for all uses.
Mixing & matching in the field's just not my cup of tea, but I'm old fashioned.

Lot's to be said for the old saying - "beware the man with one gun, he probably knows how to use it."

bergie
January 2, 2000, 01:35 PM
Jeff T
Some of the ammo companies put out leaflets or brochures with info about their lines of ammo including velocities, trajectories, etc. Your local gunshop probably has a bunch of these in a rack. Some have the "point blank" tables some don't. This info is also published in books such as the Shooter's Bible and tear out multipage ads in many of the gun or hunting magazines in the early fall.
I grabbed one off the shelf, and since you mentioned .308 here are some #s, the one I grabbed didn't have the "point blank" so this is basic ballistics for Federal Premium 165 grn boat-tail soft point from a 24" test barrel
m.v. = 2700fps
energy = 2670ft/lbs at the muzzle
with sights 1.5" above the bore line and zeroed at 100 yds, the trajectory is such that:
50 yds= -0.1" 100yds=0 200yds=-4.0 300yds= -14.4"
with a 200 yd zero
50=+0.9 100=+2.0 200=0 300=-8.4 400=-24.3

The 2 1/2" high at 100 yds that was mentioned is a good general zero for some of the common hunting calibers (.270, .308, .30-06 and a few others) that will give a dead on hold for out close to 300yds. Of course it is up to each individual shooter to determine his needs, evalute his equipment, practice, practice, practice, and make the necessary adjustments.
Good shootin,
Bergie


[This message has been edited by bergie (edited January 02, 2000).]

OkieGentleman
January 3, 2000, 11:32 PM
No problem Labgrade. The scenerio I was proposing was with off the self ammo.
Your right tho if you have the equipment and go to the trouble of working up the bullet/powder combination that a particlar rifle shoots best that is the one to stick with. My favorite times on the range have been test firing new loads to get the maximum out of a particlar weapon.
Jeff working up different loads for a weapon and finding the "sweet spot" with a particlar gun is 3/4 of the fun of reloading.
Now ask about barrel vibration and how it affects the bullet placement on the target and watch the fun begin. BIG GRIN

Bud Helms
January 6, 2000, 10:16 PM
Jeff,

In regards to your follow-up question about "sidearms", Self defense and hunting handgun sight-in problems are the same but different ... succinct, huh?

Every one needs to know the mechanical accuracy of their handguns ... their inherent accuracy without you on the trigger. That's what shooting a rifle off a rest tries to do.

Those who can afford to buy or can borrow a Ransom Rest (brand name) come the closest to determining that. The rest of us try to figure out a way to get as steady as possible and squeeeeeeeze. That said ...

Hunting handguns should be sighted in the same way as rifles. That's it. They're used the same way, in the same situations. You just have different ballistic realities to deal with.

A self defense handgun ... well there is a forum here for that, but what I do is sight it in just like any thing else (at 20 - 25 meters), check group size at 10 - 12 meters and then learn to shoot it in a "defensive/protective" mode and learn to hit something. That might seem like an obvious statement, but you only need to be accurate to a practical degree, fast and repetitive. No squeeeeeezing rounds off here!

I day dream of being able to afford to go to Gunsite or Thunder Ranch one day. In the mean time, I listen, read and practice, practice, practice, practice, practice, practice, practice ...... at ten strides from the target. :) (I'm hell at 10 meters ... ha!)

Sensop

[This message has been edited by sensop (edited January 06, 2000).]

[This message has been edited by sensop (edited January 06, 2000).]

Bud Helms
January 6, 2000, 10:17 PM
Double post ... edit/delete

Sensop

[This message has been edited by sensop (edited January 06, 2000).]