Sighting In ... More Questions

[Jeff Thomas]

Most of this will relate to rifles, but I put this thread in General Discussion because I believe the same lessons will aid for sighting in pistols and shotguns (with slugs).


I don't remember the term, but I do remember that the choice of range for sighting in seems to depend upon intended use, the round / cartridge used, and the idea that the bullet will rise and fall roughly an equal amount in its arc (?). That is, if I'm sighting in a .22LR rifle at 100 yards (per the Federal ammunition web site), I'll be 2.7 inches high at 50 yards, and 10.8 inches low at 150 yards. Thus, I gather, it might be better to sight in a .22 at about 75 yards ... ?


And, is there a handy book or software program to use when sighting in with different factory loads (giving data similar to the Federal web site?)? I'm trying to get to the point that I really understand the theory well enough that I could efficiently sight in any firearm, and not need to dumbly refer to instructions everytime. I suppose I simply want to better understand the basic principles involved ... just to better educate myself.

Obviously, I'm still pretty green with this stuff, and don't get anywhere near reloading yet. Still becoming familiar with different kinds of iron and optical sights, as well as how to adjust each of them. Thanks for your advice ... I'm always impressed about how much there is to learn in this field.

I suppose another thing I should do is become more familiar with the different groups within the Arizona Rifle and Pistol Association - a day or two with some of those folks would probably do wonders for my knowledge.

Thanks for your help. Regards from AZ

 

[Mikey]

Exterior Ballistics Tables

I believe what you are alluding to is the "mid-range trajectory" (hereafter called MRT) of a particular rifle+catridge+load. A book called American Ammunition and Ballistics, by Ed Matunas, covers the thoery of sighting-in based on MRT and the acceptable deviation from point-of-aim (hereafter called POA).

MRT is the highest point above the POA that a bullet will rise when the sight in distance is known. Bullets don't travel in a level path. They start out below the sighting plane (in the barrel) and are launched slightly upward so they cross the sighting plane twice - once at relatively short distance and again (due to gravity) at the sight-in distance. Prior to reaching the sight-in distance, the bullet will rise above the sighting plane to a maximum height based on it's ballistic coefficient and velocity. This makes these sight-in distance selections very specific to a certain cartridge/bullet combination.

An example (using purely fictitious figures since the book is at work) would be like:

You have selected the .243 Win with Rem 100 gr PSP as your ammo and you want to hunt white-tailed deer. The tables in the book give the mid-range trajectory for that load for varying sight-in distances. The sure kill zone on a white-tail is about 10" (lung shot). You will aim for it's center so that gives an acceptable deviation of +/-5". But you also have to account for your particular guns accuracy with that load under hunting conditions. We'll say you can hold a 4" group at 100 yards from a hunting type supported position. That takes another +/-2" from the acceptable deviation so now you look in the tables for a sight-in distance where the MRT is less than (or equal to) 3". You also look for the distance where the bullet drops 3" below the sighting plane. We'll say that the tables show a sight-in at 250 yards produces a MRT of 2.7" and the bullet drops 3" below the sight plane at 325 yards. Thus sighted, your rifle and load are at their optimum for the chosen target and you can take a "dead-on" shot at any deer that is at 325 yards or less.

Obviously, if any of the variables change (target size, new load, etc), you must re-calculate your optimum sight in based on the different information.

The information contained in Matunas' book is available from lots of sources but I haven't been looking for them so I can't point you toward a source. Just look for anything related to Exterior Ballistics Tables. I think Sierra Bulletsmiths has a program available and Hornady may as well. Most of the calculations require that you know the bullet's Ballistic Coefficient (BC) and starting velocity.

Hope I have helped. It's an interesting subject once you understand it.

Mikey

 

[C.R.Sam]

Mikey speek true.

If you are into additional brain massaging, imagine a bowling ball falling off of the roof of your house. Any bullet falls earthward at about the same rate. Takes time for the bullet to get to the target. How far will a dropped from hand bullet fall in that amount of time. The amount the bullet falls per foot traveled toward the target increases with range since the bullet is traveling at it's fastest at the instant of leaving the muzzle and decelerates on it's way toward the target. IE; bullet falls more between two hundred yards and three hundred yards than it does between one hundred yards and two hundred yards. It is going slower during the second leg but still falling at the same rate.

Sam..feel free to take two motrin and hit me.

 

[dZ]

here are some links:

http://www.perry-systems.com/calculator.htm
Exbal Features:

Exbal is for target shooters, varmint hunters, high power competitors, tactical military and law enforcement, and long distance shooters. It accurately determines
where your bullet will go in relation to line of sight. It performs rigorous three dimensional motion equation calculations that account for air resistance, gravity, and
wind drift.

Exbal can utilize multiple ballistic coefficients needed to characterize high efficiency target and boat-tail bullets such as the Sierra MatchKing.

You can specify one set of atmospheric conditions for sight in, and another set for a different range or hunting location.

Exbal does not require a lot of memory or disk space. It can be loaded on a laptop computer to take to the match with you.

Exbal System Requirements:

Operating system: Windows 95, 98, NT 4.0, Windows 2000

Disk Space: Less than 1 Mb

Graphics: VGA

http://www.dexadine.com/ballisti.htm
Ballistic Explorer™ is the finest exterior ballistics software on the market and the only external ballistics software you need. Whether hunting, target shooting, or
competition shooting you need to know the ballistic performance of your factory ammo or handloads all the way to the target, and only full featured ballistics
software can give you the answers you need.

http://www.gmdr.com/rcbs/rcbstext5.htm
For that very small and select community interested strictly in internal ballistics, what happens to the bullet after leaving the gun's muzzle, is of little interest. For the rest of us, hunters, paper punchers or
plinkers, the trajectory of that bullet is of vital interest - it's what "gunning" is all about. RCBS.Load provides one of the industry's most complete and accurate external ballistics calculator (XBC)

http://users.erols.com/twool/ballistic1.htm
F=MA^2 Ballistics Calculator v1.1 by Thomas A. Woolman, Copyright 1998 On Target Technologies, Inc.

This JavaScript Program will accept the weight of a bullet (in grains) and it's velocity (in feet/second) and will output the resulting energy contained by that bullet in
Pounds per Square Foot.
>>>>>>>>>>>>>>>>>>>
Recoil Calculator v1.1 by Thomas A. Woolman, Copyright 1998 On Target Technologies, Inc.

This Program will accept the weight of a bullet and powder charge (grains) and the bullet muzzle velocity (feet/second) and the weight of the weapon in pounds, and
will output the recoil energy generated by the fired cartridge in foot/pounds.

http://www.zvis.com/bvjtools.shtml

Here you can find the results of my experiments and researches in Ballistics & Java programming language. Basically some ballistic formulas interpreted in java. IMHO this is where Java is good,
small applets for some nice animation effects & calculations.

 

[Art Eatman]

And, by and large, zeroing a .22 rimfire rifle at 75 yards is about as good as it gets, for general purpose shooting.

, Art

 

[Jeff Thomas]

Wow ... Ph.D.'s in ballistics ...

Thank you very much! What a tremendous help. I've been rereading your posts, and looking over those web sites.

To my inexperienced eyes, RCBS.Load and Ballistic Explorer seem to be the most complete programs ... your thoughts? [My initial uses would be sighting in various firearms, but I'd also like a program that I can use when I begin reloading, and perhaps some competition as well.] A bit more expensive than some, but still pretty cheap relative to ammo, firearms, etc. I gather these programs will already have lots of data (including ballistic coefficients). I can understand how I can measure all of the other variables, but knowing the ballistic coefficient seems a bit trickier in some cases, no? I suppose for competitors that data is readily available, but I assume if you're using surplus or other cheap ammo you simply estimate the coefficient?

I also noticed this helpful thread over in Rifle - http://www.thefiringline.com/forums/showthread.php?threadid=51096 . And, someone posted this site for more ballistics software ... http://www.lascruces.com/~jbm/software/software.html

Thanks again. Regards from AZ