Sighting in your rifle

A series of articles and tutorials to help you hone your outdoor skills

Sighting in your rifle

Postby Jeremie76 » Sun Nov 09, 2008 10:23 pm

I accidently posted this in Guns and couldn't figure out how to delete it, so I posted it twice.

A friend of mine gave me some of this information and I thought I would pass it on.

There are some rumors about sighting in your rifle that you don't want to believe.
Here's a few of the funnier one's I've heard lately:
1. Bullets rise once they leave the barrel - Sorry, but no. Gravity is constant!
2. Scope height doesn't matter - You'll see later line of sight is important!!
3. You need to sight your scope to shoot low at 100 yards since bullets rise (told to a guy on a hunting sight I go to, and this was told to him by a Bass Pro Shops employee).

Now there are a few important concepts to understand as follows:
Four terms to know when properly sighting in a rifle.

1. Point Blank Range; Point blank range when sighting in a rifle is the first point at which the line of sight intersects with the bullets path in the bullets trajectory arc.

2. Mid-Range Rise; Mid-range rise when sighting in a rifle is the highest point in the bullets trajectory between the point blank range and the true zero point.

3. True Zero; True zero when sighting in a rifle is the second point at which the line of sight intersects with the bullets path in the bullets trajectory arc.

4. Maximum Point Blank Range; Maximum point blank range when sighting in a rifle is the height of the mid-range rise and the bullet drop beyond true zero, both are equal in measure.

Some information along with some graphs can help if you go to http://www.gunnersden.com/index.htm.sightin.html

The reason a lot of people think that bullets rise is because the scope itself must be pointed downward to intersect the bullet's path! The bullet actually crosses the line once at Point Blank range, then continues on in more of an arc causing the bullet to appear to rise. The bullet finally intersects the line of sight again at the point most of us are familiar with, which is true zero.

Now here's where things get interesting, most of the folks I know zero their rifle for 200 yards, then compensate if the shot is shorter or longer than that. The key here is to understand where the mid range rise and maximum point blank range fall. By understanding these two points, you'll know that you can aim dead on at a much further distance than what you've actually zero'd in at.

Let's understand mid range rise first. During the arc of the bullet's trajectory, the bullet fly above the line of sight to some maximum before starting to fall. Let's say that the bullet flies 3" above the line of sight at 75 yards and then begins its descent. The bullet crosses the line of sight again at 200 yards (cause that's how we set it) and continues then to fall below line of sight. Let's say then that the bullet drops another 3" at 275 yards. The bullet will have spanned 6" of vertical total from 75 to 275 yards, that means the bullet will hit 3" high of the center of an elk's vitals at 75 yards, and 3" low of the center of a elk's vitals at 275 yards, both of these are well within effective killing area.

I'm not sure about the rest of you, but 300 yards is about as far as I'd consider shooting. Knowing that, I no longer have to adjust for bullet drop anywhere in between there, just aim dead on!

Keep in mind the factors that would effect this equation such as flatter shooting bullets will give a longer maximum point blank range (yes, feel free to use this excuse when justifying the purchase of a new gun, my wife didn't buy it), higher scope rings will create a steeper line of sight for the scope affecting mid range rise.

Shooting at different distances will help you determine your bullet's mid range rise since that's a hard one to calcuate, but you may want to start at 50, then move to 100 to see where they hit.

On another note, after a guy I know had a fiasco of missing a deer at 100 yards, he loaded up 3 sets of identical 30.06 bullets with the same primers, bullets, and shells, but 55,56, and 57 grains of powder. The results were amazing. The 55's all hit within a dime a little to the right of center. Add one grain, they went wild! almost a 2" spread and 4 full inches to the right! Add another grain, they came back left but had a 1 7/8" spread. A few rounds of factory ammo too and he was disappointed to see another 1.5" spread.

Don't be afraid to try different ammos to see what your gun likes. Also don't be afraid to experiment with some hand loads as well!!
"I have been driven many times upon my knees by the overwhelming conviction that I had nowhere else to turn" - Abraham Lincoln
Jeremie76
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Postby richard_a » Thu Aug 25, 2011 9:30 pm

Just sighted in my Winchester M70.

Discovered something I didn't know.

The crosshairs on my Burris scope stick!

I was shooting a little low --- so turned the scope 6 clicks up ---- and nothing changed.

Then, a veteran shooter told me, "tap the scope lightly - just a few times." I did ---- and suddenly, I was shooting dead on.

My M70 easily shoots 1" groups at 100 yds ---- (no tripod, etc --- bare hand shooting).
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Postby Lizette » Mon Aug 27, 2012 7:13 am

As you begin shooting, be sure to analyze and record each shot.
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