How to judge MOA adjustments for various yardages? Excuse stupidity of question.

[BigBlueEyedDevil]

I was watching a sniper in "Saving Private Ryan" tonight and I was wondering how I'm going to learn to make the various MOA adjustments on my scope for target shooting.

I have a Savage 10FP with a Leupold 4-12x40. I don't have the slightest clue on how to make different adjustments after I get the scope sighted in.

For example, If I want to take a 500 yard shot, how do I know how many clicks of elevation and windage to make if my scope is sighted for 100 yards???

Thanks for the help and putting up with my sophomoric question.

 

[Zak Smith]

Here are three exemplary methods:

1. Get a 100y zero, then start shooting at a 500 yard target. Record how many MOA elevation you used to get there.

2. If you are shooting a standard load in a standard caliber, you can check the published literature.

3. What most people into this kind of thing do: Run a computer program which will take as input the environmental conditions (elevation, temp, etc), the bullet muzzle velocity and ballistic coefficient, and primary zero, and give you a table of MOA drop at 25-50 yard intervals along with the windage MOA required for a 10mph wind.

Once you develop this table, you can string it to your scope or tape it to your stock.

Having external elevation & windage knobs (ie, no caps) is particularly useful.

 

[Dave P]

http://www.norma.cc/

Norma has a decent ballistic calculator here.

 

[BillL223]

I use the Sierra Infinity program which is available for about $40. It allows you to get output directly in 1/4 moa increments which is the normal scope "click". In all of these programs, you need to know your velocity and your bullet BC but you can get close with the ammo mfgrs figures. Stoney Point makes after market target knobs which work wellif your scope doesn't have them, most don't. I always confirm with actual range results. Another technique is to use "Point Blank Range" This also varies by velocity and bullet BC and can be found in some reloading manuals. Basically you zero at some predetermined range and your bullet will always be within a certain number of inches above or below, usually 3".

 

[ocabj]

http://www.eskimo.com/~jbm/calculations/traj/traj.html

JBM is a CGI program you can run on your own webserver, but the above link works.

If you know your muzzle velocity, the ballistic coefficient of the bullet, then it can give you the dope for how many minutes difference at various distances.

Note that this isn't in stone. Sometimes what you experience in real life is different than what the program tells you. Various factors can come into play including wind, shooting stance/position, type of rest (sling, bipod, pedestal), elevation with respects to sea level, humidity, barometric pressure, etc.

For example, I have 44.6gr Hodgdon Varget pushing a 175gr Sierra MatchKing at 2775fps (clean cold bore) and 2825fps (warm/fouled bore) with a BC of .505. I plugged in the data with a 100 yard zero and it stated that I would need 13.4 MOA of adjustment for 600 yards. When I shot this load at a 600 yard match, I found that on that particular day, I only needed roughly 12MOA elevation adjustment for 600 yards from my 100 yard zero.

So use JBM to work up an estimated dope, then confirm it with live shooting.

 

[30Cal]

ocabj pretty much hit the nail on the head. Ballistics calculators are better than guessing but are no substitute for actual shots fired data.

The other thing to consider is that there is a lot of estimating on your part that is going to derail the 76.24" correction that you read off the chart. How well can you estimate range and how accurate is your wind estimate? If you can put a bracket around your estimation errors (I can judge ranges to within 10% and wind within 3mph) then you can look back at your chart and see what your limitations are (ie at what range will you start to miss due to errors in wind or range estimation).

Ty

 

[theCZ]

you said it, ocabj. I look up how much drop my gun should have in manuals, and use the programs to see what they say. So far, they've been off by at least an inch at 200 yards, and 2 to 5 inches at 300. That sure ain't good enough for me or the varmints I'm shooting.

There really is no substitute for sighting in at a preferred range, and shooting to see drop from there. You'll be suprised at how much difference there can be even with the same amount of gunpowder and the same weight bullet, but a different type (ie matchking vs blitzking).

 

[Jim Watson]

Agreed.

Bullet companies seem optimistic about their ballistic coefficients, ammo companies and loading manuals are definitely optimistic about their velocities. A computer or chart will get you in the vicinity, but there is no substitute for shooting. You can then make up a real chart for YOUR ammo in YOUR rifle.
Change something and do some more shooting. Tough job, isn't it?