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Old 29th January 2016, 04:17 PM
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Brian.Samson Brian.Samson is offline
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Join Date: Jun 2009
Member of: Pontefract, Doncaster Airgun Range
Location: Doncaster
Posts: 2,324

Originally Posted by verminator View Post
Right, it completely fails below 15 yards. To be honest I had not heard of the 15s rule until this discussion and I thank the forum members for their patience explaining it to me. I have always measured it.

The 15s rule is clearly a good approximation and will do for most, but what I'm after is an accurate mathematical model that works from 8 yards onwards.

The discussion on this forum has given me some ideas for further investigation, I just wish the wind would go away.

Well at least someone agrees

I think what you said was... if you used the diagonal distance (which is what you should use) it would be 1/4 of a mildot out.

When you quote figures in mildots like that it sounds like a lot - wow - a 1/4 of a mildot!!...

Actually a 1/4 of a mildot at 11 yards is less than half a pellet width. So if you just aimed exactly how you would have done if the target was on the level, you would hit half a pellet width high. That gives you plenty of leeway to take down a 15mm kill.

The rule of 15's is a quick way to tell whether you need to aim off or not. If it's below 15 yards OR it's below 15 degrees - you can forget about the angle, because the difference it makes is tiny and isn't worth worrying about.

Explain to me how this "Completely Fails" ? - Ah, are you talking about the Rifleman's rule when you say it completely fails? Yes it does, you're right.

The Rule of 15's will get you close enough to the correct answer never to have to worry about an angle or a mathematical model again.

Less than 15 yards OR less than 15 degrees - just aim in the same place you would have done if it was on the level. (taking the diagonal distance)
More than 15 yards AND more than 15 degrees - aim inside bottom of kill and in most of the cases you'll ever see in an HFT competition, that will be enough to take the target down without worrying about angles.

The mathematical formula for this is very complex, it's not the sort of equation you can do in your head, but if you tell me your MV and the BC of your pellet, I'll give you a spreadsheet with every angle and every range on it and tell you how much higher your pellet will hit. You can print that spreadsheet out, laminate it and carry it round with you if it makes you feel better.

Everyone else will just be using the rule of 15's and not worrying about the angle, but at least you'll stand out from the crowd.

Last edited by Brian.Samson; 29th January 2016 at 04:26 PM.
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