January 18, 2008 at 11:01 pm #1323
I understand that gravity takes away from the trajectory when you’re shooting steeply up or down. How can I figure out where to aim on my mil-dot reticle?
ThanksJanuary 19, 2008 at 12:44 am #31977j3magnumParticipant
Google chairgun….actually a steep incline in either direction up or down will make a gun shoot high…January 19, 2008 at 1:19 am #31981
I have it and Simple Trajectory Program, but there are too many terms I’m unfamiliar with. Maybe I can give you some variables and you could help me from there…
The distance between the target up in a tree is about 30 yards. It is 15 yards straight, and 15 yards up from where I am shooting. Don’t worry about wind, the pellet I’m using, or anything too specific. The angle seems to be about 65Âº. This is just a guess using a protractor on a large scale. 😕
I tried this calculator :
I’m unclear on how I convert the “1.05 inches/3.72 M.O.A.” result I got into Mil-Dots.January 19, 2008 at 1:39 am #31984j3magnumParticipant
Jool heres a simple and pretty effective rool of thumb . If the distance to the tree is 15 yds shoot the target as 15 even if it is 30.. It has always been pretty close for me. If you have chairgun look at the lower left corner of the variable data screen there is a spot to input shot angle.Once you do this a second gray line will appear showing the hold for that angle…If you don’t have a chrony you can use chairgun to kinda estimate your pellets velocity..Shoot a target at lets say 25 yard and record how high or low the pellet hits or zero to that range. Now shoot a target at say 40 yards… Go to chairgun and pick the pellet your shooting and adjust the velocity until the trajectory path matches that of you 40 yard impact…now yo have an idea of the speed of you gun….input the angle of the shot ..you find that my rule will be pretty close. Remember to set your scope height ..on a talon it is 3 or 3 1/2″ depending on whether you have a tri-rail under you scope or not…January 19, 2008 at 4:57 am #31993
Thank you so much. I think I understand.January 19, 2008 at 5:39 am #31994
J3 is right on here! I use own an archery shop here in central Texas. In our out door silhouette shoots, we would use up-hill, down-hill shots to give the competitors a difficult shot. Most would naturally look at the visual distance. Most times they world shoot over. (Remember,you usually don’t have a ballistic computer in the field). I was very successful in the matches. The trick was to try to figure mentally the distance on a horizontal plane to the target. In other words, ignore the true distance to the target. Try to imagine a straight line below the target on the horizontal plane. The distance that would be exactly under the target if it were not on a steep incline. (Or visa-versa for a down hill shot.) Imagine a 100 foot tall tower. On the top of this tower is your pigeon. The shot is 100 ft. away= the 40 feet to the base of the target. As hard as it is to ignore the 100 ft. This is the correct way to do it. Only count the 40″ o the base. This is your true distance. It gets into gravity shear, and physics. And no it isn’t exact, but it will get you close. Like everything else, there is a point of diminishing return where this doesn’t work. Take for instance, just for fun. What if it is 40″ to the base, but the target in on a 1 mile high tower. Now what? well obviously tis isn’t going to work. Now if the you were on top of the tower, and shooting down, it will. Confused yet? This is where practice some where other than just a flat range comes in. Paper punching is informative, and fun. But it doesn’t replace field practice at different ranges, and types of terrain.
The other “TRICK” we would pull on competitors was to put a target only three to four feet in front of them, on the ground. You would be amazed how many experienced shooters would flat miss the target completely, Much less getting an X Shot!! In the heat of compitetion, they would totally forget to subtract the heigth of the sight from the arrow, or in our case the bore, from the target at this range. If the scope or sight is 3″ higher than the arrow, or bore, this us almost exactly how much low it will hit at this range. I love being sneeky! !!! But these are things we need to very often need in the field. Ever see a hunter try to hit a Texas Rattle coiled right in front of him. It can be a riot! Or try to put one into a not quite dead pigeons brain at 4 ft?
MikeJanuary 19, 2008 at 5:59 am #31997
Lol. I am learning some more equation and how to use these ballistic programs. It is fun and informative. I’ll even benefit from it with school work.January 19, 2008 at 8:37 pm #32029darkfrontParticipant
Well, while the effect may be that the POI is high, there’s a lot of geometry involved. It all happens because the effect of gravity is based on the horizontal distance the projectile travels, not the angled hypotenuse of the triangle formed between you and the target.
Some ballistics programs will help you get a feel for it, but if you’re in the field without a computer, multiply the actual distance (from your rangefinder or mil-dot calculations) by the following multipliers, based on the angle of incline/decline.
Once you’ve multiplied the distance by the multiplier, confirm the dope for your shot for that new distance, and adjust scope and/or compensate with appropriate mils.
Ex: Target is 200 yds away, but at a 30Â° incline.
200yds x 0.87 = 174 yds.
Treat the shot now like a 174 yd shot.
90 0.00January 20, 2008 at 12:22 am #32046
Great Info! Now If I can just get those deer to stand still long enough for me to make the calculations!January 20, 2008 at 12:27 am #32048libertyman777Participant
Yep. This is why long range rifleman rely on items like this to compensate for ranging errors for sighting along incline/decline slopes.
I’m not really sure it a tool like this would be warranted for airgun distances.
I have a pond behind my house that has a decline angle of ~20 degrees with no way to shoot any horizontal range equivalent with a laser range finder. The visual range to the target was 102 yards. So I guessed at the angle and by shooting, determined that the range was horizontally 96 yards. With my .22 rimfire shooting subsonics, that was a full minute of elevation difference in range and enough for a miss.
It shouldn’t be too hard to teach yourself the important angles and the correction for each, by using Darkfront’s table for correction. You can make your own table by taking the angle in degrees and then hitting the Cosine key on your scientific calculator. This will give you the multipliers listed in the table above.
You can estimate:
45 degrees is half way between horizontal and vertical. Split 45 in half and you have 22.5 degrees and 67.5. At airgun distances this should get you in the ball park. Type those numbers into to calculator, hit cosine and wallaaah, you’ve got three easy, common corrections with enough rotational distance between each to keep from getting mixed up.
A cost effective was to learn estimation is to buy a protractor (a large, plastic one will work great). Attach a line at the center of the flat side and hang a small weight at the end. Then you can roll the protractor back and forth with the curved portion toward the ground. The taunt line will mark the angle to give you a feel for it. Kinda like judging distances, it just takes practice.
Or if you’re into neat stuff then buy the Angle Cosine indicator. You can get the indicator and the scope tube mount for under $125. The indicator is easy enough to find and here’s a link for the mount. http://www.ustacticalsupply.com/index.asp?PageAction=VIEWPROD&ProdID=391
PaulJanuary 21, 2008 at 12:16 am #32102darkfrontParticipant
Hey knifemaker, if you’re hunting from a stand, you can always do preset calculations by ranging and correcting before the hunting season, using landmarks like specific rocks or trees and drawing a picture of your field of view and writing in the appropriate distances in your field book. Should make your estimation faster.January 21, 2008 at 1:15 am #32104
As we say in Texas, “You Know Thats Right”!!!! Been there and done that! Especially for bow Season. It’s those unexpected long range quick opportunity shots that can get you into trouble. This is where practice and learning what the old folks called Kentucky windage. There was much more to the skill than just the wind. A lot more. But in todays age, not many people get to shoot at many varying distances and elevations to get use to it to the point that it is virtually automatic. having grown up in the mountains of Ala. and Tenn. It is something I learned at an early age. It just comes naturally to me. Just as natural as judging the difference between 200 yd. and 4oo yds with a rifle, or 20 yds. and 40. yds with a bow. I wish everyone could have had the opportunity to walk the woods fields, hills and draws the way we did growing up. Where carrying a rifle or pistol was just a way of life. Not looked down on at all. Just a natural part of life. We never had the problems of the inner city, or experienced crime. Living in the city as I do now is a totally different. I still carry everyday, but in a different world. Thank goodness, as it has served myself and others well. Mike
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