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Posted: 12/21/2014 3:08:34 PM EDT
[Last Edit: blackfly53]
I have a little private range I use from time to time which is flat for about 65yds in an area. I assembled a precision AR and have 125yds available but it requires me to go up a hill. I would say I am approximately 50-60ft above the target so to speak.
Question, how does that effect trajectory? I need to rezero for 100yds and don't want to be off when I go to a flat area. Does it matter?? Also Im throwing 77grn lead out of an 18" WOA barrel. |
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Posted: 12/21/2014 3:11:46 PM EDT
[#1]
At that distance, your point of impact will be about 1/64th of an inch off where it would be if you were shooting flat-ground.
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Posted: 12/21/2014 3:23:08 PM EDT
[#2]
So safe to say that at 200yds it will be double? If I can use that particular setup to get me on the money, when I get to flat ground I may require a slight adjustment it seems.
Thanks! |
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Posted: 12/21/2014 3:37:17 PM EDT
[Last Edit: ReconB4]
[#3]
http://www.midwayusa.com/product/615767/badger-ordnance-angle-cosine-indicator-kit-with-generation-2-picatinny-style-mount-aluminum-matte
Something like this will help you find the angle you are shooting. It will give you the cosine to figure out the true distance. The only other way to be sure is to use a range finder that corrects for the angle of decline. You will confuse people by talking like that. You shouldn't say true distance. Oh nvm... |
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Posted: 12/21/2014 4:06:09 PM EDT
[#4]
Shooting uphill or downhill point of impact will both be higher than flat and level.
At 125 or so with a fairly flat shooting 5.56 it is an game of mathematics more than anything you have to allow for. 50 feet isn't much of an angle at 125yds As the angle becomes steeper , distance becomes greater or the cartridge has more shapely trajectory you have to allow some. A 45/70 shooting 300 yds down into a 200 foot deep valley might be several feet difference (just a guess) This is something quite importaint for bow hunters |
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Posted: 12/21/2014 4:59:32 PM EDT
[#5]
Quote HistoryOriginally Posted By blackfly53:
So safe to say that at 200yds it will be double? If I can use that particular setup to get me on the money, when I get to flat ground I may require a slight adjustment it seems. Thanks! See: https://www.google.com/#q=trajectory+calculator |
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Posted: 12/21/2014 5:20:41 PM EDT
[#6]
Level ground
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Posted: 12/21/2014 5:21:14 PM EDT
[#7]
15 degree angle
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Posted: 12/21/2014 5:21:45 PM EDT
[#8]
45 degrees
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Posted: 12/21/2014 5:48:42 PM EDT
[#9]
Interesting. Thanks for the info!
Sooo glad this sub forum was added. |
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Posted: 12/21/2014 6:07:30 PM EDT
[#10]
At distances past PBR, aim lower -generally speaking.
The steeper the terrain, the less the drop of the projectile. |
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Posted: 12/21/2014 6:11:31 PM EDT
[Last Edit: W_E_G]
[#11]
Quote HistoryOriginally Posted By Powderfinger:
At distances past PBR, aim lower -generally speaking. The steeper the terrain, the less the drop of the projectile. Only true for extreme distance shots. If the point of impact is only changed a measly half-inch on a 45-degree 100-yard shot (say from the rooftop) of a high-rise apartment building. during the zombie apocalypse, are you really going to try to hold a half-inch lower with your 3 MOA Aipmpoint? Any shot you might make off the roof of your trailer will require no correction. |
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Posted: 12/21/2014 7:37:16 PM EDT
[#12]
Quote HistoryOriginally Posted By W_E_G:
Only true for extreme distance shots. If the point of impact is only changed a measly half-inch on a 45-degree 100-yard shot (say from the rooftop) of a high-rise apartment building. during the zombie apocalypse, are you really going to try to hold a half-inch lower with your 3 MOA Aipmpoint? Any shot you might make off the roof of your trailer will require no correction. Quote HistoryOriginally Posted By W_E_G:
Originally Posted By Powderfinger:
At distances past PBR, aim lower -generally speaking. The steeper the terrain, the less the drop of the projectile. Only true for extreme distance shots. If the point of impact is only changed a measly half-inch on a 45-degree 100-yard shot (say from the rooftop) of a high-rise apartment building. during the zombie apocalypse, are you really going to try to hold a half-inch lower with your 3 MOA Aipmpoint? Any shot you might make off the roof of your trailer will require no correction. You are a funny guy, Gary . . . trailer roof . . . 
The bold part was meant to convey extreme distances where the trajectory becomes more relative, generally speaking. Who said anything about an Aim point? My scoped ARs on a rest hit the crow silhouette at 400 meters if I do my part. |
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Posted: 12/21/2014 9:18:17 PM EDT
[Last Edit: W_E_G]
[#13]
For the long shot "in the field," the slightly larger concern is probably going to be CANTING the rifle.
If the target might be shooting back, it may be difficult to get that "off a rest" shot with level sights. A 45-degree cant moves you about 2 inches at 100 yards. That's enough for you to probably miss your "crow." The biggest problems is always when the crow is shooting back, and also when the crow won't hold still. |
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Posted: 12/21/2014 11:34:06 PM EDT
[#14]
OK. The thread was about the affect of downhill shooting at a private range of 125 yds max. Your first post was correct-it's negligible. Now it's morphed into a live or die firefight.
Carry on. |
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Posted: 12/22/2014 10:21:56 AM EDT
[#15]
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Posted: 12/22/2014 7:27:24 PM EDT
[Last Edit: popnfresh]
[#16]
Your 60 feet at 125 yards is 9.2 degrees. So 100 yards at 9.2 degrees would be.. cos(9.2)= 0.987 x 100 yards would be 98.7 yards that gravity would be effecting the bullet. At 200yards it would be 197.4 yards actual horizontal range.
Of course you will be still shooting through 100 yards of atmosphere. None of that will matter but if you were shooting at 1000 or more you would want to adjust for it. |
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Posted: 12/23/2014 12:36:23 AM EDT
[Last Edit: Eric_75]
[#17]
Quote HistoryOriginally Posted By popnfresh:
... So 100 yards at 9.2 degrees would be.. cos(9.2)= 0.987 x 100 yards would be 98.7 yards that gravity would be effecting the bullet. Yes this is the correct approach to thinking about these types of problem. The gravity component of the flight path in this case is only .99 x the distance a laser reads. If you are using a map (or Googe Earth image) to calculate range, then you don't have to make any correction at all. Secondary effects such as velocity decay and shifting BC act on the actual flight distance rather than the horizontal distance, but for shots under 800 yards and less than 45 degrees it is a good approximation to lump them in together. Don't put a cosine indicator on your rifle. If you are really curious to measure the angle, tie a string with a weight to your protractor, or use a compass dial and guess. |
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Posted: 12/23/2014 12:40:23 AM EDT
[Last Edit: RDTCU]
[#18]
Quote HistoryOriginally Posted By vbfg135:
http://www.midwayusa.com/product/615767/badger-ordnance-angle-cosine-indicator-kit-with-generation-2-picatinny-style-mount-aluminum-matte Something like this will help you find the angle you are shooting. It will give you the cosine to figure out the true distance. The only other way to be sure is to use a range finder that corrects for the angle of decline. Should be an easy tool to use for experienced distance shooters, but takes a while to get the concept for some. |
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Posted: 12/23/2014 6:24:55 PM EDT
[#19]
Wow. I have a lot to learn about precision shooting judging by the quality of info received in this thread lol.
Cant thank you all enough for the insight. |
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Posted: 12/25/2014 10:58:35 AM EDT
[#20]
Something else about shooting angles some forget is that even though your corrected range is shorter than actual range due to the angle, you still need to use the wind call for the actual range as the wind is effecting the bullet for that entire range. So if you were shooting downhill at 600 yards and with the angle it came out to say 500 yards you would use the elevation data for 500 yards but the wind data for 600 yards.
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Posted: 12/29/2014 10:58:36 PM EDT
[#21]
Quote HistoryOriginally Posted By Eric_75:
Yes this is the correct approach to thinking about these types of problem. The gravity component of the flight path in this case is only .99 x the distance a laser reads. If you are using a map (or Googe Earth image) to calculate range, then you don't have to make any correction at all. Don't put a cosine indicator on your rifle. If you are really curious to measure the angle, tie a string with a weight to your protractor, or use a compass dial and guess. Quote HistoryOriginally Posted By Eric_75:
Originally Posted By popnfresh:
... So 100 yards at 9.2 degrees would be.. cos(9.2)= 0.987 x 100 yards would be 98.7 yards that gravity would be effecting the bullet. Yes this is the correct approach to thinking about these types of problem. The gravity component of the flight path in this case is only .99 x the distance a laser reads. If you are using a map (or Googe Earth image) to calculate range, then you don't have to make any correction at all. Don't put a cosine indicator on your rifle. If you are really curious to measure the angle, tie a string with a weight to your protractor, or use a compass dial and guess. Yep you can get a protractor for about a dollar, tape a "sighting straw" to its back if you want to get real fancy. Or sight down your phone with the bubble level.I have Clinometer on my phone, I can sight down its length and it will lock on the angle. |
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Posted: 12/30/2014 8:31:19 AM EDT
[#22]
Or if you have a Mildot Master, which is a great piece of gear to have in the first place, it has one on the back and you just tie a weighted string to the corner. Then on the front they also have angle adjustments so no math is needed unless you want to do it.
http://www.mildotmaster.com/testdrive.htm |
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Posted: 1/21/2015 12:41:29 AM EDT
[#23]
The math is really quite easy if you want a specific answer, so is the science behind it, (projectile motion) physics 101. but the rule to remeber is whenever you shoot either up or downhill, you always aim low (poi will be high)
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