Down hill shot question

[lionhunter]

Thanks to those who had some insight to my question... Way to technical for me. At any rate; I was shooting a .270 wsm with a 130 gr accu-bond at 3248-3255 fps. b/c is .435. I have the b/c cross hairs in my scope. 300 hits dead nuts 4oo hits maybe an inch high. The "hypothetical" situations was a I glassed a pretty good buck at 347 yards, he was moving away from me towards a very thick flat. If he walked another 30 yards he would be gone fore good. the shot was an extreme down hill shot. By the time I got set up to take the shot I figured he was closer to 400 yard, (a shot I practice a ton, but in a flat area), I settle the 400 cross hair, and shot high. Not much high, but a miss is a miss.

 

O well, thanks again for the info.

Whitey

[308Nut]

Time for more popcorn!

 

 

In all honesty allow a guy to use a poor choice of words. Some experts have said things like 'the vacume of outer space'. Maybe I was a bit out of line thinking members here would understand what I meant.

[Ernesto C]

I'm not an expert but in the scenario you described at the begining I will aim dead on with my 257 WBY MAG.

 

Now another thing that a lot of people does not see is that when you are looking at a buck down hill you are not seeing one side of the buck only (assuming he's broadside) you are also seeing the opposite side of the buck! So if you aim dead center you are actually aiming at the opposite side of the buck and if in top of that you try to compensate for distance/bullet drop guess what? You are shooting high!

I have seen lots of people miss this type of shots, they are not easy but practice makes perfect. My two cents............Thank You.

 

Ernesto C

[rclouse79]

So you meant no gravity. . . . honest mistake.

 

308 quote:

"Why is this? Because all of the variables were not included. If bullets were fired in a vacume, simply multiplying the distance by the cosine would work flawlessly."

 

For arguments sake: If you were floating in the vacuum of space shooting your .308 at astro deer would you actually go to the trouble of ranging the distance and then mulltiply that by the cosine of some angle before shooting?

 

Before you knock my question remember it was the theoretical situation you tried to set up in your explanation.

[pwrguy]

Time for more popcorn!

 

 

In all honesty allow a guy to use a poor choice of words. Some experts have said things like 'the vacume of outer space'. Maybe I was a bit out of line thinking members here would understand what I meant.

 

Mike, I thought you knew about gravity, I can't believe I trusted you to set up my shot last December

[308Nut]

Time for more popcorn!

 

 

In all honesty allow a guy to use a poor choice of words. Some experts have said things like 'the vacume of outer space'. Maybe I was a bit out of line thinking members here would understand what I meant.

 

Mike, I thought you knew about gravity, I can't believe I trusted you to set up my shot last December

 

Yeah. I bet you will never make that mistake again!!

 

In all fairness, I can step up to the plate and admit that I used a poor choice of words. If you want to nit pick and find fault with what I said that is your right. That said, if any of you want to get into a debate on the ins and outs of shooting up or down a slope in the real world, in a vacume with or with out gravity or whathaveyou.....I am game for it for as long as you can sit there and take it.

 

M

[rclouse79]

Ok I am done. . . . . felt a little ornery today. I guess not everybody enjoys my physics ramblings as much as I do.

[308Nut]

Thanks to those who had some insight to my question... Way to technical for me. At any rate; I was shooting a .270 wsm with a 130 gr accu-bond at 3248-3255 fps. b/c is .435. I have the b/c cross hairs in my scope. 300 hits dead nuts 4oo hits maybe an inch high. The "hypothetical" situations was a I glassed a pretty good buck at 347 yards, he was moving away from me towards a very thick flat. If he walked another 30 yards he would be gone fore good. the shot was an extreme down hill shot. By the time I got set up to take the shot I figured he was closer to 400 yard, (a shot I practice a ton, but in a flat area), I settle the 400 cross hair, and shot high. Not much high, but a miss is a miss.

 

O well, thanks again for the info.

Whitey

 

Do you have an idea of what the angle was? Altitude? Temp?

 

It looks like for you to have shot over his back at 400 yards, the angle was most likely 35-40 degrees. Less degrees if you were aiming for 400 yards and he was actually closer to 380 yards. In any event, using the riflemans method at 350-400 yards between 30-40 degrees would have helped tremendously.

 

There is NO shame in missing SO LONG as you learn from it. If you never repeat this mistake than it was worth it.

 

M

[308Nut]

rclouse79,

 

You dont have to exit. You pointed out a very valid flaw in my explanation. Yes I understand the physics behind it, no I did not explain it properly. It was late and I was tired, my 21 month old daughter was tugging on me etc......

 

You're absolutly right about the straight line in a vacume with no gravity. There would be no need for correction regardless of any angles as there is no trajectory. Homestly I have no idea what I was thinking when I said it. What was said was said and it doesnt add up so to speak. I can live with that. So allow me to correct myself.

 

In a vacume, (with gravity) the trajectories regardless of caliber, velocity, BC, etc...will all have the exact same center. Meaning that even though the maximum height of each trajectory is different, the highest point in each trajectory is exactally 1/2 way between the bullet's starting point and the ending point. In other words, the trajectories are purely parabolic. With this fact, in a vacume, the math involved is as simple as multiplying the cosine of the angle by the line of sight distance. With air density, the maximum height of the typical bullet trajectory is between the 1/2 way mark and the target AND will be different for each trajectory. In other words, the trajectories are not purely parabolic. It is because of air density that it becomes more complicated than just multiplying the cosine value by the line of sight distance. That is really the message and principal that I was trying to get accross.

 

Thank you for pointing that out.

 

For the record, you are 100% correct.

 

Now somthing else to chew....................

 

Lets say we were in a vacume (with gravity). The shot is 950 yards with a 40 degree slope. If you take 950 and multiply it by .766 for a corrected yardage of 728 yards, making the shot as simple as finding and using your 728 yard Mil or MOA hold over?

[rclouse79]

No worries. I understand you have a lot of practical shooting knowledge. I understand the part of your post I discussed was not relevant to most of the readers. Most people were more interested only in the information on how to compensate for different shots which you provided.

 

Now for the fun part!

 

If I knew the velocity of the gun I would multiply by the cos(40) to find the horizontal component of the velocity, and by the sin(40) to find the initial negative (downward) vertical velocity of the gun.

Since there is no air resistance there are no horizontal forces which means the horizontal component of the bullet will be constant until it hits the target. I would use the equation t=d/v where d is the distance to the target and v is the horizontal component of velocity. This will tell you time it takes for the bullet to reach the target.

During the time it takes the bullet to reach the target it is accelerating downward at (negative) 9.81 m/ss. Its downward displacement would be given according to the equation d = 1/2gtt + vt where g is acceleration due to gravity, t is the time to reach the target and v is the initial vertical component of the velocity.

 

After you know how far it will drop you could compare that to the drop distance of your scope.

 

This of course assumes that the bullet leaves the gun 40 degrees below the horizontal. If the target was 40 degrees below the horizontal the bullet would actually leave the gun at slightly less than 40 degrees since hunting rifles are sighted for a 100 or 200 yd zero.

[coues hunter]

If you are looking for the simple solution just pick up any of the angle compensating rangefinders out there. They will give you the exact horizontal shooting distance with zero guess work. I've been using the Nikon rifleman 550 for three years and it has worked flawlessly. They wont work at 950 but in all seriousness who really needs to take shots at that distance.

[Browning'sCustomMeat]

I believe Chuck Norris has something to do with bullet drop....AND gravity....

[rclouse79]

When Chuck Norris does a pushup he does not push himself up, he pushes the world down.

[CouesWhitetail]

When Chuck Norris does a pushup he does not push himself up, he pushes the world down.

 

 

LOL!!

[rclouse79]

If you are looking for the simple solution just pick up any of the angle compensating rangefinders out there. They will give you the exact horizontal shooting distance with zero guess work. I've been using the Nikon rifleman 550 for three years and it has worked flawlessly. They wont work at 950 but in all seriousness who really needs to take shots at that distance.

 

What fun is that? I will probably buy one of those for my next range finder.