## Thursday, November 01, 2007

### How to shoot at elevated targets

by B.B. Pelletier

This one is for the man who asked me last week how to hold for a target that is up in a tree or that was lower than the shooter. I did direct him to the post where that was discussed, but he needed to see a picture, so here it goes.

Up a tree: How to hold for shots that aren't on the level
When shooting at targets that are above or below you, estimate the distance to the target as though it was on the level with you. If you were shooting at a rat from a third-story attic window, the rat might only be five feet from you, if it were on your level. The fact that it is actually 40 feet away makes no difference. Only the distance to the rat on the same level counts, because that is all the distance that gravity has to act.

Let's turn that around. What if a squirrel is 50 feet directly above you in a tree? There is no linear distance. If you were on his level, one of you would be standing on the other. You will be shooting straight up, and the pellet will have no chance to be affected by gravity, except that it will act to slow the pellet in flight. For this shot, your pellet will strike the target as far below the aim point as the center of the scope is above the bore. It's the same as shooting at a target that's touching the muzzle of the gun.

To determine the proper holdover for an elevated or depressed target, determine the distance if the target were on your level. In this case, the distance to the base of the tree.

Not exact, but close enough
This method of determination is not exact, but it's close enough for hunters. Because the slant range is longer for an elevated or depressed target, the flight time is also longer, so there is actually a miniscule amount of extra drop compared to a shot taken on the level at the same distance. When you are shooting at Army tanks on a hill three miles away, it matters. For squirrels at 50 yards, it doesn't. Slant range is the longer length of the hypotenuse of a right triangle compared to the vertical leg.

You might wonder what happens when you shoot straight up or down. Well, gravity does act to either speed up or slow down the pellet, but not to move it off the straight line it travels. However, the difficulty of shooting EXACTLY straight up or down almost guarantees that the shot will be pulled off course a little.

At November 01, 2007 6:29 AM,  JP said...

Good advice for hunters. I've had a few questions about this myself. I've been previously "playing by ear" on these things, but now I've something to help work out a full understanding on. Thanks. JP

At November 01, 2007 7:24 AM,  Anonymous said...

You mentioned a previous post with this subject. Could you get us a link to it? Anon

At November 01, 2007 8:43 AM,  Anonymous said...

WHOA! How fast is terminal velocity? I thought it was somewhere around 120 M.P.H.? Would you convert 1000 F.P.S. to M.P.H. Reason for my question is you said gravity would speed up a pellet if shot straight down. I assumed 1000 F.P.S. was/is faster then terminal velocity? From savagesam

At November 01, 2007 8:58 AM,  Anonymous said...

Just did a google on terminal velocity. Boy was I wrong! only got one part right. Looking forward to that conversion. From savagesam

At November 01, 2007 9:20 AM,  Anonymous said...

A recent forum post said the newer two-tube 909 has more power than the single-tube 909s due to a new valve. Are there differences between older and newer versions of the two-tube 909? If so, what are they, and how can you tell the versions apart?

Thanks

Tedd

At November 01, 2007 9:25 AM,  J.R. said...

14 in Fla
SORRY I took up soooo much space in yesterdays comments with such a "STUPID" question. I thought the point of B.B.'s BLOG was to educate ALL airgunners, not just you "pros". Oh well C'EST LA VIE
J.R. in Ca

At November 01, 2007 9:41 AM,  J.R. said...

.22 multi-shot
Thanks so much for your incredible responses yesterday. Iwill be modifying both guns from your info alone, and I'm sure they'll turn out GREAT.
B.B.-hope you continue with this blog for many years, but if you should decide to retire (lol-I'm older than you)I NOMINATE .22 MULTI-SHOT!!!

At November 01, 2007 9:51 AM,  Anonymous said...

B.B.
Thanks for the explanation. This is very clear.

For the question about terminal velocity, my understanding is that it has to do with the cross-section of whatever is falling and 120mph applies only to human bodies in free fall

Matt

At November 01, 2007 10:35 AM,  Joe in MD said...

BB,

You have reproduced the "Rifleman's Rule" which has been supplanted by the "Rifleman's Improved Rule". Neither are usable for airgunners at typical ranges.

I propose the "Airgunner's Rule" -- If the target is closer than 20 yards or at less than 20 degrees deflection (either up or down), just shoot at the center of the kill zone. Otherwise, shoot at the bottom of the kill zone.

This is based on the following hold under table I computed for my 18fpe gun but works pretty well for most airguns:

Hold Unders for Angled Shots
Range/Deg,10,20,30,40
(Yard),(Inch),(Inch),(Inch),(Inch)

10,0.00,0.01,0.03,0.05
15,-0.36,0.03,0.07,0.12
20,0.01,0.06,0.12,0.10
25,0.03,0.10,0.20,0.47
30,0.03,0.13,0.28,0.50
35,0.05,0.18,0.39,0.69
40,0.06,0.23,0.52,0.90
45,0.08,0.30,0.66,1.16
50,0.09,0.37,0.83,1.45
55,0.12,0.46,1.02,1.78

(sorry, better formatting got lost).

Best,

Joe

At November 01, 2007 12:13 PM,  .22 multi-shot said...

One warning ... modding can be addictive. The following page has a lot of good links http://airgunartisans.com/. Here is another site with a list of mods http://crosmanmods.cjb.net/. Take a look, there is a lot of info out there!

Take a look at the following blogs by BB before you decide to get the LPA mim sight.
http://www.pyramydair.com/blog/2006/09/crosmans-2300t-part-1the-other-miracle.html
http://www.pyramydair.com/blog/2006/09/crosmans-2300t-part-2.html

.22 multi-shot

At November 01, 2007 1:49 PM,  Thomas L. said...

thanks, BB, that makes sense. Now I just need to practice and perfect my technique.

At November 01, 2007 2:23 PM,  Anonymous said...

I never intended for my comment about the coincidence of your questions with blog entries to offend...I just noted that you could try searching through the archives first, because B.B writes articles that explains the issues in much better detail(after all, this IS his blog, and he DOES professionally review airguns).

And incidently, I can't be a "pro" at airgunning. I don't(and still can't legally) own one yet. Just good at the facts. Based on your larger comment base, you're probably more aware of airguns and their attributes than me. I've only recently entered the interesting and disciplined world of air guns.

Rather embarrassed but still ready to help,

14 in Fla

At November 01, 2007 8:23 PM,  David N said...

I do't think your conclusion on effect of gravity is correct. Your projectile-path drawing of the tree tells why:

The effect of gravity, (X)is not a function of distance, but of time.
All things fall at the same rate. The drop, (X), is determined by the time in flight, which is determined by the velocity and the distance. A target high up the the tree is farther away - (it's the hypotenuse of the triangle) therefore the flight is farther, the time is longer, and the effect of gravity, (the drop, X), is greater.

At November 01, 2007 8:32 PM,  Anonymous said...

David N is correct.

The drop is determined by the time in the air and nothing else - all things fall at 32ft/sec/sec. There is nothing in the formula for distance. Assuming the pellet flys at constant velocity, it MUST be in the air longer to reach the target because it needs to fly farther.. A longer flight time means a greater drop. As the target gets farther away, you need to aim higher, it does not matter how the target gets farther away.

At November 01, 2007 10:07 PM,  pestbgone said...

David N and anonymous,
Re-read BBs blog, specifically the paragraph that says "not exact, but close enough." He talks about time of flight and how its effect is negligible in practical application. We are dealing with approximations here.
If you want to get exact like you are talking about, and calculate the time of flight and drop for the slant distance, the hold over must be reduced by multiplying it by the cosine of the angle of aim. This is because the bullet drops toward the center of the earth, not necessarily perpendicular to the line of travel. If you are shooting straight up, the angle is 90 degrees and the cosine is zero, therefor the holdover is zero, no matter what the TOF is. If the angle is 45 degrees, the cosine is .707, so you must reduce the holdover by 29% AS SEEN THRU THE SCOPE. At most angles, especially below 45 degrees, reducing the holdover by the cosine of the angle cancels out (approximately) the extra drop from the longer TOF. Like BB said, for squirrels at 50 yards, it doesn't matter.
Don't forget the scope height compensation, which BB also mentioned.
In real life airgun application, BBs method works.
Pestbgone

At November 01, 2007 10:53 PM,  Anonymous said...

In other words, when you angle up, gravity's pull is split between cancelling velocity and making the pellet drop. When you shoot level, gravity doesn't affect velocity, it just makes the pellet drop.

At November 02, 2007 2:08 AM,  Ozark said...

Savage - I think that pellet at 1000fps works out to 681 mph - much faster than terminal velocity. Actually, IIRC, even shooting it down is going to slow down, but then that all gets confusing and not helping matters at all.. I'll be quiet now.
Ozark

At November 02, 2007 5:28 AM,  Anonymous said...

Think I posted this link B4 but it's till relevent and may help some of you. Hope it helps.

http://www.snipertools.com/aci.htm

This is another great site for explaining several airgun and sighting concepts.

http://www.arld1.com/

happy shooting,
Turtle

At November 02, 2007 6:02 AM,  pestbgone said...

Turtle, anonymous, and all,
Thanks for the additional feedback and links. There are so many factors involved when shooting at an angle that the precise physics of external ballistics gets really complicated, and handy approximations keep it practical. I re-read my post and I guess, as they say, I really don't know what I don't know. Thanks for the new links and input, they are very helpful and its always good to listen and learn.
Pestbgone
P.S. My "airgun" bookmark folder is getting really packed with good stuff!

At November 02, 2007 9:10 AM,  B.B. Pelletier said...

David,

I did mention an insignificant variation in the impact point due to flight time variation. You are talking a difference of a few hundredths of an inch at 20-30 yards, so it's useless to think about it. The pellet 's natural dispersion is ten times larger.

B.B.

At November 02, 2007 9:14 AM,  B.B. Pelletier said...

Pellet drop,

You have it exactly right!

And on depressed shots you have accelleration and pellet drop combined.

B.B.

At November 02, 2007 4:31 PM,  Anonymous said...

A Pleasure Pestbgone.
turtle

At November 03, 2007 7:58 AM,  Mary Patrick said...

No need to be afraid of math..
For ease of demonstration, let's use BB's drawing, a tree 25yds away w/ a squirel 25yds up. 750fps average velocity.

Time in aloft if horizontal
=75ft / 750 = .1 sec. Drop = 1/2*32fps/s = 1.6in.
Hypotenuse = sq root of (25*25+25*25) = 35yds = 105ft.
Time aloft up in tree= 105/750=.14sec, drop = 2.24in.

The diference is an added .64 inches - enough to miss.

It gets much worse if the target is farther out or higher up, because the actualy velocity falls off fast and the time aloft increases - giving gravity more time to mess things up.

At November 04, 2007 9:03 PM,  Anonymous said...

Gravity is a constant and therefore can be factored in and dealt with. It doesn't mess anything up except my face and my joints as I get older... Air movement however, messes things up. I think we all should get outside (if possible) and put a target up in a tree, and one at the base of the tree, and find out definitively how it works.

I have to type the code in twice too.

/Shooter

At November 11, 2007 9:29 PM,  Mark said...

BB,
Looking for the rest of your series on tuning a spring gun.
http://www.pyramydair.com/blog/2006/07/spring-gun-tuning-part-5powerplant.html
Can you tell me where it is? I have searched Google and could not find.
Seems like the Google blog search is not very effective.

Mark

At November 12, 2007 5:57 AM,  B.B. Pelletier said...

Mark,

I typed in Spring gun tune in the search function window and the third hit was this:

http://www.pyramydair.com/blog/2006/08/spring-gun-tune-part-13-range-testing.html

Since that is the highest number of parts, Click on it and the links for the 12 earlier parts are at the beginning of the article.

B.B.

At November 12, 2007 6:31 PM,  Mark said...

BB, Thanks for the search help and just wondering based on your comments below:
The best of all
Talon and Talon SS owners who have the 24" optional barrel installed will get a HUGE adjustment spread! From 15 on the top end down to 4 or 5 on the bottom, they will have the greatest air rifle on the market - especially when you consider that just installing the standard tank will boost them to a maximum of 45 foot-pounds! There is nothing close to this performance spread anywhere else.

How can I buy a Talon or Talon SS with a 24" barrel stock and the air pump to pump it up?
ie. Buying a gun the way you want it ready to shoot.

Thanks, Mark

At November 12, 2007 6:39 PM,  royaltychimney said...

Could anyone tell me if you can shot the raptor pellet from the Benjamin pump riffle. Would it hurt the rifling. I would appreciate your help. Thank you

At November 13, 2007 6:07 AM,  B.B. Pelletier said...

Mark,

The Talon SS is only available with a 12-inch barrel standard. The 24-inch barrel is an option, only, on that gun. As for a hand pump, I do recommend that you get the AirForce pump. It's stronger than the FX design and built more robustly.

B.B.

At November 13, 2007 6:09 AM,  B.B. Pelletier said...

royaltychimney,

I have to say I believe the Raptor pellet is too hard to be shot safely in a Benjamin 397. The barrel is brass and the pellet is made from zinc.

B.B.

At November 13, 2007 6:46 AM,  Mark said...

Thanks BB,
I asked Air Force and they said:

At this time we do not offer custom built rifles. This may be an option at a later date however it could be a few months out.

You may check with some of our dealers listed on our website if they could possibly sell the rifle to you this way.

Thank you,
AirForce Airguns

So, I thought I would ask but that was when I thought you worked for Pyramyd, reading a post last night I discovered you did not.

I am thankful for all of your wisdom and willingness to put up with some of our stupid questions(I know there is "no stupid questions")but I am very thankful for kindness in that area.

On the SS with the mentioned pump, is there anything else I need to start shooting (besides pellets, scope, firing range)?

Thanks for the link on spinger tuning, I am going to take my RWS48 apart when I get home and try.

Last, on the 48 I have read everything I can find on shooting springers better (my group is between 1/2" and 2" at 20 yards) I am getting a scale and chrony. On the site picture after the shot, should the cross hairs always end up in the same place on the target. If so, I have some real practice to do on consistent holding.

Thanks Mark

At November 13, 2007 8:55 AM,  B.B. Pelletier said...

Mark,

After the shot with a springer the crosshairs seldom rest on the target. The gun moves with the shot. But relaxing and then seeing where the crosshairs are BEFORE the shot is very important.

B.B.