Arrgh!!

wabi · Post by **wabi** » Wed Oct 21, 2009 9:36 pm

I've been having a problem with my crossbow suddenly (and unpredictably) shifting POI. I can sight in at 25 yards then a few days or even weeks later it will suddenly jump 2 - 3" high at 25 yards.
In the process of trying new rings (have them ordered) first to see if that helps.

Lone Wolf · Post by **Lone Wolf** » Wed Oct 21, 2009 9:38 pm

wabi wrote:I've been having a problem with my crossbow suddenly (and unpredictably) shifting POI. I can sight in at 25 yards then a few days or even weeks later it will suddenly jump 2 - 3" high at 25 yards.
In the process of trying new rings (have them ordered) first to see if that helps.

Hmm Ill have to check mine but after I got back I shot at 20 on the ground and it was fine.

peter p · Post by **peter p** » Wed Oct 21, 2009 9:47 pm

Always aim for the top of the heart, that way if it ducks the arrow it will still hit the lungs.
If it's a close shot like yours and you aimed for the top of the heart you would of had a dead deer. The arrow would have hit dead center on the deers chest.

Lone Wolf · Post by **Lone Wolf** » Wed Oct 21, 2009 9:50 pm

peter p wrote:Always aim for the top of the heart, that way if it ducks the arrow it will still hit the lungs.
If it's a close shot like yours and you aimed for the top of the heart you would of had a dead deer. The arrow would have hit dead center on the deers chest.

yep..that was my only mistake. If I would have went for the heart with the 20 yard marker that would have placed the 10 yard marker dead center. Im just glad I missed completely instead of making a bad shot

IAMCANADIAN · Post by **IAMCANADIAN** » Wed Oct 21, 2009 9:56 pm

Cossack wrote:Height has nothing to do with trajectory! It's the horizontal distance from the ground level base of the stand to the target that matters. Gravity acts on the arrow over that distance no matter how high you are up. This is not to say that height doesn't affect the angle at which the arrow penetrates the target, however. But aiming high or low to compensate for height is plain BS.

***sigh**** this again.

Angle DOES affect trajectory, it is NOT ..."BS".

Look at the post on rangefinders on page two...I explained it fully.

Gravity is a constant, however, the effect of gravity on an object such as an arrow is applied at a different time on an arrow that is fired on an angle, either up or down.

Bowster · Post by **Bowster** » Wed Oct 21, 2009 10:53 pm

I'm no algebra wiz but have been playing around with the pythagorean theorem which is basically the equation used to calculate the side of a triangle.

Was trying to see if one of the new range finders was worth the money for archery.

Here is what I figured out for a stand 15 feet up a tree:

Line of Sight distance: 15 yards - horizontal distance: 14 yards
Line of Sight distance: 20 yards - horizontal distance: 19.4 yards
Line of Sight distance: 25 yards - horizontal distance: 24.5 yards
Line of Sight distance: 30 yards - horizontal distance: 29.6 yards

and at 20 feet:
Line of Sight distance: 15 yards - horizontal distance: 13.4 yards
Line of Sight distance: 20 yards - horizontal distance: 18.9 yards
Line of Sight distance: 25 yards - horizontal distance: 24.1 yards
Line of Sight distance: 30 yards - horizontal distance: 29.2 yards

From this, I don't see the angle much of a factor in bow hunting situations.

Let me know if these don't sound right......

one shot scott · Post by **one shot scott** » Wed Oct 21, 2009 11:10 pm

I may sound stupid here, but did you sight in with broadheads? In my experiences every broad head flys much different than feildtips. (never used mechanicals) so that may be a different story.

IAMCANADIAN · Post by **IAMCANADIAN** » Thu Oct 22, 2009 6:56 am

Again, it's fully explained in the rangefinder thread, but in a nutshell:

The distance from the tree/stand makes very little difference , this is as you demonstrated with your figures comparison.

*However*, the pythagorean theorem which you are applying only takes into account distances, where A.R.C. (the program that the RF's use) takes into account the actual changes imparted on trajectory by the arrow being shot on an angle.

Your bow is sighted on level ground, therefore the arrow travels in a predictable arc, and is sighted in to match THAT arc (1.5" low at the stirrup, 3" high at 10, dead on at 20, etc. etc.)

However, when an arrow is shot an an angle (either up or down), gravity affects the arrow very differently, and the level-ground trajectory arc that you sighted in with goes out the window.

In it's simplest form, lets say you shot an arrow straight up....the arow goes up, flips, and comes down right? In this case your yardage markers mean nothing, as the arrow is not following your predetermined arc...ie: If you had a ballon at 10yards and a balloon at 50 yards up, you would use the same yardage marker for both (if you used the 50 yard pin, you would shoot well away from the ballon, as there has been no gravity pulling the arrow down like it does when horizontal)

The big question is WHY the trajectory is non existant when shot straight up, and the answer is because gravity has no affect on a vertical arrow, other than to slow it down and eventually stop it and bring it back down.
Gravity doesn't change the direction of the arrow until it has overcome the upward travel. The same applies if you shoot an arrow straight down....it doesn't travel in an arc, regardless of how high you are....an arrow shot straight down will travel in a straight line. Again, why? Because the gravity is applying the force to the arrow, but because the arrow isn't travelling horizontally the only effect it can have is to pull it straight down.

The same applies to an arrow shot on an angle, the amount of gravity applied to that arrow (or more accurately, the amount of time gravity has to affect the arrow) changes dependant on the angle shot.

The best thing a hunter can do is to actually practice with their bow from an elevated position to learn the trajectory differences that come from shooting down.

Lone Wolf · Post by **Lone Wolf** » Thu Oct 22, 2009 7:53 am

one shot scott wrote:I may sound stupid here, but did you sight in with broadheads? In my experiences every broad head flys much different than feildtips. (never used mechanicals) so that may be a different story.

Yes Sir.

Lone Wolf · Post by **Lone Wolf** » Thu Oct 22, 2009 10:03 am

First just want to thank everyone for the help.
Went out today determined to figure out what happened. What I found was 2 things. My 20 yard marker is about 1 1/2" high at 15 yards. The 10 yard marker is dead on. My first test shot revealed what I think my problem was. When I shot, I missed the target completely because I wasnt holding the forearm of the xbow tight enough and it jumped up a little..I think this plus the fact I was alreay 1 1/2" high caused me to over shoot. When I shot again, I held the forearm tight so it wouldnt move and using the 10 yard marker hit dead center..same with the 20 except 1 1/2" high..Since all my stands are fixed and 95% of my shots are 15 yards I will either use the 10 yard marker or re-sight the main marker at 15.

Mike P · Post by **Mike P** » Thu Oct 22, 2009 10:45 am

I'm going to need awshucks to explain this to me in language I can understand.

Nobody told me there would be math problems to do here!

All I know is this.

When I put the crosshairs on the bullseye at twenty-five yards and pull the trigger on either of my two excaliburs I hit the bullseye. When I go up in my climber twenty feet and shoot at the target from twenty-five yards I hit the bullseye. I sighted in at twenty-five originally.

As my comfort zone is thirty yards I just hold the crosshairs a smidge high at that distance, and, wait for it, I hit the bullseye. At ten yards I just hold a smidge low and, you guessed it, I hit the bullseye.

I do not mess with the little chevrons below the crosshairs of my varizones, I only use the crosshairs and move up a smidge or down a smidge. I find I seldom have time to calculate distances and determine what to use if not the crosshairs.

But hey, I am old and I was a marketing major. Math was never my strong suit.

So far, my system seems to work for me pretty well.

vaguru · Post by **vaguru** » Thu Oct 22, 2009 1:03 pm

IAM CANADIAN and I had a good dialogue in the other thread he mentioned. Almost had me convinced too! Talked to some of my buddies who have hunted out of tree stands for years, some with the xbow. Their responses all indicated regardless of stand height, shoot for level ground yardage. As I haven't had the opportunity to practice out of my NEW climber, or from the roof of the house, I took their word for it. I shot my first buck out of that stand Tuesday evening (story to come later). I aimed for the lasered distance to the spot, less 1 yd for difference of level to height, and had perfect height impact. Now I was 18' up in the tree, and the base of my tree is near 10' above the trail the buck was on. So....I agree with MikeP and Cossack. If there is any other heigth to the shot, it must be something else, a form issue or parallax. I know it's only one shot for me, but others have many. To those of you using different aiming methods, if they work for you great. JMHO.

Mike P · Post by **Mike P** » Thu Oct 22, 2009 1:29 pm

bstout wrote:Mike, you're not dealing with much of an angle with a shooting distance of 25 yards or more, especially if you're hunting over level terrain.

No offense, Mike but many flat landers don't have to deal with this very often or at least not to the same extent as hill folks.

There's very little level ground around here that doesn't have crops growing on it. Almost all of our woods are located in extremely uneven, non-tillable terrain. We get some nasty steep downward shots into deep ravines.

OK, I was a flat lander when I lived in Northern Illinois, I admit that. Every time I went hunting or fishing up around Eagle River all you cheesheads would call me that, lol.

I was even more of a flat lander when I lived in Kansas. It was like a billiard table.

But I grew up in the "Hill Country" of Texas and we sure had some ups and downs.

Where I live now bstout is very hilly. The glaciers really did a number here in southwestern Ohio. I hunt very little level ground. Level ground here is also utilized for crop fields just like where you are. You might say I am in the foothills of the Appalachian Mountains. Our hollows around here run deep and steep.

Now that that's out of the way, here is what I think.

I do not shoot beyond thirty yards. I don't think there is much of an issue of hold low or hold high within that range regardless of the terrain. If there is, I am not a good enough shot that it matters as I think the difference either high or low is small enough that my poor shooting is more of a concern then the trigonometry of the shot.

I think the answer to this entire discussion is to shoot short distances. So that's my story and I am stickin to it.

That is until awshucks weighs in and splains it to me.

He can really cipher.

Mike P · Post by **Mike P** » Thu Oct 22, 2009 3:37 pm

bstout wrote: The age old problem of, "You can take a horse to water but...you can't drowned him!

Thats why I have an ATV.

You can shoot them.

Just ask shucks.

XCaddis · Post by **XCaddis** » Thu Oct 22, 2009 8:45 pm

awshucks wrote:
.settled the cross hair on the shoulder and shot...bolt sailed right over its back!
My guess, and it's just that, is you got 'string jumped.' Actually, 'string ducked' is more like it.

My experiences have led me to believe that from 10-20 yds, there's about 2" diff in poi, well w/in 'minute of deer' accuracy'

If the bow is shooting 300+ at 10 yards, I can't see the deer jumping the string...no way it is going to react fast enough....unless it was a coincidental movement

My 2 cents...