A Conundrum...

8

'88Scrat

New member
Today I took out my little .17 HMR Savage to the range and bore witness to something that I cannot explain.

First off it is worth noteing that I have it sighted in @100 yards and am able to shoot a nickel sized pattern at that range with a Buress x16 power scope (yeah, I know its overkill for a .17 HMR).;) I was using Hornady 17 grain V-Max ammo.

After sending 50 rounds downrange at 100 yards I had some extra ammo so for grins I shot at a target at 25 yards.

I found that the rounds were actuall hitting about 1/2 an inch lower at 25 yards. Now I know that the trajectory of a .17 is negligable at 100 yards but still shouldn't the rounds be hitting higher? The only explanation I could come up with was that scope height was different enough to throw off the reticle.

Any other possibilities I'm not seeing?
 
oneoldsap said:
Your bullets are striking the target before they reach your line of sight / with a 100 yd. zero .
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Correct!

Your bore is angled upward for a 100yd zero, not level with the ground. There are two zeros, a short range and a long range. The bullet travels in an arc, intersecting the target zero as it is falling.

If it helps, think of throwing a football or a baseball to someone 50yds away. You can't throw it straight at them, it would hit the ground somewhere between you. Your brain calculates the angle needed when you throw. Halfway between you, the ball is over both your heads, correct? It then falls enough to intersect the person you are throwing the ball to at the correct distance. This is the way firearms work as well.

Just a long winded way of saying what oneoldsap said.
 
If you think of throwing the football underhanded it's easier to visualize the ball having to come up to eye level after it leaves your hand.
 
Here is a ballistic chart for your .17 HMR with VMAX @ 2550 fps.

17HMR.jpg


Because the line of bore is about 1.5" below the line of sight when the bullet starts out, it has to cross the line of sight twice, at 50 and then again at 100 yds., for a 100 yd. zero. It's about a 1/4" high at 75 yds. in between. But at 25 yds. it's still below the line of sight a little over 1/2".
 
Strangelove explained it very well, and the chart illustrates it perfectly.

are you fairly new to shooting? Get a few books. Not magazines, books. You need to learn some of the more essential things about shooting that nobody has taken the time to teach you, you won't find in magazines, and can't usually be figured out on your own, no matter how smart or clever you are.

Don't take that personally. The reason I suggest it is that this question is really, truly, one for a neophyte.
 
Originally posted by briandg
are you fairly new to shooting?
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Kinda yes kinda no. For the most part I grew up around shotguns (I live in Kansas and pheasant hunting is not a sport here its a way of life) so I know my scatter guns better than most. But while I know enough about rifles and pistols to appreciate and enjoy them but I don't shoot competitavly or anything.

That said, I'm always looking to learn more. You mentioned books, anything in particular you suggest?
 
science v. art

I've always sort of thought shotgunning was sort of an art form, that whole, lead, swing, follow through thing. Riflery as a science, velocity, energy ballistics.

There is a difference between line of sight. line of bore and the actual flight path of the bullet. The old ammo catalogs often had a nice picture of same.
 
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