Why do I have a lower impact point at closer range

[fabsroman]

I went to the indoor shooting range this weekend and played around with my 10/22.

The longest range there was 75 feet (i.e., 25 yards), which really wasn't much, but it was okay for playing around. Initially, the gun was shooting low at 25 yards, so I adjusted the scope upward and it was dead on. I was shooting quarter size groups at 25 yards and I was pretty happy, because the accuracy of this gun has been pretty miserable over the last couple of years. The lower impact point at 25 yards might have been because I was using CCI Mini's instead of the Stingers that I had initially used to site the gun in.

Now, on to the main question. I brought the target in to 10 yards (i.e., 30 feet), and while the group was close to dime sized for 10 rounds, they were all an ince lower than where I was aiming. Initially, I thought it might have been because I brought the scope down from 9 power to 3 power, so I went ahead and shot another group of 10 at 9 power and the shots were through the same hole (i.e., an inch lower than where I was aiming.

How can a scoped gun be dead on at 25 yards, and low at 10 yards. I was trying to run this scenario through my mind and I cannot figure it out I understand that a bullet starts to fall as soon as it leaves the muzzle, such that there are two spots where it is dead on with the crosshairs. In other words, the scope is sighted in for line of sight which is a straight line but the bullet's path is sort of a parabala.

Can anybody help me figure out the answer so I don't lose too much more sleep?

[TreeDoc]

You answered your own question, Fabs! It's the trajectory of the bullet. Typical line of site is 1.5" higher than the bore so the bullet leaves the gun 1.5" low. The line of the bore is canted upward in relation to the line of site. The bullet eventually crosses the line of site and climbs above it and reaches an apex of it path and starts downward and eventually crosses the line of site again.

If you were to hold your paper against the muzzle and line the crosshairs dead nuts center of the target it would be 1.5" low then as you move the paper away from the muzzle the POI would steadily climb.

I think I'm understanding your question and your statement is spot on.

[Dom]

Don't lose no sleep Fabs, I think it's because line of sight thru the scope is higher than looking thru the barrel, so the bullet is rising to be on at whatever range you dialed the scope in for. I'd think you could dial the scope in for the 30 feet and it'd be high at 75 feet -- I'd be surprised if it wasn't. Anyway, I agree, it's all trajectory and line of sight, Waidmannsheil, Dom.

[fabsroman]

I thought about it some more after writing the post and I think you are dead on TD.

In essence, the bullet would start out lower then the scope, cross the line of sight at 25 yards (hence dead on at 25 yards) and the cross the line of sight again further down range at say approximately 75 yards since the gun was initially sighted in for 50 yards and I had to raise the scope to get on at 25 yards.

In essence, 25 yards was the intial zero with some other further yardage being the final zero.I just drew myself a diagram and it really makes sense now. I am just not used to shooting a rifle at 10 yards since most of my rifle work is done in the open field at 100+ yards.

Thanks TD

[Hawkeye6]

Fabs:

If you look at a ballistic chart for any rifle/load you'll find that to be exactly the case. The expected impact point for your sighted-in range will be 0". At ranges shorter to that, the expected impact point will be lower. At longer ranges it will increase to a certain max. Then decrease again through a second "zero" and drop rapidly.

A really important consideration in setting your "zero" point is the effect it has on your "point-blank" range. Porbably not a really big consideration for a .22LR like the 10/22, but if you are using a laaarger calibler rifle for deer or other large game hunting.

H.

[Gotcha!]

Fabs,

You would have had a coronary if you had been shooting one of the "competition" guns guys are shooting with the scope mounted 10-12" above the bore! I saw that on one of the "outdoor shows" and wondered why they would do that?

[fabsroman]

Why do they do that? Is it so they can angle the scope downward to better match the long range trajectory of the bullet? Honestly, I have no idea why anybody would mount a scope a foot over the bore.

[Gotcha!]

I think it has to do with being able to stand with their heads erect and necks straight. Must be something to it or so many wouldn't be doing it.

[Rocky Raab]

Those foot-high mounts are on Contender or other pistols - and they allow the shooter to hold the gun about mid-chest with both hands. That's a very steady position, but normal mounts would make it impossible to see through the scope, so...

On the other question, the repliers said it perfectly. And I'm sure Fabs has it straight now. BTW, the higher the mounts, the more exaggerated the close in low hits get.

If the scope (or any other sight) were somehow BELOW or LEVEL with the bore, the bullet would cross the line of sight only once.