Help settle a debate

nicholal · #1 09-03-2008, 09:20 AM

Help settle this for me

A few of us guys were sitting around this morning at coffee break talking about our hunting rifles.

The conversation turned to sighting in a rifle. Some were saying they zero the rifle at short range at 3x power and 9x at longer range. (better to see target at longer ranges)

Now here is the debate

Some say the point of impact (poi) changes with diffrent scope powers.
IE. at 100 yards on 3x gun will hit dead on and at 9x it will be high.

I say there is no change as all that is changing is the magnafication of what you are looking at.

Never tried to prove or disprove this but I think it's straight forward common sense

AL

MountainTi · #2 09-03-2008, 09:29 AM

Yep, you're right, absolutely no change in POI when changing magnifications

sbtennex · #3 09-03-2008, 11:05 AM

There SHOULDN'T be a change in impact point - unfortunately that's not necessarily true. Try a $60 3-9 and you'll see what I mean. Quality scopes, generally true.

duffy4 · #4 09-03-2008, 02:03 PM

You are basically right Al, the change in magnification should not make any difference.

And for the record a rifle should not be sighted to be dead on at 100 yards. To get the best out of it.

Robin in Rocky

raised by wolves · #5 09-03-2008, 04:25 PM

Use the highest magnification possible when sighting in, even at the 100 metre range. It allows for more precise lateral adjustments.

A modern "quality" brand should not change the POI. Some of the first models of variable magnification scopes had trouble with a shifting POI. One of your buddies has probably heard a complaint about a scope from 20 years ago and simply reiterated it as truth. Some of the junky scopes; such as Tasco, still have difficulties with shifting POI.

nicholal · #6 09-03-2008, 04:36 PM

Quote:

Originally Posted by duffy4

You are basically right Al, the change in magnification should not make any difference.

And for the record a rifle should not be sighted to be dead on at 100 yards. To get the best out of it.

Robin in Rocky

Robin your correct
I was using that as a refferance. ......lol But I will take 3 shots in one hole bang on at a 100...if i could but cant

AL

dkrhome · #7 09-03-2008, 04:56 PM

Gravity does not affect line of site which is what a scope uses. I would say they are thinking about the gravity pull on a bullet that causes it to arc down.

Morbius131 · #8 09-03-2008, 05:53 PM

Hey Robin,

I don't agree or disagree with you concerning sighting a gun in at 100 yard but can you tell my why you say "to get the best out of a rifle it shouldn't be sighted in at 100 yards".

Morb

#9 09-03-2008, 06:30 PM

duffy wrote[QUOTE]And for the record a rifle should not be sighted to be dead on at 100 yards. To get the best out of it.

Quote:

/QUOTE]tell my why you say "to get the best out of a rifle it shouldn't be sighted in at 100 yards".

you know he didnt say it should be sighted in at 100 yrds you should re-read his post morb

there is a diff.

duffy4 · #10 09-03-2008, 06:36 PM

As soon as your bullet leaves the barrel gravity starts pulling it downward. That is why your scope or sights look right in the middle of the bull's eye but your barrel is pointed slightly up. So the bullet comes out of the barrel and gravity starts to pull it down but because the barrel is pointed up the bullet goes over the line of your sights a short ways from the barrel and then continues above it to some point out there before it starts to come back down and crosses the line of site again. Then it continues to get lower and lower than the line of sight.

If you sigh "dead on" at 100 yards then your bullet on its downward path is crossing the line of sight at 100 yards. And from there on it gets lower and lower.

If your gun were sighted to hit say, 2.5 inches high at 100 yards and it is doing so on its upward flight (instead of its downward flight) then it will continue to be high to a point out closer to 200 yards and then start it downward flight and cross the line of sight (and be "dead on") out some where around say, 250 yards. It will continue on the downward flight and be only 3 or 4 inches low at 300 yards.

Therefore when you are out hunting lets say deer, you can aim right in the middle of a deer chest (which is about a 15 inch circle) and your bullet will strike about 3 inches high of the middle or 4 inches low of the middle all the way out to 300 yards. (DEAD DEER)

Dead on at 100 yards you will be low at 200 and lower at 250 and way lower at 300 yards.

This is all concerning a fairly modern high velocity round. Someone shooting a ,44 rem mag. may want to be sighted "dead on" at 100 yards and never take a shot beyond 125 yards.

I have a .58 cal muzzleloader and for it to be on at 100 yards it is 7 inches high at 50 yards. If I aim in the middle of a deers 6 inch neck at 50 yards I will miss neck.

Morbius131 · #11 09-03-2008, 06:45 PM

Thanks for the response Duffy. That is basically what I thought but not in as much detail.

River_runner take you snide remarks and useless comments somewhere else!

Morb

Grizzly Adams · #12 09-03-2008, 07:54 PM

I'm going to throw a little fly into the ointment.

I would argue that we sight in at 100 yards because it is convenient. The actual sighted in distance should optimize the trajectory of the cartridge.
Grizz

Dick284 · #13 09-03-2008, 08:14 PM

When sighting in at so many inches high at 100yds we are attempting to get our maximum point blank range(MPBR) as far from us a practical.
It works this way. With the 15" vital zone on a deer like duffy discribed,(i prefer a 12" zone) you have 7.5or (6") inches either side of center.
Now we attempt to set up our sighting to acheive a midrange trajectory of no more than the repsctive 7.5 or 6 inches high, and then see where the projectile path will fall below point of aim by the same amount.
When the above conditions are met, we have acheived our MPBR. What ever that happens to work out to at 100yds is what you end up sighting in for. Just remember to go and see if indeed all the calculated numbers work in the real world.

I myself do it a bit different, looking for no higher than 3" high for a mid range ordinate,(habit of holding a bit high just incase) and somewhere around 6" low for a maximum ordinate.
Coincidentally for most of the big 4 or 5 popular calibers that does work out to roughly 2.5" high at 100yds.

As for sighting in, use your maximum magnification. Decent optics do not, and should not suffer from a POI change when the magnification is changed. At least 20 to 25yrs ago (maybe longer) Leupold used to advertise a 9 shot group, 3 shots at 3x, 3@6x, and 3@9x, So I guess thats when the shifting zero with magnification theory went out the window.

Jester · #14 09-03-2008, 09:43 PM

Quote:

Coincidentally for most of the big 4 or 5 popular calibers that does work out to roughly 2.5" high at 100yds.

Yup,been doing this for years with my old -06.

2.5" high at 100yds.

bang on at 200yds

3.5" low at 300yrds....which is the limit for me.I'm not as good as some of you long range shooters..

sbtennex · #15 09-04-2008, 09:05 AM

Quote:

Originally Posted by Jester

Yup,been doing this for years with my old -06.

2.5" high at 100yds.

bang on at 200yds

3.5" low at 300yrds....which is the limit for me.I'm not as good as some of you long range shooters..

Actually 2.5" hi @ 100 you'll be even higher @ 200 - not "bang on", but closer to 3+" high, "bang on" somewhere around 260, 270 yds, 3" or so low @ 300, around 15" low @ 400. Don't quote me - these are off the top of my noggin for around 2800 fps MV.

John Spartan · #16 09-04-2008, 10:22 AM

I have to agree with Dick284 - I sighted in with my variables at maximum magnification to ensure best accuracy with the different magnifications.

Jester · #17 09-04-2008, 10:10 PM

Quote:

Originally Posted by sbtennex

Actually 2.5" hi @ 100 you'll be even higher @ 200 - not "bang on", but closer to 3+" high, "bang on" somewhere around 260, 270 yds, 3" or so low @ 300, around 15" low @ 400. Don't quote me - these are off the top of my noggin for around 2800 fps MV.

I don't think so Tim..