Scope Question

[newton]

Ok, not sure where to ask this question. But it will be used in the field for hunting so I am going to ask it here. I hope I get someone who understands me to chime in.

I have a scope. Its made by TC and its 3x9x40. It has a duplex reticle. What I am wanting to figure out is a way to estimate holdover for different ranges. My load is not a deciding factor in this at all.

I am going to check it out for sure tonight, but I believe that at 100 yards with the scope set on 9x the distance from the cross hairs to the point at which the thin line meets the thick line(there is a little arrow) is roughly 8".

So, does that mean at 200 yards it would be 16"? 300 yards 24"?

Also, is there a linear scale to figure what the distance would be if I dropped the magnification down to 6x? Would you take the field of view, which is roughly 15' at 9x and 45' at 3x, subtract the two(30' of difference between 9x and 3x), then divide that in half(midway between 3 and 9 is 6x) which would be 15', and add 15' to the 3x or subtract it from the 9x? So technically, I am asking, should the field of view be 30' at 6x power on the above scope with the above known field of views?

It sounds complicated, but I know its not. I only have 100 yards to test this out. I am using the scope on a muzzle-loader and want to be able to figure holdover for it.

For an example. Say my boolit drops 22" from zero at 200 yards. At 100 yards I am hitting midway between the cross hairs and where the duplex lines meet. If I measured this and it was 3" that would mean at 100 yards the distance between the cross hairs and the duplex is 6". So that would mean at 200 yards the distance would be 12", yes - no?

And then, throw the magnification thing in. Say I turn the scope to 6x, the half way point. Then as long as I know what the distance is, between the two points I am using, is at 3x I can do the same calculation as I would use for the field of view issue?

Confused yet? Hope not.

[newton]

Ok, so I did more looking. Guess what I am talking about is called sub-tension. I also guess that it is true what I am thinking as far as fixed power is concerned, and as far as magnification is concerned I'll just have to do some testing to find out.

Anyone ever done this kind of thing with their scopes?

[AggieEE]

I think you're trying to make things more complicated than they need to be. If you have 6" between cross hair and post at 9x @100yds you have a 6min. window, give or take a little 1" at 100yds is not 1 min of angle but close enough. At 6x the window will be 1.5 times bigger (1.5 x 6 = 9) and at 3x the window will be 3 times bigger. Knowing this you can make an educated guess at range if you think you know how big your target is. At 9x you can bracket a 18" deep chest of an animal then 6" divided into 18" gives you 3 so the target is 300 yards out. I hope this helps.
AggieEE

[newton]

Yep. That's what it is. I'm thinking it's actually 5 Moa. I tried it out and it's right around 5" at 100 yards. It's hard to tell any closer than that. But when I take it to 6x it bings it out to 8"(7.5 supposed to be), and then right around 15"-16" at 3x.

So it works rather well. It will be nice to know where to hold over at the longer shots. So if I am shooting 200 yards with my current setup I can hold my bottom duplex on the target and see where the top reticle sits. That then is my poa and I'll be a little over 20". Which is what I drop at 200.

I'll have to try out the range finding part of it sometime also.

[Wolfer]

I have used this method on my elk hunting rifle for years. If you know what you have @100 it can be exterpolated on out. But the only way to know for sure is to try it at said ranges and shoot it.

For instance, I painted two horizontal lines 30" apart on a big piece of cardboard. This was what I read to be the back to brisket measurement for a mature bull elk. I've since found most of the elk I see will go 24-26". Anyway at 400 yds I adjusted the power until the posts touched both lines. On my 3-9 leopold it read 7 power. So I knew if I carried my gun on 7 power and I threw it up on an elk and he more than filled the center he was closer than 400, if not he was farther away.

I then held the crosshairs on the back line and shot. I then paint the bullet hole and go back to the 400 yd mark. With the crosshairs on the back line I adjust the power until the post comes to the bullet hole. In my case it was once again 7 power.
I've done this with all the ranges out to 500 yds.
So I know that as long as I don't change my load and I have it lined up exactly 2" high @ 200 yds it will land 4" low @ 300 and on the post @ 7 power @ 400 and on the post @ 3-1/2 power @ 500

Ive since learned that with my scope I can bracket an elk @ 8 power for 400 and 9 power for 500
I used to keep a chart on the side of my gun but I used the same method for so many years that now I have it committed to memory.
Hope this helps.

[newton]

Yes. I was thinking the same thing about keeping it on my gun till I get it memorized. I am sure it would take a few years, but then it would be in my brain.

I tested it out last night. It is exactly 5 moa from cross hairs to duplex point. And the duplex point itself is 1 moa.

I have heard they made these standard sizes like that so they could be used in this manner. It also worked out just right when backing down the magnification. At 3x I was 15 moa on the nose.

Learn something new every day.

[runfiverun]

you know i have never had a deer or elk stand around long enough to fiddle around with my scope and get out a calculator.
i jst figured out a point blank range for over and under my cross hairs and hunted within those capabilities.
i turn down the scope in the timber and turn it p when looking across canyon.
if the animal is beyond just putting the cross hairs on center mass i get closer or pass on the shot.

i had to pass pulling the trigger on a very,very nice 4x4 mule deer because i couldn't reliably make the shot with the gun i was carrying.
it would have been a chip shot with one of my other rifles,but there is no way i would have been trying to size the animal up with power settings and stuff.

[helice]

Very interesting posts. I have work to do.

[Wolfer]

R5r
Your exactly right about most critters don't stand around long enough to fiddle with your scope, get out your range finder etc. that's why when I'm elk hunting in open country I carry my scope on 8 X. As soon as I look thru it I know which side of 400 he's on.
My scope covers 16" between the crosshairs and the duplex @ 400 so they will both fit on an elk at that range.
If they will hold for less than a minute I'll air mail them 210 gr of whup-***.

[Wolfer]

Seem like I read somewhere that all leopold scopes when set at their highest power will have 8" between the crosshairs and the duplex at 300 yds. This gives nearly all guns an aiming point at 300.
For instance let's say a 308 dead on at 100 will probably be around 10" low at 300. Close enough to use the duplex. A 300 win mag may only be 6" low at 300. Once again close enough to use. Most modern high power rifles will work with this system.

I'm doing a lot of guessing at these numbers guys.

[newton]

Yea, I doubt I'll use it to determine range. I have a range finder for that. But it's going to be nice to use as a holdover.

[NSP64]

Get a scope that has mil dot crosshairs and you will never go back. The guesswork is taken out and the mfg supplies a chart.

[atr]

I agree with runfiverun....I too have never had a deer or elk hang around long enough for me to screw around with the power magnification to estimate yardage. Estimating yardage (visually) beforehand to stands of trees or clumps of shrubs etc. is my method. Critters DO see movement and I try to minimize movement so as not to spook them