bullet drop conpensating scopes?
- Thread starter BOBTAILS
- Start date
kyotekiller25
Well-known member
They are usually calibrated at the highest magnification, or at 10x. Just depends. The manufacturer will know for sure. Call and ask them.
wildlife
New member
Not all are calibrated the same. An example is the Leupold VX-7 scope. You may need to use a lower magnification in order for your reticle to be accurate. So if your scope tops out at 14x you may neeed to use 7x in order to get an accurate bullet drop on the shot.
Every manufacturer is different and you should check them out prior to purchase so you get the model that suits your needs the best.
Every manufacturer is different and you should check them out prior to purchase so you get the model that suits your needs the best.
promapper
New member
BOBTAILS
Active member
I looked at both of my scopes, one is a nikon and the other is a pentax and neither of them said what they were calibrated for, so I usually shoot my rifles with the scopes on 6x, but today I went to the range and used 9x and then went back to 6x. So will this make my point of impact higher or lower? I am just not getting it on how changing the magification changes the point of impact.
kyotekiller25
Well-known member
Well what did your range results tell you??? Was it higher or lower???
I cant explain how or why magnification changes it, but I know it has something to do with spacing on the target. I think. I know FFP scopes dont have this problem, but there usually LR or military scopes, and are usually quite expensive.
I cant explain how or why magnification changes it, but I know it has something to do with spacing on the target. I think. I know FFP scopes dont have this problem, but there usually LR or military scopes, and are usually quite expensive.
The "spacing on the target" is what's referred to as "subtension." If u are using a first focal plane scope u will immediately know it as soon as u change the power. The reticle gets bigger and smaller as u change the power, but the subtension between any 2 points on the reticle stays the same. This means that if u are using the reticle for downrange zeroing (or rangefinding) the zeros will remain constant at any power. These scopes are uncommon since most hunters don't want their reticles to be harder to see when u lower the power.
That Pentax u have is surely calibrated for 9X. The next time u r at the range or really anywhere that u can look at something thru the scope, bracket a target of some sort between any 2 stadia lines @ 9X (u can do the same thing with your plex reticles also--they often make for the simplest of ballistic and rangefinding reticles). Now adjust the scope to about 4.5X, and u will see that the target occupies only 1/2 the spacing between whatever stadia u're using since the system is inversely proportional, i.e. as magnification DECREASES subtension INCREASES. So yes it does make a BIG difference what power u're using when using the optic for zeroing or rangefinding.
... now, welcome to "tactical" shooting (for lack of a better term). Understanding these concepts will open a world of optics applications that u may never knew existed. It's amazing what can be accomplished with reticles once the concepts are understood.
That Pentax u have is surely calibrated for 9X. The next time u r at the range or really anywhere that u can look at something thru the scope, bracket a target of some sort between any 2 stadia lines @ 9X (u can do the same thing with your plex reticles also--they often make for the simplest of ballistic and rangefinding reticles). Now adjust the scope to about 4.5X, and u will see that the target occupies only 1/2 the spacing between whatever stadia u're using since the system is inversely proportional, i.e. as magnification DECREASES subtension INCREASES. So yes it does make a BIG difference what power u're using when using the optic for zeroing or rangefinding.
... now, welcome to "tactical" shooting (for lack of a better term). Understanding these concepts will open a world of optics applications that u may never knew existed. It's amazing what can be accomplished with reticles once the concepts are understood.
CatShooter
New member
Quote:
On a variable power scope with the bdc reticles, if you change the power does it change the point of impact? or does it just make the target look closer, like on duplex scopes /ubbthreads/images/graemlins/confused1.gif?
It does not change the point of impact of the original zero. If it was zeroed at 100yds, that will not change.
But, the reference points on the reticle for other ranges will change their point of impact at different powers.
It you have a scope that follows your cartridge at 10x, and you turn it to a different power, the zero will stay the same, but all the other referance points will change.
As pointed out earlier, some scopes (with first focal plane reticles) do not have this problems... they have other problems /ubbthreads/images/graemlins/frown.gif
.
On a variable power scope with the bdc reticles, if you change the power does it change the point of impact? or does it just make the target look closer, like on duplex scopes /ubbthreads/images/graemlins/confused1.gif?
It does not change the point of impact of the original zero. If it was zeroed at 100yds, that will not change.
But, the reference points on the reticle for other ranges will change their point of impact at different powers.
It you have a scope that follows your cartridge at 10x, and you turn it to a different power, the zero will stay the same, but all the other referance points will change.
As pointed out earlier, some scopes (with first focal plane reticles) do not have this problems... they have other problems /ubbthreads/images/graemlins/frown.gif
.
blinddog
New member
I had a old Refield 4-12 with BDC it did not matter what power you were on it was sighted in at 100 yards, the stadia lines told you what distace aproxamately the target was at, (depending on the size of the target) you then set the elivation knob to that range (with in 600 yards) and took the shot. POI was usually with in an inch or POA
If u zero the lower stadia at the optics highest power then as u lower the magnification the lower stadia zeros will climb higher on the target, since the stadia subtensions get larger.
Think about it, as u lower the power if your 2nd stadia is zeroed for say 400 yds. you're now increasing the distance between the stadia points and therefore aiming higher on your 400 yd. target.
Think about it, as u lower the power if your 2nd stadia is zeroed for say 400 yds. you're now increasing the distance between the stadia points and therefore aiming higher on your 400 yd. target.