calibrating a scope

declan1980

whats the best procedure for calibrating a scope for actual bullet drop against ballistic data given by a program like jbm?

Slug chucker

Hi
Firstly you'll need to fire your selected gun & round through a chronograph to determine the actual velocity of the bullet. Bullet manufacturers tend to tell fibs about the true speed of their bullets to give the shooter the impression that they go quicker and drop less over distance. Once this is done decide the point blank zero of your quarry (size of the vitals zone of your target). So say for example a .223 50 grain rem round travels @ 3300 fps muzzle velocity, if zeroed @ 200 yards it'll be -0.1 inches @ 100 yards and -2.6 inches @ 250 yards. So if your hunting a fox and usually take chest shots then it drop him without any adjustment out to 250 yards. But the main thing is knowing the true velocity of your bullet. I have found ballistic calculators fine to get you close but actually firing them in the field will give you your true moa clicks that you can rely upon time after time.
I haven’t factored wind, angle of the shot etc as that’s stuff you figure out as your going along.
I hope this helps,
Cheers
Slug Chucker

Tackleberrywho

declan1980 wrote: »

whats the best procedure for calibrating a scope for actual bullet drop against ballistic data given by a program like jbm?

Let me know how you get on, a fellow "boards.ie" member is selling me a ballistics calc.
I pulled off a personal best today, a bunny 457 yards!
Although I aimed head and hit him in the shoulders.

I want to improve on this and hope the calc will be of assistance

Vegeta

declan1980 wrote: »

whats the best procedure for calibrating a scope for actual bullet drop against ballistic data given by a program like jbm?

If you're not going down the point blank zero route AND don't have access to a chronograph I'd advise the following

Get the manufacturers data (ballistic coefficient and muzzle velocity) and put it into the calculator. Print the drop chart

Then go to the range with the chart and check the chart for accuracy. If it is slightly off then increase or decrease the muzzle velocity in the calculator until you get a decent match to bullet performance.

It might still be off by a click or 2 but you can fine tune as you shoot more and more.

That's a quick and easy way to go about it

declan1980

Tackleberrywho wrote: »

Let me know how you get on, a fellow "boards.ie" member is selling me a ballistics calc.
I pulled off a personal best today, a bunny 457 yards!
Although I aimed head and hit him in the shoulders.

I want to improve on this and hope the calc will be of assistance

jesus, that was some shot lad. was that with the 308 or the 223?

Tackleberrywho

declan1980 wrote: »

jesus, that was some shot lad. was that with the 308 or the 223?

.223, I'll post pics later on the photos thread.
I actually brought the camera to take a decent pic.
I have a couple of places where decent shots are offered at decent ranges. Rabbits don't often oblige though!

dwighet

Vegeta wrote: »

If you're not going down the point blank zero route AND don't have access to a chronograph I'd advise the following

Get the manufacturers data (ballistic coefficient and muzzle velocity) and put it into the calculator. Print the drop chart

Then go to the range with the chart and check the chart for accuracy. If it is slightly off then increase or decrease the muzzle velocity in the calculator until you get a decent match to bullet performance.

It might still be off by a click or 2 but you can fine tune as you shoot more and more.

That's a quick and easy way to go about it

Thats the method I used for my 300 winmag using nightforce ballistics program,which is exbal with a few extra features....
I had to increase the muzzle velocity by 80 fps to get the actual trajectory..
Most programs will need tweaking...It can be done by changing muzzle velocity or changing the BC to match your actual trajectory..