BDC retical calibration??

[KootenayNewb]

So this may be a stupid question, and/or I may be over thinking it again but I'm a newb so whatever.

How are the hashmarks on BDC reticals calculated when different calibers, and even different ammo of the same caliber, have different ballistic trajectories? Is it mostly an estimated average for holdover and each shooter gets to know how the scope fits their particular rifle?

Speaking in terms of hunting situations with larger than rimfire calibers.

 

[Suther]

Yup. An average. Usually the manual will give more info. For example, my vortex lists two different velocity ranges, and you're expected to zero @100 for the slower stuff and @200 for the faster stuff.

Obviously this won't be spot-on at longer ranges though. You'll have to actually shoot at those ranges to figure out how close it is. You can also use the information gained from that to calculate the specific range for your given load - eg the 400yd hash might be 380yds for your specific load.

 

[PGW Steve]

At a known distance, say exactly 100 yards or meters, place a graduated target. With the rifle well supported, take note of the actual position of each sub-reticle. You now have a map of the reticle in terms of 'MOA' or MILs. Run whatever calibre you want to know about through your favorite ballistic app, and set the distance increments small enough to give the desired resolution. You can now pick the distance that corresponds with each sub-reticles drop, and make your own custom chart.

 

[snooker]

In the vast majority of cases, Bullet Drop Compensator (BDC) reticles
must be set to maximum magnification for the holdover points to be somewhat accurate as well.

 

[Pointdexter]

Ignore the distances that are given in the scopes manual. The BDC measurement is in minutes of angle (MOA). When the user takes the bullet data (BC, velocity, weight, etc) and runs it through a ballistic calculator one of the columns that gets filled out is the minutes of angle (MOA), and on that row is the actual distance your bullet will travel to at that particular point.

Shooterscalculator.com is a good one to try out

 

[KootenayNewb]

At a known distance, say exactly 100 yards or meters, place a graduated target. With the rifle well supported, take note of the actual position of each sub-reticle. You now have a map of the reticle in terms of 'MOA' or MILs. Run whatever calibre you want to know about through your favorite ballistic app, and set the distance increments small enough to give the desired resolution. You can now pick the distance that corresponds with each sub-reticles drop, and make your own custom chart.

Just to say it back so I understand. On one of these type targets, I could 100y zero on one of them, then on another take a shot or a group while holding at the next sub-reticle (200y). In theory and with a perfect fit that shot or group should hit 3.9 inches high on the target, and the 300y group should hit 14.6" high.

My initial thought is that at 100y the bullet flight is still too flat to accurately represent the drop the bullet will take over the longer yardage shots.

 

[PGW Steve]

Just to say it back so I understand. On one of these type targets, I could 100y zero on one of them, then on another take a shot or a group while holding at the next sub-reticle (200y). In theory and with a perfect fit that shot or group should hit 3.9 inches high on the target, and the 300y group should hit 14.6" high.

My initial thought is that at 100y the bullet flight is still too flat to accurately represent the drop the bullet will take over the longer yardage shots.

You need to use MOA of drop, not inches. If you use inches, you need to convert it to MOA. If you're using inches to calibrate your reticle as I described earlier, divide the 3.9 by 2 and the 14.6 by 3. This will give you 1.95" and 4.86" of height. So that is correct, but only if your sub-reticles are 1.95 and 4.86" below the main stadia. You need your reticle dimensions and work from there, the distances most likely won't be a round number for each hash mark.

 

[Suther]

In the vast majority of cases, Bullet Drop Compensator (BDC) reticles
must be set to maximum magnification for the holdover points to be somewhat accurate as well.

To be specific, if it's a Second Focal Plane scope (SFP) then there will be a specific magnification where the reticle is calibrated. This is USUALLY the max magnification, but isn't always - I've seen a 6-24x that was "correct" at 18x for example.

 

[KootenayNewb]

Ignore the distances that are given in the scopes manual. The BDC measurement is in minutes of angle (MOA). When the user takes the bullet data (BC, velocity, weight, etc) and runs it through a ballistic calculator one of the columns that gets filled out is the minutes of angle (MOA), and on that row is the actual distance your bullet will travel to at that particular point.

Shooterscalculator.com is a good one to try out

So with this data my "200y" hashmark should hit 1.88 moa high when shot at the center of a 100y zeroed target?

 

[Camoman1]

To be specific, if it's a Second Focal Plane scope (SFP) then there will be a specific magnification where the reticle is calibrated. This is USUALLY the max magnification, but isn't always - I've seen a 6-24x that was "correct" at 18x for example.

This

You’ll have to test to see what magnification works with each load, depending on the load it was designed for it may not be very accurate at every distance.

 

[KootenayNewb]

You need to use MOA of drop, not inches. If you use inches, you need to convert it to MOA. If you're using inches to calibrate your reticle as I described earlier, divide the 3.9 by 2 and the 14.6 by 3. This will give you 1.95" and 4.86" of height. So that is correct, but only if your sub-reticles are 1.95 and 4.86" below the main stadia. You need your reticle dimensions and work from there, the distances most likely won't be a round number for each hash mark.

Right, gotta think in terms of moa not inches. Are the distance between the hashmarks generally stated in moa in the manuals? If so, I then convert the scopes moa setup to my rifle/ammo characteristics and get an idea of the inches each hashmark progression represents.

 

[Beeron]

I have gotten rid of all the scopes I used to have with BDC reticles in favor of standard hashed stadia.
All my stadia now have hash marks for 2-4-6-8-etc MOA.
I develop a load, shoot 5 rounds past my Garmin, plug that data into my BC and it spits out MOA drop to as far as I want to shoot.
I dial it and whammo.
So far so good.

 

[Pointdexter]

View attachment 1097325
So with this data my "200y" hashmark should hit 1.88 moa high when shot at the center of a 100y zeroed target?

You're almost there. Your reticle should have a manual that shows what MOA value each hash mark is from the center crossbar. If it's a vortex scope, I'm going to guess that the values are as follows:

Crosshair: 0moa (100 yards)
First line: 1.5moa (186ish yards)
Second line :4.5moa (304ish yards)
Third line: 7.5moa (403ish yards)
Top of bottom post: 11moa (506ish yards)

If you replug in your 165gr corelokt data to the calculator, and then select your chart step size as "1" you'll find your distances at those MOA values.

Edit: I did it for you.

 

[blackburbot]

The calibers and bullet combinations that are listed in the instruction manuals pretty much have the same drops. If you are trusting the BDC reticle to line up to actual impacts, you are just hoping for the best to start with.

Almost safer and easier to go with a further zero, like 200-250 yards so you have less guessing out to 300-350 yards because the bullet is only +/- 4"

Then once past that distance actually use proper drops

 

[KootenayNewb]

I think

You're almost there. Your reticle should have a manual that shows what MOA value each hash mark is from the center crossbar. If it's a vortex scope, I'm going to guess that the values are as follows:

Crosshair: 0moa (100 yards)
First line: 1.5moa (186ish yards)
Second line :4.5moa (304ish yards)
Third line: 7.5moa (403ish yards)
Top of bottom post: 11moa (506ish yards)

If you replug in your 165gr corelokt data to the calculator, and then select your chart step size as "1" you'll find your distances at those MOA values.

Edit: I did it for you.

I think I'm getting it. Using a ballistics calculator I enter my ammo data then cross reference the ranges it states that the bullet will travel at a specific moa to the specs of my scope.

Quick and dirty example:
My calculator tells me that cartridge blahblahblah will fly 280ish yards which will be equivalent to 4moa above my 100y zero. It also tells me that aiming at my target with the center of the crosshairs my shot will fall about 11.5" low. My scope manual tells me that when zeroed at 100y the 3rd line below center equals 4moa.

In the hunting field I could expect to hold that 3rd line center of my target and hit in the kill zone of a deer and larger game that is between 250-300 yards, (+/- 4" of the stated 11.5" low). With zero wind and a perfect shot.

Or I could dial my 1/4moa scope up 16 clicks and aim with the center of the crosshair.

 

[KootenayNewb]

The calibers and bullet combinations that are listed in the instruction manuals pretty much have the same drops. If you are trusting the BDC reticle to line up to actual impacts, you are just hoping for the best to start with.

Almost safer and easier to go with a further zero, like 200-250 yards so you have less guessing out to 300-350 yards because the bullet is only +/- 4"

Then once past that distance actually use proper drops

At this point, and with the rifle I have 300 will be my absolute max! Have yet to pull the trigger on any game and my local range only goes out to 200. I'm hoping that I'll be able to hunt in the 50-200 range.

 

[todbartell]

JBM ballistics is a really good site for making reality jive with your BDC

Hopefully this makes sense, I highlighted what you need to do to make sure your 2nd line down bang on at 400 yards (4.5moa below center intersection of reticle) when the optic is on highest magnification (SFP) ~ 6.5 Creedmoor 143gr ELDx 2700 fps MV

Yellow highlights are what you generally want to input, pink is to put your zero for the desired MOA below main crosshair

Pink highlights ^ are where your first line will be (290Y), second line bang on 400y, third line 500y, tip of post 600Y

It's almost like Vortex designed their BDC around the 6.5cm flash in a pan LOL

I'll post up another cartridge that won't jive as well, just to show the BDC will work with anything

 

[KootenayNewb]

JBM ballistics is a really good site for making reality jive with your BDC

Hopefully this makes sense, I highlighted what you need to do to make sure your 2nd line down bang on at 400 yards (4.5moa below center intersection of reticle) when the optic is on highest magnification (SFP) ~ 6.5 Creedmoor 143gr ELDx 2700 fps MV

Yellow highlights are what you generally want to input, pink is to put your zero for the desired MOA below main crosshair

Pink highlights ^ are where your first line will be (290Y), second line bang on 400y, third line 500y, tip of post 600Y

It's almost like Vortex designed their BDC around the 6.5cm flash in a pan LOL

I'll post up another cartridge that won't jive as well, just to show the BDC will work with anything

At this point I'm still scope shopping, most likely get something basic. When I get something I'll revisit this thread and get my gear dialed for the hunting I plan on doing. Thanks for the input!

 

[savagelh]

Strelok is another app that works great for finding what distance your hash marks are good for. Just make sure you have good data to input.

 

[todbartell]

JBM ballistics is a really good site for making reality jive with your BDC

Hopefully this makes sense, I highlighted what you need to do to make sure your 2nd line down bang on at 400 yards (4.5moa below center intersection of reticle) when the optic is on highest magnification (SFP) ~ 6.5 Creedmoor 143gr ELDx 2700 fps MV

Yellow highlights are what you generally want to input, pink is to put your zero for the desired MOA below main crosshair

I'll post up another cartridge that won't jive as well, just to show the BDC will work with anything

info for same reticle, but 30-06 200gr Nosler Partition @ 2550 fps MV

Adjusting impact so the first line down will be bang on at 300 yards when scope is on highest magnification

:

This takes a 250 yard zero, first line on at 300y, second line would be 390Y, third line 470Y, and tip of post = 550Y