How to true the BC

[7.62 Gunner]

That's good stuff! If I'm starting at 2770 it isn't long before my bc is down closer to .700…or do I work off G7? Back to my original question, how do I true up my bc to match my actual rifle.

I use the Hornady ballistics app, the other week when I tested the 180 eldms at 1340 I'd chronoed the velocity at 2820.
I impacted approx 1 moa low, and after reducing the velocity by 20 fps everything jived. I was having the same issue with low impacts from Bergers as well which also were due to inflated velocity.

I did a tracking test on my scope to verify it was calibrated, definitely do a tall target test if you haven't already.
I believe hornady uses an average BC that's lower than .796 in their calculator, I'd be curious how the Hornady app compared to what your calculator is saying.

 

[AggieHunter]

It doesn't matter what your binos say. Step 1 -Go to 100 yards and shoot a group that hits perfectly at the zero - no high or low shots. Know your velocity. Step 2 - Without touching your zero, go to 500 yards, aim at a target, shoot 3 shots (do not measure velocity), Very important - measure the average drop in inches from your aim point. Step 3 - Darrell Hollands "https://www.hollandguns.com/HollandsUltimateDataCardGenerator.html" to adjust your BC and develop a new data card. It is easy, simple and works every time for every kind of bullet.

 

[skipglo]

I run my own custom curve from stepped velocities exactly as printed in this book simply adjust your velocity and everything should match up. The ballistics app Shooter allows you to set up and run multiple Bc's others will not.

X2......easier for me and I find more accurate at distance. Chronographs tell you what's happening within 20 ft ( or 10" depending on which one you use) so I, like The Dude , adjust speed to the distance witnessed.

 

[338 dude]

Adjust velocity to 600 adjust BC beyond that

 

[Taylorbok]

That's good stuff! If I'm starting at 2770 it isn't long before my bc is down closer to .700…or do I work off G7? Back to my original question, how do I true up my bc to match my actual rifle.

Use G7.
To true your BC here is what I would do, shoot through your Chrono put that into your calculator with what ever BC is on the box, go to 600 yards and see what your actual DOPE is vs what the calculator spit out, adjust the muzzle velocity in your calculator until the numbers match. Now you need figure out at what distance your bullet goes transonic, your calculator should be able to show you this number. Find a target 80% that distance and shoot it, and compare actual dope to calculator, adjust BC in calculator until they match. now go back to 600 and make sure everything still lines up.

 

[Eric_F]

Adjust velocity to 600 adjust BC beyond that

This will be counter-productive if you have chrono-measured speeds. If you're going off factory ammo box velocity, sure. G7, ideally at a few different velocity bands, or a full custom drag profile is the best way.

 

[Ucsdryder]

It doesn't matter what your binos say. Step 1 -Go to 100 yards and shoot a group that hits perfectly at the zero - no high or low shots. Know your velocity. Step 2 - Without touching your zero, go to 500 yards, aim at a target, shoot 3 shots (do not measure velocity), Very important - measure the average drop in inches from your aim point. Step 3 - Darrell Hollands "https://www.hollandguns.com/HollandsUltimateDataCardGenerator.html" to adjust your BC and develop a new data card. It is easy, simple and works every time for every kind of bullet.

This method seems the easiest… I'm curious why you chose 500? Are you choosing the longest distance that you can reliably shoot a solid group?

 

[338 dude]

This will be counter-productive if you have chrono-meadured speeds. If you're going off factory ammo box velocity, sure. G7, ideally at a few different velocity bands, or a full custom drag profile is the best way.

This will be counter-productive if you have chrono-meadured speeds. If you're going off factory ammo box velocity, sure. G7, ideally at a few different velocity bands, or a full custom drag profile is the best way.

 

[kgunz11]

If you have a good chrono, there's no need to ever adjust your MV.
Adjust the BC until impacts on target match. It's usually good to do that from 800-1000 yards.

Remember, the published BC is an average collected during testing. Several factors can affect the BC like twist, numbers of lands/grooves, condition of the bore, etc..

Your rifle barrel is unique so adjusting the BC in your ballistics solver to match your impacts is the most accurate method.

 

[pony doctor]

I imagine this has been discussed before but a quick search didn't come up with anything recent!

I am using a ZEISS rf10x42 that calculates elevation and atmospheric conditions, into the ballistic calculator. I am always low on my shots past about 600 yards, give or take. A couple weeks back I was shooting at 1250 and was hitting a good 16" low. My muzzle velocity is on per my magneto v3 so I'm thinking the 180 eldm doesn't have quite the BC advertised. I guess the easy way would be to shoot at 900 yards and fidget with the bc calculator until it gives me the same mil correction. Is there a better way? I don't have access to another chrono and the magneto doesn't work downrange.

Am I missing something here in this great discussion? Truing the velocity based on drop at say 1000 yards seems logical but just FWIW, let's assume you have a 1/2 Moa rifle ( either best the rifle can do or best shooter skill set). That bullet should land somewhere in a 10 inch circle if you perfectly account for the wind! So long as the target has kill zone of this size, all is good provided you have the velocity required for the bullet to perform as intended. Shooting paper is great practice and challenges one's skills but….. ethical hunting has it's limits in my opinion. Bottom line, in my opinion; threads like this one have great " food for thought" applicable to most all purposes when deciding to pull that trigger.

 

[Ucsdryder]

Am I missing something here in this great discussion? Truing the velocity based on drop at say 1000 yards seems logical but just FWIW, let's assume you have a 1/2 Moa rifle ( either best the rifle can do or best shooter skill set). That bullet should land somewhere in a 10 inch circle if you perfectly account for the wind! So long as the target has kill zone of this size, all is good provided you have the velocity required for the bullet to perform as intended. Shooting paper is great practice and challenges one's skills but….. ethical hunting has it's limits in my opinion. Bottom line, in my opinion; threads like this one have great " food for thought" applicable to most all purposes when deciding to pull that trigger.

I'm confused by your post. It sounds like you are trying to turn this into a hunting distance ethics argument? This has nothing to do with hunting. It's a topic on getting a rifle dope to match the ballistics that the manufacturer provides.

 

[Ckleeves]

It doesn't matter what your binos say. Step 1 -Go to 100 yards and shoot a group that hits perfectly at the zero - no high or low shots. Know your velocity. Step 2 - Without touching your zero, go to 500 yards, aim at a target, shoot 3 shots (do not measure velocity), Very important - measure the average drop in inches from your aim point. Step 3 - Darrell Hollands "https://www.hollandguns.com/HollandsUltimateDataCardGenerator.html" to adjust your BC and develop a new data card. It is easy, simple and works every time for every kind of bullet.

Just my .02 but i have never had luck with trueing BC at 500 yards. Run it though a calculator and you will see what I mean. A .010 change in G7 BC at 500 yards results in only a little bit over 1/4" change in impact. Whereas at 1000 yards It's 4" so you start to get into something measurable.

This is with a bullet I already had loaded in my kestrel just fyi not the OP's. That same 1/4" on the target from adjusting the BC by .010 can also be manipulated by 7fps of velocity so a guy would have to have fantastic SD's and be a great shot to really get anything meaningful out of it.

It's already been said but velocity to 500-600 and bc beyond that.

 

[XLR Industries]

That's good stuff! If I'm starting at 2770 it isn't long before my bc is down closer to .700…or do I work off G7? Back to my original question, how do I true up my bc to match my actual rifle.

Use your G7 and then adjust the BC. The magnetospeed is giving u a fixed measurement so you know that is correct (as long as it is doing its job). The BC is going to change depending on your barrel. A barrel could have a tighter bore, different twist, different numbers of lands, or different shaped lands. Every one of those is going to change your BC in one way, shape, or form. There isn't really a great way to change BC without just guessing and checking. Typically what I do is shoot at 1200 to get my initial BC. Then I will confirm it at 500, and 800 to make sure that elevation is good at those distances. We have an article explaining the different ways we have found that work so I will put a link below!

Truing Rifle Data

This is the time of the year when shooters start getting the itch. It is the best time to start brushing up on your wind calls and making sure that your rifle is shooting well! One common question that we get asked is how we true our data when we gather dope. This is a great question because...

xlrindustries.com

 

[Ucsdryder]

Thanks guys! Has anybody ever mentioned how great this place is?