Advanced Marksmanship How do I calculate a down range BC ?

[lobster]

Read an article about the need to recalculate your BC before the bullet goes transonic somewhere around 800 yards for a 168grFed match BTHP. It said to crono 20 shots then determine the difference btwn POA and POI. Then it said to " <span style="text-decoration: underline">take that info and determine your new BC</span>". HOW ??,The Author does not explain how to do that. How do you use that info to determine a new BC. Let's say I am 23 inches high and 18 inches left of POA. How does that info translate into a new BC. I will be using the Kestrel w/ Atrag. I can not see where this unit offers an input for a G7 BC. Let's just say I learn how to determine a new BC, Where do I input it too ? Into the G1 BC ? Would appreciate some help here.

 

[Chanonry]

Re: How do I calculate a down range BC ?

Pay the money and join the online training

 

[mouse07410]

Re: How do I calculate a down range BC ?

The advice to join the online training is good.

Theoretically computing a new BC is simple: you either measure velocity at the muzzle <span style="text-decoration: underline">and at the target</span> a few hundred yards down the range, or (less precise but easier to accomplish) measure muzzle velocity and the actual bullet drop at the target. Then you <span style="text-decoration: underline">plug that data into a ballistic calculator or program</span> such as Bullet Flight (or other programs, i.e. Quick Target Unlimited) - and <span style="text-decoration: underline">it will compute the new BC for you</span>. Your Atrag probably just doesn't have this capability, I don't know.

Unless you're already a pretty good shot (or your BC is G1 and comes from a manufacturer's brochure), I'd buy Bryan Litz book which lists banded G7 BC for many long range bullets and use those for the time being. <span style="font-style: italic">In fact I put my money where my mouth is, and bought that book myself. Eyeing the 2nd edition.</span>

 

[lobster]

Re: How do I calculate a down range BC ?

Thanks mouse07410 for the info provided. I am going to look further into the programs you mentioned and do plan on acquiring Bryan Litz's book as well. Frankly , I am not very comfortable setting up my crono down range, My luck, I would inenvertenly hit it !!! As far as on line training , I have yet to see any instruction along this line offered. Perhaps I have missed it. Thanks again though.

 

[blklabs]

Re: How do I calculate a down range BC ?

Lobster, the online training is a sub forum on this site that is a subscription service. It's well worth your money to join.

 

[lobster]

Re: How do I calculate a down range BC ?

Well blklabs, your the 3rd person now to make that suggestion to me. So I hear you guys loud and clear. I will look into it. Thanks for the suggestion.

 

[mouse07410]

Re: How do I calculate a down range BC ?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: lobster</div><div class="ubbcode-body">Thanks mouse07410 for the info provided. I am going to look further into the programs you mentioned and do plan on acquiring Bryan Litz's book as well.</div></div>
IMHO - money very well spent. Even though Bryan didn't provide enough of ballistic data for one to be able to write a complete - even simplified - calculator. The info he gives is very useful - and the actual BC for many bullets are priceless.

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">Frankly, I am not very comfortable setting up my crono down range, My luck, I would inenvertenly hit it!!!</div></div>
Don't feel bad! Many of us (me definitely included) feel (and are

) the same way.

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">As far as on line training , I have yet to see any instruction along this line offered. Perhaps I have missed it.</div></div>
Check this thread.

 

[blklabs]

Re: How do I calculate a down range BC ?

Lobster it sounded like you weren't familiar with the online training section. Just trying to help you out, not be repetitive. Good luck!