Trueing muzzle velocity vs BC

[Bravo 4]

There is definitely a lot going against the shooter. From inaccurate/inconsistencies in turret adjustment, scope and/or rifle cant, azimuth to target- latitude- Coriolis/Eotvos, AJ, SD in velocity and/or BC, wind speed and velocity, angle to target, changes in altitude/temp/BP/humidity, blah-blah-blah (not to mention anything shooter related!). It's amazing we can hit anything of relatively small size at anything other than moderate distances, yet here we are. We can tweak and tune and obsess over all the minutiae and still miss. Or things can just come together and amaze even a seasoned shooter. Last time I helped my buddy with a rifle he handed me a new factory Tikka and a box of factory Hornady ammo. I mounted a Vortex scope, did a quick bore sight through the barrel at a 100 yard target, shot 3 into a really small group, made a quick adjustment to center, shot another really small group, input the manufacturer's velocity into my phone app and proceeded to shoot a really small group at 500 exactly where I was aiming and then did the same at 800, handed him the rifle and said don't touch anything! 12 rounds and all was done for as far as I think that rifle needs to be shot at deer, his intended target.

 

[skipglo]

This seems like the time of the year when guys start getting the long-range shooting urge. It is the best time to start practicing and brushing up on your wind calling skills! One common thing that I get asked a lot is whether to true the BC or Velocity? What is your preffered method for dialing in your long range rifle? Do you trust what the chronograph says and true BC from there? Do you true velocity to 600 and then BC after that? Or do you strictly true velocity because BC is a measurement that has been taken by a multiple $1000 tool by the big bullet companies?

I true velocity....BC should be CLOSE to what the manufacturer states, but without a Chrony...velocity is the unknown number so I true it to what the target is telling me.

 

[gohring3006]

I map the scope tracking first, then true velocity to 800 then true BC. Gotta have the scope true or you'll chase your tail for a minute and waste ammo.

 

[XLR Industries]

I true velocity....BC should be CLOSE to what the manufacturer states, but without a Chrony...velocity is the unknown number so I true it to what the target is telling me.

That is a great point to bring up! If you do not have a chrono, I feel like you have to true velocity to most distances! You will chase your tail a little bit but can definitely get accurate results still!

 

[waveslayer]

I think you meant true velocity at 600 correct?

Yes sorry, my fat donut greased fingers weren't keeping up with my mind.

True velocity first for the first 600 and then BC past 800 to 1000 or so.

I have a profile set up past 1,000 where I trued velocity at 800 and BC past 1200 to get the stars to line up

 

[Greyfox]

Given my scope has been tested for tracking, and my load thoroughly developed, I will starts with my recorded velocities and the bullet manufacturers BC. I will then true velocity with my ballistic calculator at 500 or 600 yards IF necessary. I will then do the same with BC at 800-1000 yards. I have high confidence in the BR2/BR4 and Sig2400 ballistic rangefinders, finding them very effective for my +1000 yard hunting/shooting which ranges in elevation from 300ft-5000ft, and temperatures from 0-80F.

 

[kgunz11]

I trust my chronograph. I have several and have compared them against each other. I use the speed given from the chrono and true the BC and it works out to 1760 yards.

The BC published by the bullet manufacturer is an average. Several things can effect the BC of the bullet to include the condition of the bore of the barrel which changes over time.

I'm not one to argue with a measuring tape. If I tell you to cut a 6" piece of board, are you going to cut it at what looks like 6" or are you going to cut where the measuring tape says? The chrono is the measuring tape, and I don't argue with the tape.

 

[coop2564]

I get my chrono's velocity and the bullet BC then verify @500 since that's my ranges longest distance. Then I use the trued velocity from that in App.

 

[Starlite]

This seems like the time of the year when guys start getting the long-range shooting urge. It is the best time to start practicing and brushing up on your wind calling skills! One common thing that I get asked a lot is whether to true the BC or Velocity? What is your preffered method for dialing in your long range rifle? Do you trust what the chronograph says and true BC from there? Do you true velocity to 600 and then BC after that? Or do you strictly true velocity because BC is a measurement that has been taken by a multiple $1000 tool by the big bullet companies?

I use this meathod.

 

[Starlite]

I use this meathod.

Should also state that truing at 600M is what I used to do. FWIW I don't see any difference which is likely due to me. Still kills critters though.

 

[tony d willIiams]

I start with the numbers provided by bullet and powder manufacturers.

They do not use the brass I use, the barrel, action, or scope I use. Neither do they get their data from the altitudes, temperatures, GPS locations, or directions and angles I shoot. And I keep my "rounds" against" my body so the temperature is fairly stable and reproducible in the field.

Then I adjust for my equipment. I take my own readings and data. I run the numbers, and check that the target tells the same story as my collected information states.

Yes, I am anal. Used to bother my wife, but after I made a bunch of handicap equipment for our special needs adult child, she is happy about it.
I am also stupidly optimistic, her words, said with a grin.

Edit: Tomorrow I am heading out to the Yuma Proving Grounds. I will bring carnitas with me for Cinco de Mayo, and leave enough at home. I will be starting my practicing with long guns. After a few days, shooting and tracking, back to home. It is good to be retired.

 

[dfanonymous]

That is a great point to bring up! If you do not have a chrono, I feel like you have to true velocity to most distances! You will chase your tail a little bit but can definitely get accurate results still!

Only if you don't know what you are doing. Using centerfire cartridges, you will always be super sonic around 600y. Between 600-900y you can true velocity data in mils or moa using most software. Using published BCs usually.

That pretty much eliminates 90% of this forums members problems.

For everyone else it becomes a matter of poors vs non poors. Stubborn vs progressive shooters. Whatever you wish to call it. You can use a series of different BCs to establish dopes in the g1-g7 range as trued data, or alternatively like me, one can use a AB custom curve, and tweak DSF to be good out to the bullets complete usable flight, regardless of distances. Hence where the kestrel comes to play.

Now a days, you don't even really need a chronograph to get dope. Just a starting point.

 

[BrentM]

Now a days, you don't even really need a chronograph to get dope. Just a starting point.

Def some truth there. Back in the old days chrono's weren't really a thing since few us had them and they weren't very good anyway. Load ladder or ocw, confirm zero, shoot for drop data, confirm, done.

Today you can use a good chrono like lab or mag and determine velocity node and sd in less than 30 rounds that prints repeatable highly accurate groups to 1000 without much issue. After that the best thing is just shooting in a wide range of conditions to ensure you stay salty and yet humble. Ha ha. I get a lot of humble pie in winter mountain shooting. Ugh

 

[DocB]

This seems like the time of the year when guys start getting the long-range shooting urge. It is the best time to start practicing and brushing up on your wind calling skills! One common thing that I get asked a lot is whether to true the BC or Velocity? What is your preffered method for dialing in your long range rifle? Do you trust what the chronograph says and true BC from there? Do you true velocity to 600 and then BC after that? Or do you strictly true velocity because BC is a measurement that has been taken by a multiple $1000 tool by the big bullet companies?

Tagging in!