alternat method without a chrono--- ?

[Hugnot]

In the olden days, before electronic chronys that measured fleeting bullet shadows, radar imagery or changes in magnetic field, ballistic pendulums were used. Their use required some involved but simple math and exact measurements which all normal shooters except math geeks wanted to avoid. This resulted in comparisons of actual trajectories of same bullets at known ranges to estimate velocity.

 

[biednick]

Even if you chrono your rifle you need to use long range drops to true your result. Pretty much every ballistic calculator has a built in method for correcting muzzle velocity. You zero, enter your best guess for BC and velocity, shoot at a KD long range target, and enter the actual drop in the calculator. The calculator then changes MV to match the drop you entered.

Some people like to do it manually by changing the BC until their drops line up. It's a waste of time to do it that way. Whether you change BC manually or let the calculator correct MV automatically you'll get the same result.

 

[azarcher10x]

I know Geo Ballistics has a calculation for true muzzle velocity, doing

I dont currently have a chrono---- but I can estimate my velocity from the loading tables by interpolation. What if I just put a target out to say--- 500 yards---- shoot the target----- note the error in holdover and then go back to my drop-velocity- bullet weight tables and use the observed drop at 500 to see which curve I am matching. Then I can use that set of drops to make my range card. Would that get me in the ballpark ?
( I will get a chrono at some point)

I think I read where strelok was no longer available ?????
I thought I would buy a cheap used cell phone (not activated) as a dedicated platform for a ballistic program----- which one is a good basic one if strelok is not available any more ?

I know Geo Ballistics has a calculation for true muzzle velocity, doing just about what you're doing. I zero at 100, and then shoot 800. I give it the actual moa for 800, and it gives me the true muzzle velocity. Of course it's for that altitude, so make sure you have your pressure correct!

 

[Southern 62]

Good stuff to know!!! This forum has helped me many times.

 

[Catbrain]

this is all very good meat and potatos stuff----
I will probably get a chrono just to help in load development, but its nice to know it can be done old school too.

Thanks for all the info- I will watch the video later tonight.
I think the rifle and scope are capable--- so I just have to select some long places to place targets.

 

[skipglo]

I dont currently have a chrono---- but I can estimate my velocity from the loading tables by interpolation. What if I just put a target out to say--- 500 yards---- shoot the target----- note the error in holdover and then go back to my drop-velocity- bullet weight tables and use the observed drop at 500 to see which curve I am matching. Then I can use that set of drops to make my range card. Would that get me in the ballpark ?
( I will get a chrono at some point)

I think I read where strelok was no longer available ?????
I thought I would buy a cheap used cell phone (not activated) as a dedicated platform for a ballistic program----- which one is a good basic one if strelok is not available any more ?

Strelok is still available in non- North America sites...just downloaded to a new phone 3 weeks ago...

 

[Lenny Foffa]

Incredible thread and excellent responses. Apparently I have been looking at this in a far too simple manner. I "thought" the following; Ex; A 130 Grn Nosler Ballistic Tip with a G-1 BC of .433, fired from my 270 Win at a velocity of 3000 fps , at 800 ft in altitude at the rifle range, and at 50 degrees in air temp, that shooting a firm 100 yard Zero, results in a drop of 11 inches at 300 yards. ( JBM data ) So if I shoot a group at 300 yards , and the rifle prints 12 to 12.5 inches low ( instead of 11 inches low ) at 300 yards, then that is an indication that my Velocity would not really be 3000 fps, but more like 2875 to 2900 fps. "OR" the G 1 BC number is not correct.( unlikely) Although this simple math has been reliable for me up till now, I must learn these new concepts.

 

[Catbrain]

I have not dug into what all the different BC's mean--- but I heard the hornady guys saying that the BC is velocity dependent. That means its changing constantly as the bullet slows at distance. They also said that most of the BC
numbers are taken within the first few hundred yards or so.
Im going to have to study what the BC's are and how they work. Like everything else- gotta self educate

 

[Catbrain]

that was a great video on the G7 program !

 

[biednick]

Incredible thread and excellent responses. Apparently I have been looking at this in a far too simple manner. I "thought" the following; Ex; A 130 Grn Nosler Ballistic Tip with a G-1 BC of .433, fired from my 270 Win at a velocity of 3000 fps , at 800 ft in altitude at the rifle range, and at 50 degrees in air temp, that shooting a firm 100 yard Zero, results in a drop of 11 inches at 300 yards. ( JBM data ) So if I shoot a group at 300 yards , and the rifle prints 12 to 12.5 inches low ( instead of 11 inches low ) at 300 yards, then that is an indication that my Velocity would not really be 3000 fps, but more like 2875 to 2900 fps. "OR" the G 1 BC number is not correct.( unlikely) Although this simple math has been reliable for me up till now, I must learn these new concepts.

There's a very good chance your BC is wrong. BC is dependant on velocity, and if you're not running your bullets at the same velocity as the manufacturer you'll see a different BC. On long shots it may change by a meaningful amount down range as velocity drops. Applied Ballistics' PDMs and CDMs account for this. It doesn't matter though, true your MV at the longest range you plan to shoot and you'll be fine.

 

[LongBomber]

Take one tall target - like 50" tall. Dot at the top and shoot a group at 100-150-200-350-300 etc. till you get out to 500y. Easy to directly measure the drop on one target without your rifles zero coming into play.
You can build a drop card off that dats or
if you are running a bullet AB has a listed g7 bc for put that in the system along with your rifles details and measured enviro's and you will get very close when building a profile in any of the ballistic programs.

 

[Catbrain]

i do have a monster big piece of cardboard I have been saving

 

[Bravo 4]

Even with a chrono'ed load you may need to tweak things. Your BC may differ from manufacturer's advertised and your scope's turrets may not yield 100% correct adjustments. A quick method I and many others use is to ensure a good zero (I do 100 yards), shoot to 400 or 500 depending on cartridge/load and adjust muzzle velocity to match drops (velocity is king to this point), then shoot 800 or 1000 and adjust BC to match. Or I can spend a large amount of time and do it "right".