Does velocity affect ballistic coefficient?

waveslayer

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As mentioned above. Calculators are tools... sometimes you use different tools for different jobs. Yes I hardly ever dial because I prefer a H59 or Tremor 3 reticle. Makes follow up shots very easy, different when hunting because sometimes you only have one shot opportunity.

Calculators need to be trued, yes even the CDM or 4DOF. Why you use it as a tool is for weather conditions affecting the data. It will effect your ballistics, best is to shoot whatever bullet at 600 write down your dope and true the velocity to match your actual data.

Then go out to 1000 or so, 800 or 900 and change the BC to match your data, not velocity at this point. There's a good article on Snipers hide about trying your calculator and actual BC to each gun. BC's are gun specific hence why CDM sometimes is off. Because twist rates, velocity, etc all play a role in BC's.

Shoot and get real data then true your tool. Don't rely just on it.
 

muzzletalk

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As mentioned above. Calculators are tools... sometimes you use different tools for different jobs. Yes I hardly ever dial because I prefer a H59 or Tremor 3 reticle. Makes follow up shots very easy, different when hunting because sometimes you only have one shot opportunity.

Calculators need to be trued, yes even the CDM or 4DOF. Why you use it as a tool is for weather conditions affecting the data. It will effect your ballistics, best is to shoot whatever bullet at 600 write down your dope and true the velocity to match your actual data.

Then go out to 1000 or so, 800 or 900 and change the BC to match your data, not velocity at this point. There's a good article on Snipers hide about trying your calculator and actual BC to each gun. BC's are gun specific hence why CDM sometimes is off. Because twist rates, velocity, etc all play a role in BC's.

Shoot and get real data then true your tool. Don't rely just on it.
Waveslayer is right on the money. True up velocity at 600 and True BC 700+ yards.
 

david g ranes

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597
This is all great info fellas.....very valuable stuff for a guy like me who has hunted and shot rifles his entire life, but never tried long range shooting.
One other thing you might check is make sure you are dead on at your sight in range a half inch high isn’t that noticeable but multiplied down range pretty rapidly I was shooting a huskemaw scope adjustments aren’t that fine sighting in at 200 I was either hitting a little high or a little low so you have to figure that in. David
 

HVGBDT

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May 13, 2020
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Idaho
Thanks, Butter Bean. That makes me feel better. I thought that it might be too big of a difference and maybe had something else going on. I’m going to load more ammo and take it out to 800-1000 and see if my corrected BC holds.
That's what i had to do. I made adjustments out to 800 yds. When i corrected the bc to 800, it didn't change much moa at the closer distances. It finally makes sense to me about speed!
 

muzzletalk

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I only use the magneto for initial load development to true up QuickLoads. I get my 300 yd dope from the target and use weaponized math to get me out to 1k. I give my kestrel a general velocity, true my 600 yd MV and 1k BC. So the Magneto has its place, but true velocity will come from hits downrange.
 

ButterBean

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I only use the magneto for initial load development to true up QuickLoads. I get my 300 yd dope from the target and use weaponized math to get me out to 1k. I give my kestrel a general velocity, true my 600 yd MV and 1k BC. So the Magneto has its place, but true velocity will come from hits downrange.
We are way off topic Gentlemen
 

CONatureBoy

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Colorado
Nobody has commented yet about MagnetoSpeed chronograph accuracy:

1630445012386.png


So at velocities around 3,000 fps, your chronograph could be as much as 15 fps lower or higher than the reading. At 70 degrees F, sea level, 2" high scope, 200-yard zero, 0.284 bullet diameter, 145 grains, and a G7 BC of 0.230, the Berger calculator says the difference will be about a half-inch of vertical at 500 yards. That's not your three inches, but it's something. Depending on your ballistics calculator's features, a variety of other minor environmental factors (e.g. the Magnus effect, whereby a crosswind out beyond 200 yards could pull your shot upwards) might contribute another inch or two that your calculator doesn't account for. Litz's book (cited above) spells them out. You might want to figure out how much of the three inches that surprised you came from the environment, and how much from the gun and load. I would also be careful (1) not to hastily attribute all three inches to a single effect, and (2) to distinguish adjustments for muzzle velocity from adjustments to BC assumptions. In his Modern Advancements in Long Range Shooting, Vol. II, Litz says (p. 227), "A concept that many long-range shooters are familiar with is truing or calibrating the ballistic solver. . . . This process is necessary . . . where shooters may not have good information on their bullet's muzzle velocity or BC. . . . It is possible to determine MV with reasonable accuracy based on observed drop. However shooting to determine BC or drag is a very different thing which is much more difficult to do accurately." If you want precise (+/- 1%), empirically determined, velocity-dependent BCs for a given bullet, you'll usually find them in Litz's book, Ballistic Performance of Rifle Bullets, 3rd Ed.
 

ButterBean

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Lol. Off. I do bc all my load development and zeroing without it. I only put it on after all of that is done and shoot 10-15 rounds to get an average velocity.
Black just so you know all of the Hammers do this when you wick them up, I shot the 101 HBO's out of the RUM last week, I zeroed at 100 and dialed what was called [email protected] 400 and it shot .5Mil high, as I said I have seen this with all the Hammers I have shot, Speed drastically changes BC and I use the ballistic app's as a guideline and that's it, there's no app that I have seen yet that will accurately calculate for the Hammers , It's been conclusive with our test group
 

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