G7 BCs on 20cal Vmax

[ab_bentley]

Anyone have the G7 on the 40gr Vmax. Past 500yds the G1 doesn't hold true, by my calculations it's about .050 less on the G1 BC, which leads me to using the G7.

Adam

 

[Phil]

Shoot Brian a PM and see.......

I can`t seem to come up with anything on my company restricted computer......


Phil.

 

[ratbuster]

Anyone have the G7 on the 40gr Vmax. Past 500yds the G1 doesn't hold true, by my calculations it's about .050 less on the G1 BC, which leads me to using the G7.

Adam

I spoke to a tech at hornady about this. He said the G1 is more appropriate than G7 for the 20cal 40gn Vmax

 

[ab_bentley]

I spoke to a tech at hornady about this. He said the G1 is more appropriate than G7 for the 20cal 40gn Vmax

Gracias, I guess I'll just keep using the .215 bc.

 

[XBBR Shooter]

Anyone have the G7 on the 40gr Vmax. Past 500yds the G1 doesn't hold true, by my calculations it's about .050 less on the G1 BC, which leads me to using the G7.

Adam

Try G7 = 0.118 as a starting place, but I shoot the 40 V-Max and I agree that it is not a G7.

If the G7 of 0.118 doesn't get you in a better tracking profile, go back to the G1 of 0.275, and tweak the BC until the predictions are tracking the bullet's actual drop.

 

[Auto-X Fil]

Anyone have the G7 on the 40gr Vmax. Past 500yds the G1 doesn't hold true, by my calculations it's about .050 less on the G1 BC, which leads me to using the G7.

Adam

Yup, G1 is probably a better fit with that tiny BT, but won't jive with the steep spire nose. I would suggest using a stepped BC based on velocity to get your calulations to work out.

How sure are you that your scope tracks and that your velocity numbers are correct? Scope tracking errors are the #1 reason I see "BC errors" in calculations. Although, in this case the bullet is an odd-ball shape.

 

[ab_bentley]

Yup, G1 is probably a better fit with that tiny BT, but won't jive with the steep spire nose. I would suggest using a stepped BC based on velocity to get your calulations to work out.

How sure are you that your scope tracks and that your velocity numbers are correct? Scope tracking errors are the #1 reason I see "BC errors" in calculations. Although, in this case the bullet is an odd-ball shape.

99% sure the scope is solid. I thought the same, the scope was inducing error. Ran the plumb bob test and tracked on the nose. I know my speed is 3855 on the nose with single digit ES/SD readings. Started messing with the bc in the calculator and presto, 600yd hits were happening on the first shot. The kicker though is at 100yds that 500yd+ BC doesn't hold true. Typically it results in a much higher shot, 1 moa too high in most cases. I'm basically having to run two BCs for the same gun at different distances.

Adam

 

[XBBR Shooter]

99% sure the scope is solid. I thought the same, the scope was inducing error. Ran the plumb bob test and tracked on the nose. I know my speed is 3855 on the nose with single digit ES/SD readings. Started messing with the bc in the calculator and presto, 600yd hits were happening on the first shot. The kicker though is at 100yds that 500yd+ BC doesn't hold true. Typically it results in a much higher shot, 1 moa too high in most cases. I'm basically having to run two BCs for the same gun at different distances.

Adam

Is it shooting flatter past 500 than the G1 predicts?

 

[ab_bentley]

Is it shooting flatter past 500 than the G1 predicts?

At least .75 MOA. That was with the .275 advertised BC. I went to the .215 bc (concluded via group height/speed vs used moa) and it started making sense. Prior to that I had slowed the speed from 3855 to 35xx and that did the trick most of the time, but i knew my speed was accurate, so the bc had to be incorrect.

 

[ab_bentley]

At least .75 MOA. That was with the .275 advertised BC. I went to the .215 bc (concluded via group height/speed vs used moa) and it started making sense. Prior to that I had slowed the speed from 3855 to 35xx and that did the trick most of the time, but i knew my speed was accurate, so the bc had to be incorrect.

Basically the other option is this is brought on by reduction of speed not calculated for. Maybe my program can't understand that i want a 40gr bullet to impact a target 600yds away using the set parameters.
I'm using Strelok pro.

Adam

 

[fredo]

I'd just map out your real world dope & use that.

Your situation brings to light that, sometimes, there is a limitation to how a generic B.C. profile doesn't always jive with a particular bullet design/shape. Trying to 'tweak' the B.C. might get ya close, but it'd be like catching your tail after chasing for a while...

Beyond that, the big brain dudes who are using Doppler to map B.C. curves don't really mess with testing/proving .20 cal bullets. So, there goes any hope of enjoying a 'custom curve' data point to reference with an AB based app...

Course, you could try data input into some different ballistic apps, and see if they'll generate a dope that's closer to your real world? Seeing as how many apps use the JBM engine, that avenue is a crapshoot. An app like Trasol uses a different engine, maybe that would work?

But pretty much, the easiest end around is to make a hard copy of your actual field proven dope, and run with it.

To add:
That little bullet doesn't take much in the way of environments to affect trajectory. Shooting across hot ground, over a low spot, in a headwind/tailwind, etc. could skew your drops enough to matter in the 5-600yd range. No ballistic calculator can account for those potential factors. Something else to keep in mind when launching a tiny bullet...

 

[ab_bentley]

I'd just map out your real world dope & use that.

Your situation brings to light that, sometimes, there is a limitation to how a generic B.C. profile doesn't always jive with a particular bullet design/shape. Trying to 'tweak' the B.C. might get ya close, but it'd be like catching your tail after chasing for a while...

Beyond that, the big brain dudes who are using Doppler to map B.C. curves don't really mess with testing/proving .20 cal bullets. So, there goes any hope of enjoying a 'custom curve' data point to reference with an AB based app...

Course, you could try data input into some different ballistic apps, and see if they'll generate a dope that's closer to your real world? Seeing as how many apps use the JBM engine, that avenue is a crapshoot. An app like Trasol uses a different engine, maybe that would work?

But pretty much, the easiest end around is to make a hard copy of your actual field proven dope, and run with it.

To add:
That little bullet doesn't take much in the way of environments to affect trajectory. Shooting across hot ground, over a low spot, in a headwind/tailwind, etc. could skew your drops enough to matter in the 5-600yd range. No ballistic calculator can account for those potential factors. Something else to keep in mind when launching a tiny bullet...

That's pretty much the conclusion I've come to. Adam

 

[vmaxpro]

That's pretty much the conclusion I've come to. Adam

Adam do you happen to know the g7 of the 30gr kindler golds? G1 doesnt add up with them at all

 

[ab_bentley]

Adam do you happen to know the g7 of the 30gr kindler golds? G1 doesnt add up with them at all

I don't, i bet Todd would know. It would actually surprise me if he didn't.