Ballistics question

[FeMan]

Jarhead,

Your method makes sense to do both. Is there a starting percentage you adjust the BC down once you've done the speed work at 6-700? Using the G7 of .354, adjust down 10% to .319 to start with? Or, is that to much at once? I've not tweak BC and don't know the reaction of lessening it 5-10%. I need to gain 6" at 1000 using the MV my LR throws.

I appreciate everyones input.

I think what Jarhead was suggesting is to shoot at 600 and change the velocity (and not the bc) in your software until the impacts line up with the prediction. Then, proceed to 1k (or farther is even better as long as you are not into transonic) and so the same thing but at that distance, leave the velocity alone and change the bc until things line up.

That is what I do and it gets me on the money out to 2k.

 

[JayHeater]

The shot is just west of true north.

 

[JayHeater]

Yes, I agree what Jarhead stated is my best path. Just a little time on a bc calculator and it makes the same sense as adjusting the speed. Looking forward to the results!

I shot this at 100 adjusting the zero from another rifle prior to testing at 800 and a 1000. I'm concerned it doesn't shoot high at distance... : )

 

[ebb]

What are you guys implying that bullet makers would give an overly optimistic BC of a bullet they are trying to sell you????? I just don't believe that could be true.

 

[Jarhead6870]

What are you guys implying that bullet makers would give an overly optimistic BC of a bullet they are trying to sell you????? I just don't believe that could be true.

I don’t know if you’re serious or not, but I don’t think anyone is implying or suggesting that BC numbers are being distorted for sales purposes by manufactures. BCs are dependent on bullet velocity; therefore they change. Manufacturers usually formulate their BC values at a given distance which translates to a given velocity for a particular bullet, barrel and load. Since barrel and load contribute to the velocity at a given distance, the BC calculated by manufacturers is not necessarily the BC that will work for your rifle/load and so, adjustments need to be made.

 

[ebb]

Many times data needs to be adjusted so that come ups are right, just as so many here including you and i have noticed. The problem i have with it is why do you never have to adjust the BC higher to make the come ups right?

 

[Jarhead6870]

If a BC is calculated at a distance closer than you are shooting, the BC will be higher because the velocity will be faster. The BC will need to be reduced as the velocity drops as the bullet travels farther. Sierra uses “stepped” BCs to compensate for velocity loss, Hornady has stepped information available on their site and Applied Ballistics offers users a custom drag curve to help match BCs to velocity.

It’s been my experience that using published BC information requires tweaking.