Re: Actual B.C.
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Can you figure actual B.C. with just muzzle velocity and bullet drop at certain ranges?
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In short, yes. There is more to it than just that. You will need a very accurate or very close muzzle velocity as you have stated. Also you will need a VERY accurate zero. Preferably 200 or even better 300 yards to "iron" out the small things when dealing with a 100 yard zero. I will explain later. Next you will need precise atmosheric conditions. Temp, humidity, pressure. Then you fire your loads in 100 yard increments out to the maximum distance you will shoot tagets and/or game. Dont just go to your max range and call it good. I will also explain later. Then you can go to your ballistics program and input all the known variables. Next step is to adjust you drag model and BC untill the trajectory output is the same or as close as possible to your real drops.
Now the fun part. To figure out how many inches your bullets droped from zero, you can use the click adjustments or hold overs and do reverse math. For example, if it takes 100 clicks to hit dead on at 1000 yards from a 300 yard zero, and your using a true .25 MOA per click scope, your bullet dropped 261.75 inches from zero. You can convert holdovers as well.
Now on to explaining the longer zero. First there is nothing wrong with using a closer zero for general use. This is because you have spent time with the setup and know how it works and is of no consequense. When you are trying to find a true BC, you need more precision. The reason is that if your 100 yard zero is off 0.25" at 100 yards, this is typically an accecptable zero. But, and thats a heavy butt, that .25" makes for alot of error at 600 or 1K. A .25" error with a 300 yard zero is only a very slight issue at 6001K. So for finding a true BC, start at 300 yards and go from there. Then if you like, go back to 100 for general use.
Next topic to be explained. The reason you shouldnt go straight to your max range is because you can arrive at your max range with the same drop for several differant loads with vastly differant mid point trajectories. This is where using the correct drag model and BC come into play. There are many BC/drag combos that will give the same end result but differant mid point results. So in effect, you could miss a target at 750 yards because you didnt verify you mid point trajectory even though you would drill it at 1K.
As has been mentioned, you could just give the turret maker your drop info!
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Long range shooting is a process that ends with a result. Once you start to focus on the result (how bad your last shot was, how big the group is going to be, what your buck will score, what your match score is, what place you are in...) then you loose the capacity to focus on the process.
