As I said in my first post, we enter all the data, if we have it right, the only thing it can be is our actual BC. Is this correct?
RR
To be technical, NO. For practical applications, yes. This practical application is why I answered yes originally and I stand by this.
As a side note, I believe Bryan and RR are both correct.
Also as a side note, to back up Bryan on this point, scope imperfections can and will give you a percieved BC that is more or less than reality. This really is of little to no consequence (at least out to 1K AND minus accurate impact velocities. More on that later). As long as you are doing things consistently and taking into account the actual air density.
Before everybody lights the flame thrower, let me elaborate.
Lets say you go to the range and develop your load, get your average velocity, set your zero and then go to "find" your BC at long range. You set up at your zero for quick confirmation. Then your program tells you based on the published BC (.507) that your 1000 yard drop is 211" low. Knowing your scope is calibrated in .25 MOA values, you click it 81 times. But because there is an imperfection in your scope and the value is really .260 MOA you only needed 78 clicks. This will cause an impact of about 7.5" High so your "percieved" BC works out to about .535. As long as you use .535 AND adjust in the field in the same manner you did during the tests, you will be scarry close. Technically, it is wrong but for ALL practical use, it works. This is the method I prefer over ALL other methods. I have used the double chrony to verify the actual BC of a bullet but when it comes to setting up on a real world long range shot, I always use the numbers found in the drop tests. If there are imperfections in my scope, they get absorbed into my BC or better yet, my "percieved" BC.
As another side note. I have used double chronies to come up with actual BC's and are usually close to published. Recently I have worked up the 208 AMAX, 190 Hornady BTSP, 180 Nolser ballistic tip. I found the 208 in my 300 RUM was .671. The 190 BTSP was .530 and the 180 BT was .524, yet it always "seems" to work out differently when matching real drops to the scope. However, I dont care. I use the drop data to figure my shots and I do NOT use data figured from double chronies due to these issues. Granted, I may not get an accurate picture as far as downrange impact velocities etc....This is why I also derive info from double chronies.
Now for a success story.
In 2002, I spent a couple weeks getting ready for a sheep hunt. I just got a new 308 and NF BR scope. Being somewhat new, I was using .125" for a click value instead of .125 MOA. Never the less, I went out and performed the drop tests. I would adjust my scope until I found the middle of the target. At 800 yards I was at 174 clicks. So in my mind it was 174" of drop. I played with the calculator and adjusted my BC untill my drops matched my data. This worked out to .484 using the 168 SMK. The reality was that later I found out I was wrong and my real BC was actually .450. Never the less, I was using "wrong" data and still killed a ram at 763 yards with ONE bullet. I was still using numbers based on real world tests, albiet one factor was wrong, it was washed out. YOU CAN ETHICALLY KILL GAME OUT TO 1K USING THIS METHOD!
In my case, that old BR scope was really .125 MOA. The error lied with me and not the scope. However the error was still hidden in the BC. A dead ram was the result.
Now if you want to get technical, you can test you scope values by cranking the dial and shooting at 100 yards. The target MUST be exactally 100 yards from your scope. You can find the real MOA or inch value per click using this method. By using this method, double chrony tested BC's are much more accurate when plugged into the software. For me, I have shot enough to know that things arent always what they should be. This is why I still advocate finding values from drop tests, at the very least, verifying them. The funny thing is that after "verifying" and things are off, I end up adjusting my BC anyway.
I said it once, I will say it again. Find your numbers via drop tests, use those numbers and be happy!
Also, to be fair to RR, I have seen different values based on double chronies with the same bullets but using different guns. You cannot predict with 100% ACCURACY a BC based on form factors or computer models. You can get close but and you can even find a darn good average. But you cannot buy into the thought that they will be the same from gun to gun.
This is a very good topic and really highlights the importance of gathering BC data from more than one type of test as well as the importance of regular practice and verification sessions. You cannot get an accurate picture of what is going on in one or even two sessions. Thanks RR!