Originally Posted By: BeluebowOriginally Posted By: CatShooterOriginally Posted By: jeepnsammysok im sure lots of you are way beyond me so i ask you after developing your best hand load then collecting your fps and entering that along with all the other needed info to get a trajectory chart printed out whats the best way to correct the trajectory chart if its off? if you change the bullet b.c. that can help to align things or the fps but is there more ways? are these ways wrong? is there a correct way?
Tweak the BC, not the scope height or velocity.
The reason is that most BC's are not derived by a standard method, so they are close estimates anyway.
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Cat are Bryan Litz tested bullet bc's close to accurate? Seems to me if you start messing with bc numbers it will throw the wind drift numbers out of whack,,and we all know how humbling the wind can be,drops and velocity are alot easier to compensate for,,and the accuracy of chronographs leaves some (myself included) scratching their heads.
That is a good question... excellent in fact.
Lookie.. the whole reason for this BC stuff and ballistic programs is one thing - to predict (the best we can) where the bullet will hit.
All the numbers and software is very pretty, but it useless if it cannot tell you how much drop you have, and how much elevation you need to dial, to whack that woodchuck or PD out past the north 40.
Right now, we can get pretty good range data from lasers or high end optical rangefinders. You can literally come within a yard or two for range data, if you chose your tools properly.
Our wind data is iffy at best. If you have a Kestrel wind meter, and take the wind at your location - say it says 10mph - that means very little. You have a 10mph wind at 5 feet off the ground, but that crow is 565 yards away, across an open field, and you have no way of knowing what the wind will be. It might vary from 6 to 14 mph across that field.
So, we have one number that is solid, and a second number which is an estimate.
I'll use an example of a rifle that I am taking out of the mothballs. It is an old (like new) benchrest rifle in 222 Mag, that I bought in 1975 and campaigned for three years (and did well). I re-did the stock to a varmint contour stock and used it in the field for a year or so, and then it got stored. It has collected dust for a long time.
I recently re-scoped it with a 24x Leupold BR-D, and have a good working load with 50gr Sierra BK's. It shoots between 0.15" to 0.2" (most of the time).
Last fall, when I was checking the drop figures, I shot it at my club's 400 yd range, and measured the drop. With a MV of 3530, and a 100 zero, I had a drop of 21.5".
The Sierra Infinity program predicted 19.7".
That was a 2 inch error, and that was both surprising and disappointing, cuz the Sierra program is excellent with their own bullets, and it meant that I would have to do some fiddling, and test drop at all ranges I plannned to shoot - and that would be a pain in the butt.
Then I decided to ping the 400 yard target, and it came out to be 415 yards, and the predicted drop would be 21.55", so the actual drop was exactly what the program predicted, and I know I can use it to the limits in the field and be dead on.
Now to the reason for the above tale.
Sierra tests their bullets against their software, and "tweaks" the BC so it will match the real drop exactly. They might release a bullet for sale, and not have an accurate BC for it for a year or more after it is being sold, cuz it is still being tested
Now, Sierra is the only bullet company to do this - the rest just measure a velocity drop over 100 or 200 yards, and then use the 100 years old Ingle's tables to get a BC - and that BC is an approximation.
So, you can do what Sierra does - tweak the BC so it matches your software, so you can be dead on.
As far as wind... since our wind data is only an approximation in the first place, and we cannot get it any better, then it makes sense to optimize the most important data, and let the approximated data be a little loose, since it is already a little loose to begin with.
I don't know how Brian get's the BC's for Berger, so I can't say - but I did read a few things he wrote about bullet flight and it violates every law of physics known to man.
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