Hi, The first thing I would do is get your load chronographed over at least 5 shots and the more the better. I did a little checking and Hodgdon's data shows that you would be getting about 2850 FPS or maybe a little more. THe thing is you can't just go by what the book says. You can mess around with a calculator and the two known distances, drops and play with the numbers to find out what your velocity is... but it's a pain. Go to JBM - Calculations - Trajectory Enter in your velocity for 2850 and the 0.648 BC and you will be very close to what your field varifications were 2950 really sounds a little high for that bullet. I'm shooting a wsm and Pushing the thing pretty hard from a 24" barrel getting 2950 from the muzzle w/ 180 grain bullets. The win mag has a little more torque but not that much.
Also, I would start off by shooting at 200, 600, and 900 without moving the scope and shoot 5 rd groups at each. Measure in inches what the actual drop was. This will give you a very good measurement of the true BC of your bullet, or tell you if your measured velocity is accurate.
I used to re-load but now I "hand-load".
-- Well, at least I try --
Location: The rifle range, or archery range or behind the computer in Alaska
Re: Help with trajectory please "thing"
1: If youre using a second focal plane variable power scope, I would verify that you were on the appropriate setting.
2: See if you can duplicate your reults.
3: Verify your velocity. You are likely to be less than you expect.
4: You mentioned low humidity. Humidity has very little effect on a bullet. The difference between 0% and 100% is very minute even at 1K yards. You mentioned nothing of pressure. Barometric pressure even in small changes have a very drastic effect on bullet trajectory. Find an accurate pressure. This will help you find your true numbers.
5: Have you tried different drag functions?? This is most likely your issue. Try G5 and G7 over G1. One of these will likely get you closer. I use my own personaly developed software that allows me to make the drag function any number I wish. Between adjusting the drag function and BC I can match ANY real world trajectory to within an inch at any point in the range.
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.
Last edited by Michael Eichele; 03-14-2009 at 03:52 AM.
scope is a FFP scope and so far its proven to track very well. distances are assumed from a palma range, we verified the 900yds via GPS also. I shot over 50 rounds to get these numbers, not just a few.
but not to worry, i seem to have gotten closer since my last post.
from this data, closest i can make fit is this...
2950fps, .62 BC
zero at 218yds. (1 inch groups centered at 218yds)
3.0 mils at 600, (i measured 3.1mils actual)
5.8mils at 900 (same as i measured)
only thing i can figure is that my 600yd drop is maybe 0.1 mil error???
does this sound ok?
i worked this out via trial and error using the "thing", is there a more methodical way other than subbing in random values to get a traj close to what you measure as actual???
Also as a side note, i needed 0.3mil left at 900 also, i didnt think spin drift would be that much, is it possible or somthing else???
I measured the G1 BC of the 208 Amax to be 0.633 (average value from 3000 to 1500 fps) and the G7 BC is 0.324 (valid for all speeds).
Using this BC, you're velocity would have to come down from 2950 to match your trajectory.
You asked about a more 'methodical' way. The first step is to measure your muzzle velocity.
You can expect about 5" of spin drift with the 208 Amax at 900 yards from a 1:10" twist barrel.