I really like the program but found out something I considered unusual about Ballistic FTE. It uses a different convention for wind direction than any other official wind report I have ever used.
As a pilot I use wind reports all the time, and they are always issued issued as a bearing on the compass rose, referenced to the directions the wind is coming FROM. A wind reported as 090/10 would be coming from the east, blowing to the west, looking at a north up compass rose that is right to left. Every official wind report I have ever seen is referenced that way.
In ballisticFTE the wind is wind is input backwards from the normal convention...the 090 is the direction the wind is blowing TO, not FROM.
If you use the spin drift function, as I do, then this will cause a significant error in your wind correction- this happened to me last night.
I was shooting my .308 at an 11in wide target at 905 yards. I had a very small and steady 4 knot wind that was just shy of 1 oclock, call it 20 degrees from the right, mostly headwind but also generating a small right to left crosswind, which with a normal North up orientation I assumed (wrongly) would be input as bearing 020. Well, to Ballistic FTE, 020 is considered the heading of the wind so it was calculating a left correction for a left to right wind ...and adding the left correction for spin drift, (which is about 7in) to that for a total correction of 17inches, or about .5mil in the reticle. Now the correction was in green type, which I now realize implies a left hold, but I intuitively held into the right to left wind .5mil and of course I missed right.
I felt good breaking the shot, and with such light constant wind I couldn't figure out the miss. I corrected immediately using the reticle (easy to spot your own misses with a 308, especially when the TOF is 1.44 sec) and hit the target easily next round holding just a shade right of center.
Moral of the story, read the directions I guess.
That wind was very constant, and interesting because it was light enough and constant enough that for the first time I actually got to see the value of correcting for spin drift. The magnitude of the wind correction was about 10inches, or 0.3mil. The spin drift according to both Ballistic FTE and the equations in Bryan Litz's Applied Ballistics for Long Range Shooting is approximately 7 inches. Since spin drift is always right for a RH twist barrel the left 7 inches of spin correction offsets most of the 10 inches of right wind hold needed, resulting in a required hold of only 3 inches or 0.1mil of correction. Using <span style="font-style: italic">that</span> hold the next 6 rounds were good hits.
Considering the rifle is probably .8 moa at best at that range, and that without the 7inch spin drift correction the center of the group would be 5 inches off the edge of the target, it is likely I would have gotten several, if not all, misses without correcting for the spin. Since spin drift is a constant, to me it makes sense to go ahead and input the twist rate and bullet length and let the drift correction work in the background. Many days it will be lost in the noise of aim error, mirage, and wind estimation. Someday when you are really seeing the target and the wind is very steady or nearly calm then the correction comes out of the "noise" and will help you score more hits.
As long as you input the freakin wind direction into the program correctly!
As a pilot I use wind reports all the time, and they are always issued issued as a bearing on the compass rose, referenced to the directions the wind is coming FROM. A wind reported as 090/10 would be coming from the east, blowing to the west, looking at a north up compass rose that is right to left. Every official wind report I have ever seen is referenced that way.
In ballisticFTE the wind is wind is input backwards from the normal convention...the 090 is the direction the wind is blowing TO, not FROM.
If you use the spin drift function, as I do, then this will cause a significant error in your wind correction- this happened to me last night.
I was shooting my .308 at an 11in wide target at 905 yards. I had a very small and steady 4 knot wind that was just shy of 1 oclock, call it 20 degrees from the right, mostly headwind but also generating a small right to left crosswind, which with a normal North up orientation I assumed (wrongly) would be input as bearing 020. Well, to Ballistic FTE, 020 is considered the heading of the wind so it was calculating a left correction for a left to right wind ...and adding the left correction for spin drift, (which is about 7in) to that for a total correction of 17inches, or about .5mil in the reticle. Now the correction was in green type, which I now realize implies a left hold, but I intuitively held into the right to left wind .5mil and of course I missed right.
I felt good breaking the shot, and with such light constant wind I couldn't figure out the miss. I corrected immediately using the reticle (easy to spot your own misses with a 308, especially when the TOF is 1.44 sec) and hit the target easily next round holding just a shade right of center.
Moral of the story, read the directions I guess.
That wind was very constant, and interesting because it was light enough and constant enough that for the first time I actually got to see the value of correcting for spin drift. The magnitude of the wind correction was about 10inches, or 0.3mil. The spin drift according to both Ballistic FTE and the equations in Bryan Litz's Applied Ballistics for Long Range Shooting is approximately 7 inches. Since spin drift is always right for a RH twist barrel the left 7 inches of spin correction offsets most of the 10 inches of right wind hold needed, resulting in a required hold of only 3 inches or 0.1mil of correction. Using <span style="font-style: italic">that</span> hold the next 6 rounds were good hits.
Considering the rifle is probably .8 moa at best at that range, and that without the 7inch spin drift correction the center of the group would be 5 inches off the edge of the target, it is likely I would have gotten several, if not all, misses without correcting for the spin. Since spin drift is a constant, to me it makes sense to go ahead and input the twist rate and bullet length and let the drift correction work in the background. Many days it will be lost in the noise of aim error, mirage, and wind estimation. Someday when you are really seeing the target and the wind is very steady or nearly calm then the correction comes out of the "noise" and will help you score more hits.
As long as you input the freakin wind direction into the program correctly!
