View Single Post
Old April 11, 2013, 11:27 AM   #20
Brian Pfleuger
Moderator Emeritus
 
Join Date: June 25, 2008
Location: Austin, CO
Posts: 19,578
Quote:
Originally Posted by Bart B.
Brian, why would the most accurate ballistics calculators drastically over-estimate the effect of wind at relatively close distances?

Doesn't a given bullet traveling 1300 fps a thousand yards down range have the same drift at 1100 yards further as well as leaving the muzzle at 1300 fps and its drift at 100 yards?
Bart,

I don't completely understand what you're asking but I'll try to clarify.

I should have qualified my statements a bit more.

First, I've really only verified the calculators with small-caliber cartridges, mainly .204 and .22-250.

Second, the way I wrote it seems to indicate close-range only and not long-range. I assume the calculators would be wrong at long-range too, I just don't shoot far enough to know.

Third, if it were just wind drift, I'd say it was entirely the fault of the shooter not knowing the wind but it's not. I found the drop calculations to be significantly pessimistic too, and the G7 drag functions are much closer to reality even for bullets that aren't supposed to be G7 drag. The G7 function tends to be slightly optimistic instead of pessimistic but it's a lot closer. The distance is a whole lot easier to get right, obviously, with laser range finders and whatnot, so I know it's not shooter error.

For instance, using a .204 32gr V-Max at 4,050fps and with all weather parameters entered, JBM Ballistics thinks that a 2" vital zone MPBR zero will be 260 yards and 2.1 inches low at 300, 6 inches low at 350 and 11.3" low at 400.

If I sight-in at 100 as it suggests, 1.5" high, I find that the 350 yard POI is no more than 3" low and the true MPBR, that it predicts at 298 yards, is closer to 320 yards.

There aren't any major shooter input errors. The MV is chronographed and the guns shoot reliable enough groups to know the POI reasonably. Weather conditions are taken from stations with a few miles and close enough to not matter any significant amount. Shooting multiple guns, in multiple places, multiple shooters and years worth of hunting. The calculators are consistently pessimistic.
__________________
Nobody plans to screw up their lives...
...they just don't plan not to.
-Andy Stanley
Brian Pfleuger is offline  
 
Page generated in 0.03944 seconds with 8 queries