What started out a fun day of shooting turns out to firm up past observations and still a fun day. Consider 6800' elevation and 600 yards at paper target. A 6.5 x 47, 130 vld @ 3,000 fps. Also a 50 BMG, 647 Barnes TSX. Keep in mind I know very little about the 50 cal. The 647 bullet according to Barnes has a G1 BC OF .572 and the G1 BC of the 130 is .562 and this is where things get interesting. Both are shooting at 3,000 fps, so running the numbers illustrates a drift on both bullets of about 16 inches.
Firing at the same time after getting on target and fouling barrels, at 8:00 in the morning with absolutely no wind both bullets are about an inch left of X ring. Elevation of BMG is high 1 inch and 6.5 x 47 is low half inch. After firing two 3 shot groups all looks good. The 130 bullet has a 3 inch grouping and the BMG has a little over 6 inch grouping.
The weather report showed wind for the afternoon and it's decided to do a side by side later in day. Back to range and at 3:00 give or take a few min....sure enough 10-12 mph crosswind. Not knowing what to expect and knowing nothing about the 647 bullet, we simultaneously fired 3 shots each and the 130 moves an inch further than predicted ...17 inches. The BMG only moves about 12.5 inches....again measuring center of group to center of group. After firing one more 3 shot group we see the same thing. That is a difference of 4.5 inches which does not sound like much but would be around 13.5 difference at 1,000 yards.
The BC of the big bullet would need to be corrected substantially to get to these numbers and that would move the drop substantially. So, if the BC is correct, which I believe probably is by looking at the shape of the bullet, does this not illustrate that we have a bit more going on than just BC? Is this an anomaly? Realizing that as bullets more closer to the same weight you would never see a difference like this, but when comparing 6's to 30 cal's, I've witnessed similar results just not as drastic. At some point I hope our programs allow us to better evaluate windage of various combinations. I think all of our ballasticians who contribute to this site are phenomenally smart folks and help us in so many ways to understand these complicated issues, so in no way is this a jab at what we have to work with. This is just an observation that many have probably witnessed.
Very fun day....always learning....even at 68 and all the warts!
Firing at the same time after getting on target and fouling barrels, at 8:00 in the morning with absolutely no wind both bullets are about an inch left of X ring. Elevation of BMG is high 1 inch and 6.5 x 47 is low half inch. After firing two 3 shot groups all looks good. The 130 bullet has a 3 inch grouping and the BMG has a little over 6 inch grouping.
The weather report showed wind for the afternoon and it's decided to do a side by side later in day. Back to range and at 3:00 give or take a few min....sure enough 10-12 mph crosswind. Not knowing what to expect and knowing nothing about the 647 bullet, we simultaneously fired 3 shots each and the 130 moves an inch further than predicted ...17 inches. The BMG only moves about 12.5 inches....again measuring center of group to center of group. After firing one more 3 shot group we see the same thing. That is a difference of 4.5 inches which does not sound like much but would be around 13.5 difference at 1,000 yards.
The BC of the big bullet would need to be corrected substantially to get to these numbers and that would move the drop substantially. So, if the BC is correct, which I believe probably is by looking at the shape of the bullet, does this not illustrate that we have a bit more going on than just BC? Is this an anomaly? Realizing that as bullets more closer to the same weight you would never see a difference like this, but when comparing 6's to 30 cal's, I've witnessed similar results just not as drastic. At some point I hope our programs allow us to better evaluate windage of various combinations. I think all of our ballasticians who contribute to this site are phenomenally smart folks and help us in so many ways to understand these complicated issues, so in no way is this a jab at what we have to work with. This is just an observation that many have probably witnessed.
Very fun day....always learning....even at 68 and all the warts!
