Mikecr
Well-Known Member
From QT Sierra 240mk G1 BC is .699 under ICAO conditions from 2150fps
My math would predict .703 from measurements given to me, same conditions.
Now this is based on a calculated uniform specific gravity of 10.3, an OAL of 1.600", a meplat of .062, and a .760" nose with a 7.8cal tangent radius ogive.
A good enough twist for this at ICAO would be 9.5
If I drop USG to 8.9, changing only length to make 240gr weight, ICAO/G1BC = .695 and same performing twist would be 7.5
So BC would be lower and twist reqs go tighter...
If I change no dimension, weight goes to 208gr, BC to .608, twist to 8.5
I doubt there is any gain here...
Note, this 8.9 specific gravity, assumes copper only, and not a poor performing alloy I suspect Lost River may have used(if more brass-ish USG would drop toward 8.2)
But a turned bullet would likely be enhanced with a smaller meplat;
If I drop the meplat to .030" and lengthen as before for a 240gr copper SMK, I get a BC of .723 with 7.5 still a good twist.
If I use this meplat in the lighter bullet example(208gr), BC would be .634 and a good twist is still 8.5
So I conclude there is potential(if we ran out of lead), but not much, and who knows how well it would shoot...
My math would predict .703 from measurements given to me, same conditions.
Now this is based on a calculated uniform specific gravity of 10.3, an OAL of 1.600", a meplat of .062, and a .760" nose with a 7.8cal tangent radius ogive.
A good enough twist for this at ICAO would be 9.5
If I drop USG to 8.9, changing only length to make 240gr weight, ICAO/G1BC = .695 and same performing twist would be 7.5
So BC would be lower and twist reqs go tighter...
If I change no dimension, weight goes to 208gr, BC to .608, twist to 8.5
I doubt there is any gain here...
Note, this 8.9 specific gravity, assumes copper only, and not a poor performing alloy I suspect Lost River may have used(if more brass-ish USG would drop toward 8.2)
But a turned bullet would likely be enhanced with a smaller meplat;
If I drop the meplat to .030" and lengthen as before for a 240gr copper SMK, I get a BC of .723 with 7.5 still a good twist.
If I use this meplat in the lighter bullet example(208gr), BC would be .634 and a good twist is still 8.5
So I conclude there is potential(if we ran out of lead), but not much, and who knows how well it would shoot...