Has anyone noticed a difference in avg fps when comparing virgin brass to once fired brass? I am seeing the following:
RL-16, Lapua 6.5 Creedmoor Brass, FGMM Small Primers, 140 gr Berger Hybrids
38.6, Virgin 2594 (Density Altitude 1514, Temp 80 F), Once Fired 2653 (DA 1211 , T 76) : 59 ft/s difference : 4 degrees difference
39.0, Virgin 2623 (DA 1750, T 85), Once Fired 2661 (DA 1277, T 77) : 38 ft/s Difference : 8 degrees difference
39.4, Virgin 2648 (DA 1647, T 85), Once Fired 2685 (DA 1281, T 77) : 37 ft/s Difference : 8 degrees difference
39.8, Virgin 2675 (DA 1880, T 87), Once Fired 2710 (DA 1308, T 79) : 35 ft/s Difference : 8 degrees difference
40.2, Virgin 2708 (DA 1904, T 87), Once Fired 2734 (DA 1480, T 80) : 26 ft/s Difference : 7 degrees difference
40.6, Virgin 2733 (DA 1948, T 86), Once Fired 2757 (DA 1522, T 81) : 24 ft/s Difference : 5 degrees difference
41.0, Virgin 2757 (DA 1958, T 88), Once Fired 2785 (DA 1640, T 82) : 28 ft/s Difference : 6 degrees difference
41.4, Virgin 2787 (DA 1938, T 88), Once Fired 2802 (DA 1675, T 83) : 15 ft/s Difference : 5 degrees difference
41.8, Virgin 2817 (DA 2012, T 89), Once Fired 2829 (DA 1778, T 85) : 12 ft/s Difference : 4 degrees difference
42.2, Virgin 2848 (DA 2002, T 89), Once Fired 2860 (DA 1820, T 85) : 12 ft/s Difference : 4 degrees difference
So some questions:
Does density altitude effect muzzle velocity by any measurable amount?
Wouldn't higher density altitude decrease the air resistance in the barrel and create higher muzzle velocity? In this example it appears that the lower air resistance (Higher DA) and higher air temps produce lower muzzle velocities, which is the opposite of what I thought would happen.
If it is a difference between virgin and fire formed, wouldn't the fire formed brass have a higher internal volume and would have lower pressures?
Aside from the first set of values (38.6 Virgin Brass was fired from a cold clean barrel, 38.6 fire formed was from a cold barrel), we can see that the difference in ft/s is lower when the difference in temperature and density altitude decreases. RL-16 is supposed to be temperature insensitive powder, does this small of a difference in DA and Temp effect the muzzle velocity by that much?
RL-16, Lapua 6.5 Creedmoor Brass, FGMM Small Primers, 140 gr Berger Hybrids
38.6, Virgin 2594 (Density Altitude 1514, Temp 80 F), Once Fired 2653 (DA 1211 , T 76) : 59 ft/s difference : 4 degrees difference
39.0, Virgin 2623 (DA 1750, T 85), Once Fired 2661 (DA 1277, T 77) : 38 ft/s Difference : 8 degrees difference
39.4, Virgin 2648 (DA 1647, T 85), Once Fired 2685 (DA 1281, T 77) : 37 ft/s Difference : 8 degrees difference
39.8, Virgin 2675 (DA 1880, T 87), Once Fired 2710 (DA 1308, T 79) : 35 ft/s Difference : 8 degrees difference
40.2, Virgin 2708 (DA 1904, T 87), Once Fired 2734 (DA 1480, T 80) : 26 ft/s Difference : 7 degrees difference
40.6, Virgin 2733 (DA 1948, T 86), Once Fired 2757 (DA 1522, T 81) : 24 ft/s Difference : 5 degrees difference
41.0, Virgin 2757 (DA 1958, T 88), Once Fired 2785 (DA 1640, T 82) : 28 ft/s Difference : 6 degrees difference
41.4, Virgin 2787 (DA 1938, T 88), Once Fired 2802 (DA 1675, T 83) : 15 ft/s Difference : 5 degrees difference
41.8, Virgin 2817 (DA 2012, T 89), Once Fired 2829 (DA 1778, T 85) : 12 ft/s Difference : 4 degrees difference
42.2, Virgin 2848 (DA 2002, T 89), Once Fired 2860 (DA 1820, T 85) : 12 ft/s Difference : 4 degrees difference
So some questions:
Does density altitude effect muzzle velocity by any measurable amount?
Wouldn't higher density altitude decrease the air resistance in the barrel and create higher muzzle velocity? In this example it appears that the lower air resistance (Higher DA) and higher air temps produce lower muzzle velocities, which is the opposite of what I thought would happen.
If it is a difference between virgin and fire formed, wouldn't the fire formed brass have a higher internal volume and would have lower pressures?
Aside from the first set of values (38.6 Virgin Brass was fired from a cold clean barrel, 38.6 fire formed was from a cold barrel), we can see that the difference in ft/s is lower when the difference in temperature and density altitude decreases. RL-16 is supposed to be temperature insensitive powder, does this small of a difference in DA and Temp effect the muzzle velocity by that much?
