I don't know the "strength" of the Henry, 2200fps with a 300gr is 100fps above what my book lists for the 1895 Marlin, and almost over 300fps faster than the old listed loads for the 1886 Winchester.
This is a 22" barrel, mind you, and like I said I was getting about 1900 fps. The "formula" came out of western powder's guide for "modern" 45-70's.
Just checked--here the actual labradar numbers:
300 HP 62.2 Xterminator
Series No 6
Total number of shots 4
Units velocity fps
Units distances yd
Units kinetic energy ft-lbf
Units weight grain (gr)
Stats - Average 1907.46 fps
Stats - Highest 1931.01 fps
Stats - Lowest 1861.47 fps
Stats - Ext. Spread 69.54 fps
Stats - Std. Dev 32.37 fps
Shot ID V0 V25 V50 V75 V100 Ke0 Ke25 Ke50 Ke75 Ke100 PF25 Proj. Weight Date Time
1 1931 1822 1719 1623 1527 2483 2210 1967 1753 1553 546.6 300 01-19-2019 03:25:12
2 1929 1820 1717 1621 1525 2478 2205 1963 1750 1548 546 300 01-19-2019 03:27:26
3 1861 1757 1657 1565 0 2307 2056 1829 1631 0 527.1 300 01-19-2019 03:28:48
4 1908 1800 1698 1603 1508 2424 2158 1921 1711 1515 540 300 01-19-2019 03:30:38