Thread: Advice please

Originally Posted by Hunterdave

Velocity is 2820 fps, when looking at book data wouldn’t that be for sammi spec OAL?

Greetings @ Hunterdave,
The Hodgdon data loads have the 162 grain Hornady BTSP at 2.97 inches or 75.4mm which is longer than SAAMI max, Some years ago John Barsness came up with some rules including one on the relationship between case capacity and velocity using printed hand load data. He later validated them with his own chronographing. The rule is that possible velocity increases by one quarter of case capacity as a percentage. I have used the rule when sorting out appropriate loads fo my 6.5 and it works well. The additional case capacity for your LOA of 79.1mm over the Hornady load calculates to 2.2 grains or 3.6% bases on the Nosler case capacity adjusted for the longer Hornady LOA or 0.9% increase in velocity. This works out to 25 fps or 2,872 fps in a 24 inch barrel. With your 20 inch barrel this would drop to about 2,770 max velocity. I note that Nosler lists a max of 51.5 grains of H4350 (AR2209 in a different bottle) for the 160 grain Accubond. People often claim huge increases in velocity for seating the projectile out for added capacity but this is at the expense of higher pressures. In short your powder is hotter than that used in the Hodgdon Data, as verified by my own chronographing with my 6.5, and your load needs to be reduced. Please ask any questions you might have Forum or PM.
Regards Grandpamac.