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Mines a marlin guide gun probably around 7.5 pounds. Haven't chronographed but taking into account its 18.5inch barrel should be around 1800fps.

Yep big hunks of lead do alot of damage! I see your load isn't too far off mine, I'm running 48.5grs of 2207 with the 400gr speers.

Nice one, 2207 has always been good for accuracy and velocity. I also use lee dies and have had no issues.

The factory 45-70 ammo is pretty slow only loaded to 28000psi SAAMI spec, since there are still a lot of trapdoor rifles around in the states. Real world velocities are in the range of 1600 - 1700fps...