At 7000ft. altitude, 60degrees F, with some wind I shot a Harvester sabot with a 300gr. solid copper clad pistol bullet and the following resulted:
With 100gr. volume Black Mag'3 and a Winchester standard small rifle primer in the 25ACP conversion on my stainless Omega I recorded a three shot average velocity of 1920fps. I later shot the same load but changed to a Winchester standard 209 primer and the velocity average for three shots was 2004fps. Magkor confirmed that the velocity with the 209 primers should be slightly higher than with a standard small rifle primer or a #11 cap. The same volume of 777 ffg and the same bullet only hit just under 1700fps. (I have a person that claims my numbers for the 777 are not correct but that is what I recorded and have no reason to disbelieve my chronograph as it is just back from the manufacturer and has been completely rebuilt). 777 in my Omega is a mess to deal with and the crud ring is very heavy and difficult to remove. I shot the three shots with Black Mag'3 without a swab between shots and the loading was not difficult.