Hodgdon says it is most similar in burn rate to H1000. I would use that data to compare velocities. IMR7828 is a denser pattern so I don't know of a formula to develop the weights. I would work up a load with H1000 with tested data and use that as a base line for velocity. I would start about 5-10% lower with 7977 and work up to a similar velocity as the H1000 load while watching for any indications of pressure such as a drop or flatline in velocity per half grain of powder.

You can compare the two in similar sized cases to get a rough approximation of the ratio. In the 7RM 7977 was running about 4% higher than H1000. I would knock that back to 3% as a fudge factor and work up accordingly multiplying known H1000 loads by 103%. Please report back so we know that you can still type.

"When you disarm the people, you commence to offend them and show that you distrust them either through cowardice or lack of confidence, and both of these opinions generate hatred." Niccolo Machiavelli