Sorry that I was a bit slow getting time to sit down and run through the numbers. Here's what I calculated
The 41mag 210 deep curl with a 1580mv and 1250 100y vel has a BC of 0.183 which is pretty good for a pistol bullet
Hornady calculator predicts 1270fps @100y vs the 1250 you measured.

the 240gn 0.452 CEB doesn't have a listed BC, but I used the 250gn Barnes bullet (0.141) with your 1620mv and calculated 1224fps @100y vs the 1190 you measured. If I drop the BC to 0.135 100y vel. is 1210. For comparison, the 240gn hornady XTP mag has a BC of 0.16 and would give 1262 @100y. If I gave the bullet a BC of 0.183 that matched your deep curl, the 100y vel. would be 1300fps which is the same as your 41 mag numbers as you would expect.

0.18 BC for a pistol bullet is pretty good. The 0.452 deep curl 250gn has a BC of 0.165. I think what you are seeing for velocities is just a difference in BC values. This is impacted by bullet shape and material. The 300gn Swift A-Frame in 453 has a 0.129 BC. The Lehigh 300gn match solids have a 0.21 BC (would give you a bit over 1300@100y).

Incidentally, CEB recommends a minimum terminal velocity of 1500fps for their FB 452 250 Cu RAPTOR (which they say is for the 450 bushmaster) to function as intended on impact. Have you tested it on any water jugs or other things at 100y to see how it performs?

FYI The Barnes 250gn has a 1050fps minimum recommended velocity. @ 1600fps mv you get ~1080fps at 150y.