This is the Hodgdon data for the 500gr Hornady SP with Lil'Gun again, with an 8" barrel. To me, it's consistent with both the Hornady data, and the Quickload projections:
2.065" OAL
27.0 grs
1356 fps
41,700 PSI
30.0 grs
1463 fps
50,100 PSI
The above does not seem to differ greatly from the Quickload data, as you have to factor in the shorter OAL (2.065" vs. 2.300") which increases pressure (and MV) quite a bit, and the much shorter barrel (8" vs. 22") which decreases the MV by probably 200+ fps (15+ fps/in).
Quickload is a software simulator that is very good at estimating, but it's an estimate, and you have to compare apples to apples, as seemingly small factors can effect large changes. Even with published load data, each gun, powder lot, bullet and shooting temperature is unique, so tables are only good estimates for pressure and MV.