the 452630 is a lead semi wad cutter with a beveled base, pretty popular and has been around since about 1950. I saw the max load for bullseye being 6 grains which might be a bit hot for some pistols. As with anything else, I would begin at the starting load and work up for best performance. For a heavier than target load in my 1911s I use 5.3 grains of Bullseye. I don't have access to a chronograph but it works well and hits pretty hard. But then I was more interested in accuracy with a higher powder charge than I was pure velocity.
Lyman's data has served me pretty well over the years, and I have also used Midway USA Load map for data, along with various powder makers recommendations.
Anything you change from what their particular manual states can change pressures, something to be mindful of, especially at the higher loadings. Things such as cases, which may have a smaller case capacity than what was tested, primers, cartridge overall length and bullet design all play a factor.
Also, I notice that Alliant's on line load data does not mention pressure. I wont say that its listing is max but Speer does mention the load for a similar bullet is not max and is for target loads. Lyman lists a higher powder charge but also lists pressures which is informative.
As to the difference in loadings for the Lyman book, there is a noticeable difference in the bullet style. The 452460 is not beveled and contains 2 grease grooves where the 452630 has a single groove. I would guess the difference is going to be in the bearing surface, or how much of the bullet touches the rifling, plus notice the seating depth. The 452460 is seated significantly deeper into the case which raises pressure. My personal load for the 452630 bullets are seated at 1.250 inches, longer than book spec, but they feed better in my pistols.
