Probably the biggest factor controlling COL is the ogive shape and nose diameter and length of the bullet in question, lots of big cast bullets are smaller in the nose diameter to allow seating long, as for the jacketed bullets, this line up tells the story much better than words, you can see the difference in the comparison below, L to R, 300gr Speer, 300gr Rem, 405gr Rem, 400gr Speer FN, 350gr Speer FN, 350gr Hornady RN and 350gr Hornady FP Interlock. Just an FYI, Remington factory 405gr ammo has a COL of 2.538", well short of the 2.55" spec.
As for seating cast bullets into the lands, it doesn't create as high a pressure spike in start pressure as jacketed bullets do, just be sure to work the load up from start as opposed to just changing the seating depth of an existing load that you've been using. The quote below is from the Lyman Cast Bullet Handbook on seating depth for cast bullets:
Cast bullets, because they are "softer" (20BHN vs 100BHN) than jacketed bullets, suffer more from any free travel before rifling engagement. Seating the bullet to engrave from the rifling often improves accuracy. Try both techniques, even if the actual overall length exceeds that listed in our tables.
Tim
