Well, a couple comments from the "Crusty Deary Ol'Coot"
#1. do follow the recommendations of good loading manuals.
#2. Be aware that trying to be safe by "overly reducing" starting loads can get you into big time trouble, a situation which is most likely to happen with the slower powders such as 4831 in a rifle or H110 in a hand gun.
If you read far enough, you will now find warnings to not reduce loads with the slower powders beyond a certain point/percentage, something which was never talked about in my early days of reloading.
#3. Bullet seating depth very likely can make make a difference in group size and/or point of impact.
One of the gun writers went to a considerable amount of effort a few years back to prove this point.
Rick's thought was that changing bullet seating depth would have an effect in changing barrel vibrations, very much like the use of the Browning BOSS. Thereby, changing the grouping ability of a given load and gun.
Now these bullet seating changes should be controlled and small and done in a recorded and repeatable series just as when "working up" a series of test loads, BUT probably done only after you have arrived at the best possible group and/or velocity by normal test loading and firing.
Once the best load is found, the small adjustments in bullet seating would be employed to hopefully find that load and barrels "sweet spot" in much the same way turning a Browning BOSS in or out would do.
In my very limited testing, I think Rick's thoughts may well have some value.
#4. Seating bullets deeper can, with some cases/powders/loads rapidly increase chamber pressures.
#5. Typically, heavier bullets in a handgun strike at a higher point of impact due to the increased barrel time (lower velocity) and recoil of that bullet.
AND #6. a couple years back, after shoulder surgery and with the possibility of being one armed for the coming hunting season, I found that a 5.5" Redhawk .44, firing 310gr. hardcast LBT bullets ahead of 19grs. of AA#9 at a vel. of about 1300fps, shot way high and hurt when fired one handed.
Well, BE SAFE and Keep em Coming!
CDOC