The shape of the bullet has a lot to do with seating depth, especially if the bullets like to be seated close to the rifling. Some bullets seem to like to be jammed. I've been told by a gunsmith who turns out some pretty accurate rifles that if the leade angle is steep that seating the bullets back from the rifling frequently helps accuracy.
The shape of the ogive of the bullets makes a difference in where bullets can or should be seated if the barrel likes to have bullets seated close to the rifling especially, i.e., just touching or 0.005" to 0.010" say.
It seems that nobody wants to do the experimental part of working up a good load. Nobody can give someone the best load for their rifle, or tell them where a bullet should be seated. The best advice is to choose a bullet for the shooting that is to be done with the rifle, most modern bullets are plenty accurate for what they're designed to do so unless you're shooting BR bullet's not much of a problem. If the load is to be used from a magazine the rounds have to be seated to feed from the rifle's magazine. If you're not feeding from the rifle's magazine or it's a single shot, start with the bullets at the rifling, and load three rounds with each charge up to a manual or other published maximum (from a respected source, not a load from some guy on some forum who you don't know from Adam's off ox), starting 5 or 10% below the max charge. Fire those from lightest to heaviest charge looking for excessive pressure signs and chronographing them. The velocity increases per charge increment should be more or less the same unless the starting charge is very low. Try several powders of interest in the same fashion. Measure your targets and retry the loads that look the most promising, but firing five shot groups or three shot groups with each load (depending on recoil or?), swabbing out the bore with two or three wet patches and a couple of dry patches at each change of powder (depending on how much fouling your barrel collects, but this is the minimum needed between powders IMHO). With any luck you'll find a good load or at least a satisfactory load for your purposes without shooting out a barrel. When you've found a load that looks good load a series of rounds with everything the same but seating depth. Start again at the rifling, then 0.010" deeper to 0.030 or so deeper. Three rounds at each seating depth should be enough to give you an idea what the rifle likes best. If you find that one seating depth seems best then try some more at that seating depth.
It's not necessary to try every bullet or every powder or ever primer, just choose a bullet that seems like it'll do what you need, a few powders that seem to be good for the caliber. Once you've got a good load then you can try other bullets or primers if you want.
