You can determine the OAL by examining the design of the bullet. Start long. How much "flat" area is left above brass at 2.260? If significant, then you can go deeper, etc. The limit of how deep you can go is you dont want the brass to go even .001 past where the bullet starts to taper. The brass neck must "all" be on the flat part of the bullet. If it is on the flat part of the bullet, OAL within reason, is just preference. Bullets with can. or those channels cut into them, are for crimp, and for those, you want the end of the brass to be inside the can. area. That dictates OAL.
I seat almost everything at 2.255. The reason why you don't want to seat a few at 2.260, if the magazine tolerance is say..."near that" is because you could get some bullets with longer tips and then hurt your reliability because they will be touching the magazine and not feed correctly.
Factory OAL means almost nothing. OAL determines pressure, and is just "1 point" at which the brass neck is sure to be on the flat part of the bullet. In reality, if a bullet is seated at 2.200 or even 2.185, then it will take 2.255 no issue. However, bullets that are designed for longer OAL, such as 2.250, cannot take 2.200 because its possible the brass will go past the flat into the taper, etc.
I hope this helps.