Shredder, that's right on large vs. small groups. The proof is firing 20, 30 or even 40 shot test groups. Note also that if a given load doesn't produce the same size groups all the time (within 10% extreme spread), you're not shooting enough shots per group to make them at least 90% represent the real accuracy of your stuff as you shoot it.
Your bullet's seated out too far when:
* the round won't fit in and load reliably from the magazine.
* bolt won't close easily on the round as it jambs into the rifling.
* it's not held good enough by the case neck to withstand normal handling and works loose from being seated to shallow.
US Navy Distinguished Marksman Badge 153
Former USA Palma Team Member
NRA High Power Long Range High Master
NRA Smallbore Prone Master