Because of manufacturing tolerances and conservative manufacturers there is always a sizable gap between the end of the case neck and the end of the chamber. This can be as long as 0.045” with both the case and chamber in spec and longer if one or both are out of spec.
Lead and gunk collects in this gap in varying amounts. Is that a concern? Does it affect accuracy with cast bullets when this collection of lead and fouling varies over the course of several shots?
Some competitors think it may be one cause of those occasional fliers and they use longer brass to resize to a longer length than specified to shorten the gap (30-06 cases formed to 308 with a neck that almost reaches the end of the chamber's neck for instance.)
If this is over done the case mouth could be pinched down on the bullet by the end of the chamber and theoretically increase pressures so care is called for.
Has anybody done any testing to prove or disprove that the gap does any harm and thus it might be worthwhile to fit cases to shorten the gap -- or not?
John