Peter and HHorse - I am referring to the issued U.S. military ctgs. issued for their .69 cal muskets. I am not suggesting anyone use these loads, this is merely a history lesson.
You are right in that 000 will not lay properly in a .690" 'calibre' of the issue US musket, but that is what they used - and to good effect as they noted, 'prowling wolves' around the fort at night rent out shrieks of pain when struck by the buckshot loads, yet no bodies were evident in the morning's search. These 'wolves' they spoke of were, of course, Indians checking out the fort's night-time defenses.
Many troops complained about the recoil of issue buck and ball (3- TRIPLE OUGHT + ONE .64" BALL) and ball loads - of course. They also had difficulty with some of the breechloading guns as the issue ctg. held more powder than would fit into their chambers - primarily the Hall carbines in ".64 calibre which would shoot the issue ball of .64" - so at that time, 1830'S, the issue musket ctg. ball's diameter had not been increased to .65" - yet - yet was increased in time to be used in the .69 cal percussion musket of 1842 & in all those which preceded 1842 that were still in use.
As a further note, these 1842's along with other issue muskets of decent remaining barrel thickness were returned to Harper's Ferry and Springfield for rifling during the 1850's, after the invention of the thin skirted hollow based Minnie Ball. At that time, the issue load for the .69 cal rifled muskets was 70gr. for the 730gr. Conical Ball. The .58's, of course, rifles only, (not rifled muskets as there were never any .58 calibre muskets) used 60gr. with the 505gr. while the .58 pistols used a mere 50gr. with the 460gr. reduced weight Minnie ball. Lyman used to sell the lighter pistol bullet mould as the #575213OS- iirc. I believe the OS to them meant "original style". They certainly were not over size as they cast .575" as they should. They also made a #585213 mould to cast a larger "Minnie ball" for the Snider, ctg. rifles.