Judging form those measurements, Lyle, they probably are from issue buck and ball ctgs. for the .69 muskets commonly used by US military up to about 1850- maybe even later in the 'open range'. There would be some expansion, which shows up in the slightly larger size from the nominal .640" and .650". the .64-0's were usually cast, I believe with the .650's being swaged- which would explain the tiny belt. Those with the belt must be .650's originally.
What animal - native men, women and children - mostly the men were the normal recipients of those loads. They were much more popular than normal single ball loads at about 4 to 1 ratio being used - 1800 through into 1850's and into the civil war as well. By 1850, most of the .69's that were in good enough shape, were rifled for the hollow based Minnie ball, although most forts kept a few muskets of earlier patterns for guard duty, etc.
Buck and ball is quite effective and extends the 'wounding' range of a musket to an easy 100 yards - generally. The 'early' charge of powder was 165gr. minus the priming taken from it and after 1820, the powder quality improved and only 130gr. was used. I find this interesting in light of the charges most 'guys' use today
. For the .69's there was no 'light' charge, so the very lightweight Carbine Sapper's guns also fired the 165gr. and 130gr. charges. Some complained of recoil.
The tri-imprints are from the big ball accelerating before the buck, which sits on top of the big one. Now, if you could have those little dimples all over the ball, in a regular pattern, the musket ball would have been more accurate. As it was, there dimples certainly wouldn't help and would probably start a spin earlier in flight to produce less accuracy of the big ball, than a single ball load - speculation only.