Always glad to help. That's what this forum is for.
:If this happens again, try laying the end of the ramrod across the ball, sitting on top of the muzzle, and smack it with the heal of your hand to push the ball flush with the end of the barrel. Be carfeull you don't break the rod. That's how I loaded some tight ctgs. in my 14bore rifle. You can also choke right up on the rod, only an inch or so sticking below your hand, and push straight done. It will resist, then of a sudden, the ball will move as the pressure increases. This is how I had to load the tight fitting combo for the deep grouve .45 I had when I lost the starter.
: Colerain also makes a 20 bore that's choked - for shot only. It has a .580 bore at the muzzle, for .040" choke. As you can load the .600's your's isn't one of those. As he makes .62 rifles, with a .620 bore, your's will also be a .620" bore. A pure lead ball should allow up to .015" patch or so. A WW ball, will need a .009 to .011 patch.
Your accuracy with naked ball seems quite good! The problem is fouling with naked balls. you could roll them in lube, like #1000 stuff & that will help and is how we lubed the .650 RB's for the Ferguson, breechloading flint rifle.
Daryl