Frustrating day at the range, advice welcome

Had a near perfect day at the range yesterday, not too hot, no wind, good light. Shot 40 rounds left over from two batches made before Glastonbury and Middletown. Of those 40 rounds, 7 keyholed. Bottom pic is a benchrest 50 yard 6 shot group. Very first shot with a clean bore keyholed into the frame off the paper. Middle pic is my best offhand 6 shot group at 50yards (1 shot keyholed off the paper). Top photo shows two keyholes that found paper (I particularly like the left keyhole showing a perfect profile of the Hodgdon bullet including grease grooves).

I'm pretty sure the bullet is sized correctly ( I even bought the next size up sizer, .577, to try it, doesn't fit). I'm also pretty sure the lead is pure or near pure. I don't have the ability to measure hardness, but I can easily dent the bullets with a fingernail. I weigh each bullet to eliminate voids in the casts, and use a sizing die on each round.

I have two theories, any input appreciated. First, I'm deforming the nose of the bullet during sizing or loading. There were a few early rounds that took a little extra effort to load. It actually got easier to load after those 4-5 shots that came early in the shooting cycle. Keyholes appeared randomly throughout, though, even with rounds that required only the normal effort. The lyman sizing die does leave an indentation on the nose in the sizing precess. Perhaps its making some of the noses slightly off center? Or I am during the loading process?

The second theory is problems with the barrel, either leading or the crown. I bought the barrel used last Fall, and have no idea of its history. James River Armory told me it was only slightly uses, and had been sitting around the shop, dirty with some light surface rust. The crown is a little rough, looks like it was rough filed, but does not have any dents or dings. Any ideas on where I could have it examined? I'm thinking of taking it to Bobby Hoyt after the Fall Nationals, but don't want to waste his time if its unlikely the barrel is the issue.

I'm going to try to carefully make another 100 rounds before the next Middletown skirmish, and see if I can't eliminate the keyholing in the manufacturing process. My process is as follows: Cast bullets, and cull any casting flaws, particularly problems with skirts. Cull again by weight to eliminate voids. Load powder charges into clean cap plugs, and seat bullet nose down into capplug, leaving the grease grooves showing. The bullets are then dipped into Walts formula bullet lube, covering the base. I have the finished rounds stored in an airtight case. Any recommendations or things to look for appreciated.

My goal by the end of the season is to have the musket and ammo squared away, and be able to work on my form next season.