Gremlin,fairies, pixies or demons riding on your balls...explains why so many looked grumpy at the last gun show I suppose... And, back in the day men used to think just having crabs was bad....
It all depends on the gun as to if the hook breech will affect accuracy or not. If you've got a good tight breech connection and positive consistent pressure on the wedge(s) with barrel mounted sights, likely there won't be any issues. If you've go a sloppy breech fit compounded with a sloppy barrel to channel fit, loose wedge(s) and a tang mounted sight, chances are good that it ain't gonna shoot for crap.
There's plenty of science to be put into blackpowder be it ML or BPCR, it all depends on how much or how little time and effort you wish to employ. Sorting balls by weight then checking them on a spin balance rig, using a compression meter to seat them, checking the weight of the powder lot you have against previous lots, velocity testing, patch material compression testing, re-screening powder and removing fines with an air curtain.... there are a great many things you can do if you wish. One thing that holds true to fact, the more effort you put into it and the higher the quality of the gun you use, the more you'll get out of it.
All things aside, there ain't nuttin' wrong with going out and plinking just for fun neither!