Shorter threads on the "commercial" nipple will allow more 'space' under the nipple.
The rifle's crown has sharp edges/corners. They need to be smoothed.
A radiused crown, like I showed on my .32, is the proper 'angle' for drawing metal(lead).
A coned muzzle is not the proper angle and actually increases friction making it harder - yes- harder to load tight combinations.
Use the short starter to start,t hen punch the patched ball down into the bore. Once the ball and patch are into the bore, they
are now the size of the groove to groove measurement. If the patch is substantial enough & wet with oil or liquid, there will be
zero fouling buildup, shot to shot.
My .32's muzzle, 2 pictures with different lighting. I was able to load .311" RB's with .022" patches, along with .320" RB's with the
same patches, and seat them into the muzzle just by pushing on the starter (with the nubben on the patched ball), no smacking
needed, however giving the starter a smack is easier on the rifle's wrist. My rifle had a 5/16" rod, tapered to slightly less then 1/4".