Does anyone make an inline with a 1:48 twist rate or a groove depth of .005 or greater? That may work. Most inlines, from what I have read, have twist rates of 1:28 and quicker and groove depths of .003" to .004".
I really do not believe you are going to be able to consistently, shoot round balls through an inline with a twist rate of 1:28 or faster. My understanding is the rifling is too quick and shallow. It may be possible to use a harder alloy. With a groove depth of about .003" - .004", and a thin RB patch of .010, the rifling may not engage the lead ball.
Try a hard alloy, a ball which is a few thousandths under the groove depth, a wool patch over the powder, a well lubed ball patch of .005 (I have never heard of one so thin) and a very low powder charge. This may work? There is absolutely nothing wrong with experimenting, as long as it is done safely. You don't want the ball so tight, it creates a barrel obstruction and acts as a barrel plug, so you effectively have a pipe bomb.
I am going to experiment with a conical in the shallow grooves, so perhaps we can share data from our investigations.
With the greatest respect, please see reply #16, a few places up on this thread. The two friends who conducted the inline experiment were both highly experienced ML shooters, and straight-talking, reliable people. If not for that, I would have had a hard time believing what their trial with roundball shooting in a fast twist, doubtless shallow-rifled inline barrel, showed. Yep, they could shoot accurately using patched roundball up to a 100 gr. by volume powder charge. I was amazed!
For shooters like this, they would have known to use a pure lead ball for maximum "grab" of the patch on the circumference of the ball, and to obtain obturation of the ball diameter as the power charge increased. They also selected a very strong patch material, "pocket drill", which is made to line pants-pockets and not give way from keys, pens, etc. in the pocket. Pocket drill is about .010 thick when compressed, as I recall.
In all truth, there is no way you are going to blow up a ML using a tightly patched ball, and indeed, long ago when barrels were significantly less strong, the loading method was to actually hammer the ball down the barrel! In another thread on this Forum, I explained about this, and how even a short-started ball is not going to blow it up either, tho anything atop the powder charge, such as a wad, can drive forward against such an item in the bore, an possibly create a "ring" in the bore there even tho the ball or bullet fires on out.
Of note: a round ball is the lightest possible projectile that can be used in a ML barrel with any accuracy at all, and because it has the least mass, it is also going to produce the least pressure from the firing of the powder. Further, a round ball has the least contact with the barrel, since only its perimeter as a single ring is contacting the lands and grooves. Hence it has the least friction in the barrel of any projectile, and again this means there is less pressure created by any given powder charge.
I do agree that an inline with deeper rifling should work better is shooting roundballs. Nonetheless, the 4H shooting with no more than 60 gr. powder, is likely to work, using a snugly patched pure lead ball, even in a 1:28 twist inline barrel. The usual caveat,
mark the ramrod, always applies!
Aloha, Ka'imiloa