That is a patched round ball twist. "The experts say" it is not enough twist to stabilize a conical bullet. Thus the bullet will start to tumble and accuracy will be lost.
A 1 in 10 twist is recomended for bullets. Some mfgs were making Hawken style guns with a 1 in 24 twist that were supposedly combos that shot both well. I have a TC Hawken I built from a kit that has the 1 in 24 and I shoot both round balls and conicals out of it. Workes just fine.
Best thing to do is get the gun and try it. Different powder measurments and ranges. Could be it will work just fine and the "exberts" be darned.
There are still some who insist a scope is not needed for the type hunting they do, ignoring the advances of the last 150 years in optical sights. (Even the ultra-conservative US Army has adopted optical sights.) The idea that in some special circumstances open iron sights or aperture (peep) sights might be more useful is not lost on me, but with the inevitable advance of age comes the reduction in visual acuity needed for using iron sights.
I believe that many who completely resist the idea of...