You didn't say whether you have shot your under hammer rifle yet. If you haven't, what you will find is that when holding your rifle in the traditional manner with the supporting arm on the barrel or forestock you will often feel the sting of cap fragments hitting your supporting arm. It can be a bit unpleasant. What you need to do is to cover your supporting arm with a sleeve made of a heavy fabric such as denim. While a long shirt denim shirt or jacket may be a bit too warm in the summer, you can make a sleeve just to cover your supporting arm. I made one out of some canvas and put elastic in the upper arm to hold the sleeve in place. it works like a charm. However, I have since changed the way I hold my rifle. It is very light and can be held in the manner that I use. I place my supporting hand (my left hand) over my right hand in the same manner as a two handed hold on a handgun and place my left elbow against my side. I have found this hold to be even more stable than the traditional manner. If the rifle were as heavy or had as long a barrel as a traditional rifle, this kind of hold may not be workable but on my light H&A rifle, it is very easily doable, is very stable and keeps my forearm out of the way of cap fragments.