Convert Berdan steel cases to Boxer

How I convert Berdan steel cases to boxer. I use a Guide to stay on center as I drill through the berdan primer and drill in just far enough to remove the anvil at the bottom of the primer pocket. This leaves a boxer sized whole in the bottom of the case. I then increase the size of my drill bit and expand the whole on the primer. The primer becomes a bushing for the larger .217 berdan pocket to allow a boxer .210 primer. I then swage the primer pocket. Once swagged I have a steel boxer case. I have not had any problems with the berdan bushing coming out when I reload. I fired around 30 rounds last week 10-13-14 with no movement on any of the primers.