The original purpose of the Kilburn chambering was to get a shoulder to headspace on. It works quite well in that regard.
Just remember to neck size only after the cases have been formed and don't push the shoulder back accidently ( easy to do )
I never had much problem with case loss in the forming stage, you will loose more cases by dropping them in tall grass than by splitting while fire-forming <BG>
Lay up some blackpowder and flints
The rest we can build, if need be