If you plan to shoot the 105 hybrids you will need a longer throat than the .104, i use the .135 FB. and it works with the 105H Spencer 103 and the 104 BIB. I'm sure you will hear a lot different answers, but think about it........ jim
My guns have a .266 neck and I like it. Cases clean up nice. I would think a .268 would work good too and might give a little more hold on bullet for jamming into lands. Matt