The .284 case is a very strong. I would go with the .284 Win. GAP match the reamer is available from Midway. You can seat a Sierra 175 Match King out to 3.100 oal. That's what it was designed for. I have had different rifles in 6mm,6.5,30 and several in 7mm. The .284 with a long barrel holds its own with the .280 Ackley . The 7mm bullet I use is the 168gr. Berger VLD Hunting style. I am getting a MV. of 2,950fps. From a 27 1/4" SS barrel. Buy the way my load is Reloder 17 a charge of 51.5 grs and a WLR primer. The COAL is 3.120".gun)