I know this thread is a little over 4 years past. I found it while looking for others load data for the several different variants of the .338-.300 Win Mag. I just ordered a .338-.300 Win Mag reamer from JGS. Went with a 35 degree shoulder, minimum neck “No turn”, had the reamer set up for the 230gr Hornady ELD-X’s to be .010 off the lands at a COAL of 3.550 in Winchester brass, so they will feed from a Magpul AICS Mag.
I thought what the heck. I own a .338 Ultra and a Benchmark built .338 Edge which is spooky accurate. I also am very fond of the .300 Win Mag chambering. I built a 28” 7mm-.300 Win Mag this last fall and it surpassed my expectations in performance and accuracy. I took a Mulie with it this last fall at 847 yards.
So I already have plenty of .338 bullets in stock along with .300 Win Mag Brass.
Way cool. I’m looking forward to seeing what your velocities are going to be with the improved shoulder. Once you fire form and work up full house loads. Your going to be nipping at Lapua velocities. With way less powder.