Wookie, nice rifle. Do you like your scope that high? I guess I'm old school and like my scope as low as possible so I can actually have my cheek resting on the comb of the stock. My 264 shoots 140 gr Bergers at 3166 fps with 68 gr of Retumbo out of a 26 inch barrel and I might be able to squeeze a little more out of it if I try, since the primer pockets are still nice and tight after reloading them. I'm not sure you actually gain much by building a 6.5x300 WM over the standard 264 Win Mag, but to each his own I guess. The 6.5 STW seems way overbore to me and would be very hard on barrels, but if you just have to have one, go for it.
Many ask me about the scope height issue. If you met me in person you would understand. The stock is a 14 1/2" LOP & for the scope to give me instant visual when I shoulder it needs to be high. I had low mounts, but they were too unnatural for me. You have to use what works, & this works for me. Oh my cheek does touch the comb too!
This rifle started life as a 26" 264 Win Mag. For some reason I was getting hard extractions on once fired brass whether it was neck sized or F/L sized? I dropped my load way down. I started at 74gr H870 which was @ 3220 FPS, right where I wanted to be. But with tight extractions, that wasn't going to work. I dropped back all the way to 70gr H870 which put me in the 3000 FPS range & was still having problems? Didn't build a 264 WM to shoot 3000 FPS with a 140gr. My as well be shooting a 30/06 at that point.
Took it back to the gunsmith, he figured it was brass, but I tried 3 different kinds of brass. Rem, Win & Nosler, results all very similar. He pulled the barrel & found a very tiny little burr on the belt but figured that shouldn't cause the problem.
Not wanting to waste any more time with it & chance thet burr as the problem, I explored my options. He had a 6.5mm STW reamer & this 6.5mm - 300 Win Mag reamer. Wanting to seat my bullet out decent & with a goal of 3250 FPS with a 140gr, I figured a 6.5mm - 300 Win Mag would do the trick.
Just guessing at where to start, I tried 79gr H870. This gave me 3274 FPS. The 1 trip I have made it to the range since completion I shot this group. Keep in mind it was -31 that day, so I am super pumped about what it should do when I can get to the range & concentrate. This group was hurried for obvious reasons
The last 3 shots were the lower left ones.
From the short time I have had this rifle it looks to me you can edge the 26" 264 Win Mags performance by around 50-60 FPS in a barrel that is 2" shorter.
It does have a wicked muzzle flash though