8208 XBR would be a good alternative but I'd try using a drop tube and getting a bit more powder in that case.
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I ran it in QL and you should be over 2400fps with 43 grains unless you're using really roomy brass.
As for 2800fps, not with a 175.
What's your shooting position?
Is it a degradation of your position causing the groups to open up?
Bedding could very well be your issue as well.
Way to many unknowns to call it a barrel issue right off the bat.
I'd start at 50 grains of Hybrid 100V with a 140.
Then again I have a Quickload and several manuals to reference.
I would highly recommend buying Quickload as it give you a scientific approach with predicted chamber PSI's instead of the anecdotal and often inaccurate data found in reloading manuals.
I'd use 6.5 Rem mag data up to the point you have pressure.
With your more generous magazine box your loads with 140's will be able to outperform the 6.5 RM by a fair margin.
Your case capacity is almost identical (72 grains) the the 6.5SAUM/4S that the forum is buzzing about.
You should be able...
FWIW, I have the x32 on my 16" AR and have taken it out to 1000 without the optic being a weak link.
Using an ADM 20 moa Recon mount I ran out of adjustment and had to hold an additional 1.5 mils.
Around here 600 would take one turn plus 1/2 mil.
With another 2" of barrel, different load and a...
Temp stability is not going to be an issue with 4064.
I prefer it to Varget in 308. YMMV
IMR 4895 is pretty great with 155's as well.
I had good accuracy and 3000FPS from a 26" barrel.
175's(178) and 4064 out of my 20" were a knot cutting combination
Any chance you're shooting a REm 700 LTR?
These two were high on something.
Interesting firearms handling and use of sling.
http://embed.contagiousmedia.com/embed/sub/watch-the-entire-video-here-n96wxp-vt9p?uri=watch-the-entire-video-here-n96wxp-vt9p&cb=1406167310...