I realize this is not an ideal powder but desperate times call for desperate measures. I have been able to acquire 8 pounds of winchester 760 powder. Has anyone tried this powder with this cartridge? I'd like to use it with a 107 sierra for a CPT load.

Pretty slow, but I've never tried it, so I don't know.
The slowest powders I've had decent luck with are MR2000 and Big Game.

Do you have access to Gordon's Reloading Tool or Quickload? They would at least give you an idea.

If I remember this eve, I'll run some scenarios on either Quickload or Gordon's.

What is your barrel length?

I have not used Winchester 760 on a 6.5mm BR, although I have used VV N550 in a similar caliber 6.5mm Viking with heavy bullets 139/144 Lapua. Winchester 760 is temperature sensitive but if you do not have any other powder go ahead and use it. Start with 30 gr and go up .5 gr at a time. I remember I used as much as 34 gr. of VV N550 on my ram loads. The brass made by Norma and Lapua is very strong compared with the 7mm BR made by Remington. If your bolt is like a Rem 700 and is not bushed proceed with caution when using heavy loads so you will not blank the primers. I recommend you use the CCI 450 SR magnum primers. Since you are planning on only shooting c,p and t with it there is no reason to go higher than maybe 32gr.

Back in the 90's before the VLD bullets and before the 6.5 became popular I got a hold of a rifle with 3 barrels chambered in 6.5mm Brian which was a 308 case formed with a long neck to reduce the capacity of the cartridge and it performed like something in between a 6.5mm BR and a 6.5X47 Lapua. The only bullets I could buy at that time were the 120, 140 Sierra and the 144gr Lapua bullets. I was using Winchester 760 on my loads and at a State Championship where we were shooting 60 round matches instead of 40 I found out that Winchester 760 was not the ideal powder to use in hot weather because after the first 10 rounds the barrel on my rifle got very hot and the last 5 rounds enlarged the pocket primers on my brass to the point that they could not be use again. If I remember correctly I was using something like 34gr of Winchester 760.

Loneringer's advice is good.
Quickload shows the following with a 24" barrel and 107 Sierra. W760.
30 grains, ~2,300 fps @ ~32,000psi
31 grains, ~2,400 fps @ ~36,000psi, 84% burn
32 grains, ~2,500 fps @ ~40,000 psi
33 grains, ~2,600 fps @ ~44,000 psi, 88% burn
34 grains, ~2,700 fps @ ~48,000 psi
I did and wrote these down quickly and I make mistakes, but they are similar to Loneringer's advice. I think if you chronograph your loads and they show a velocity progression similar to Quickload, about 50 fps per 0.5 grains (one half grain), and the velocity is similar---given all the factors other than loads that can cause velocity differences, you should be on the right track to getting it to work.

What velocity do you generally get with 107's?

I have been running about 2300 with 107s in my tcu. Those loads will do great if the reality matches theoretical. Thank you so much for the help.

Don "Dakota" Clayton