The 270 WSM brass I have bought varies in case capacity more than any other I have worked with. This was from relatively new lots of brass so it may be more uniform now. One batch was so thick I needed to neck turn them to avoid high pressure.

I have not used Retumbo but with both R25 & R26 & 140s I get right at 3200 fos. I would work up your Retumbo loads by velocity and stop when you hit 3,200 fps even if you are not at listed max. The cartridges with a SAAMI max of 65,000 psi don't allow much wiggle room at maximum. Doesn't take much to get a spike at the higher pressures.

"When you disarm the people, you commence to offend them and show that you distrust them either through cowardice or lack of confidence, and both of these opinions generate hatred." Niccolo Machiavelli