I'm working on a 150 gr load for my daughter's 7mm-08. It's a Vanguard with a 20" barrel. It shoots the Sierra 120 gr Prohunters extremely well.

I tried both the Sierra 150 gr and the Swift Scirocco; no dice.

I'm seating at 2.780", the same was the 120 gr. The lands are at 2.795".

Should I try a shorter or longer seating depth?

Book calls for 2.80 oal
Is it a custom chamber?

Book calls for 2.800" which is the factory seating depth with Remington SPCL bullets crimped. The Rem bullets have a shallower ogive than Sierra which need to be seated deeper in standard cut chambers. I have to seat Sierra 150gr GK bullets to 2.740" and 140gr GK to 2.780"in my Marlin XL 7mm08 which is the same COAL I use in my son's Remington SPS 7mm08.

If I seat at the same COAL as for Rem bullets the Sierra 140gr and 150gr GKs will jam in the rifling of the Rem SPS enough to pull out of the case when extracting an unfired cartridge.