I have a 28" or (27.5) Barty heavy palma screwed in to a 591, t4a with heavy fill. A bugholes brake on the end at about 2". My total length to breach is 28 and 3/8.
Again subjective as stated above and definitely not scientific at all, but I did a half ass balance check way back when without the scope mounted and it wanted to sit in my palm directly under the front action screw. Originally I was not planning on running a brake till I had my smith run a 6x47l reamer thru the original dasher norma chamber, so I probably would have went down to around 26" finished on the bbl length.