Inquisitor 1300

[Indy-trier]

I have a full grid and the extra/missing letters but am trying to understand the wordplay for 27D and 31D before I start struggling with that 7 word phrase. I have answers for both and they fit well with my across answers so I just need to understand them! Any help would be appreciated.

[rabet]

27D # ROT = collapse; SAT = bore (past tense of "bear"); N is the extra letter.

[Indy-trier]

Thanks Rabet. That makes perfect sense. I hadn't connected SAT with BORE at all.

[shikasta]

31d MUSI* (music cut, badly=anagrind) in O (11) M (minutes) = OSMIUM (heavy metal)

[Indy-trier]

Thanks Shikasta. I had the right answer but couldn't make sense of the 11 bit. Still not sure why that means O though.

[rabet]

O is the Roman medieval numeral for eleven.

[Indy-trier]

Thank you Rabet. That ties up all my loose ends!