I'd recommend you take a look at the wowhead guide - there's an entire section on the execute range rotation there.
People spamming MS in execute range (assuming Slayer raid build) are doing it wrong. Don't follow them or give their opinion any weight.
2x execute BS>MS and weave in OP and slam
You should never press slam in execute range. Generally your prio is (off memory, I'm on mobile rn so can't check exactly; again refer to the wowhead guide for a source of truth)
- opportunist OP if not already at 2x martial prowess
- 2xEP MS
- execute
- OP without opportunist
In practice, this usually means pressing MS every 4th gcd with 2 exes in between, and either a 3rd exe or an OP as well. The order of those doesn't matter much, obviously accounting for opportunist procs. You could potentially end up doing MS on a 5th global if you get multiple opportunist procs as well.
A decent baseline "close enough" is MS > exe > exe > OP > MS as a default.
For BS, you only want to use it during CS and when you have 2xEP since unhinged MS will use your EP stacks