Mister Boney Pants Guy just dropped me a 81% sham.

[Atom1c]

I was just farming a chaotic evil monk for my gunzerker when i suddenly killed MBPG and he dropped me a sham in UVHM. Can someone tell me how accurately rare this is?

[His Majesty's strawberry cart]

I have only got one or two with multiple characters and many hours, you may use the sanctuary locker for other characters for that drop

[Renfrew]

A world drop Legendary is always 1 in 10000 (i.e. 0.009%)[www.gearboxsoftware.com] assuming the game has not been modified in any way.

If you also want to know how rare that specific sham is, most shield parts are weighted equally, and while capacitors specifically are weighted differently, shams have restricted capacitors (no Maliwan or Torgue). This means there are only 100 unique variants of the sham. They would all be equally as rare if it wasn't for the fact that the Tediore capacitor is more common. There is a 40% chance for Tediore and 20% for each of the 3 other manufacturers.
That means to get a specific sham with a Tediore capacitor the chance is: 1.6% chance
For any other specific sham the chance is: 0.8% chance (this is also the odds for the 94% sham)