how can it be
 

How can a prop be more than 100% efficient? I have a new prop an on the invoice it states that target speed 190mph@2800rpm. Is my math wrong? (rpm X pitch X 60) / (5280 X12) = 185.6 What am I doing wrong? Someone please explain in layman terms.
Thanks G.P.

yes
 

they were in a dive when testing. :D

Pitch is imprecise.
 

Efficiency has absolutely nothing to due with some propeller geometric angle at some radius. Effiency is propeller-thrust,lb, times forward velocity,fps, divided by the engine power times 550. A propeller with a stated "pitch" of some value will have different speed-rpm characteristics depending on the airframe drag. Obviously, the more drag an airframe has, the more work will be required to pull it through the air. With a FP prop, that will translate into higher prop AOA and lower rpm. It's the same as a wing; load it down more and it will have to operate at a higher AOA. There is only one true "pitch" value, and that is TAS, mph, times 1056 divided by rpm, which gives the "effective pitch". In your case, they say that the prop has 190 times 1056 divided by 2800 = 71.7" effective pitch. That will only be true on one airframe-drag - engine-power condition.