I had my LBS order a CB cyan BB to go on my 303 crankset, but its apparently not compatible, something to to with the interface of the crank arm and BB shell. Anyone know if the Zipp 185 BB is the only one compatible with this crank?

https://www.zipp.com/Products/Cranks/...%2cProductName
The combination of the two components with Zipp's proprietary 6AI/4V hardware result in a Crank/BB system that is more than 100 grams lighter than competing crank/BB systems.

they use the word "proprietary". ask zipp.

Gah, "proprietary." I hate that word. Back when I was doing biophysical research, we wanted to know how much hydrogen peroxide was in a hydrogen peroxide buffer we were considering for an experiment. Called the company..."Sorry, sir, but the formulation is completely proprietary, and we can't tell you what is in it."

That's not what I call science.

So we made our own buffer.

Back to cycling, I'd sacrifice a weight edge for compatibility, flexibility, and durability. But I'm not in the business of racing or even trying to go all that fast.

Best of luck. I'd wager you'll be stuck with the Zipp BB.

To my knowledge, Zipp 300 cranks use an ISIS BB with 108mm spindle.

As the ISIS interface is standardized, any ISIS BB with a 108 mm spindle length will work with our 300 crank, presuming you have the appropriate BB for either an English or Italian BB shell. I'm a bit confused as to the nature of the problem as you mention the interface with the BB shell when I suspect you mean the spindle itself; can you elaborate on the problem?

sounds like his lbs told him that?