Sig Pro/ Sig Pro B??

Can anyone tell me what the difference is between the Sig Pro and the Sig Pro B. The price difference is $150. Any help would be appreciated.

"My faith, my country and my family will guide me; nothing more, nothing less" -Gen. Tommy Franks

Jess Hoffman
Mooseyard Precision
LE Supply & Firearms
NRA Certified Instructor
Shawano, WI 54166