All I could find was this, about the 3913TSW, the last version of it with rail. Not sure if specs are exactly the same as standard 3913 and I couldn't find specs on the older version 3913TSW, prerail, short grip.
http://www.rohrbaughforum.com/sw3913tswreview.pdf
I actually plan on checking out the Shield in person and bringing my 3913TSW (prerail, short grip) to compare. Probably won't be able to take pics, unless the gunshop lets me.