If you didn't know already, the patch last weekish had some balancing effects (natascha anyone?) as well as a pretty big nerf to the overall number of criticals flying around.  For those of you who prefer cliffnotes, here I go:

Crits % is made up of a base percentage, and then a modifier that increases that base percentage when you do alot of damage in a short period of time.  (the idea being that skilled players or offensive players are rewarded for going out there and doing the business of killing)

That said, here are the changes for ranged weapons:

Prepatch Base chance= 5%      

Patched base chance= 2%

------------------------------------------------

Prepatch Max chance with damage modifier = 20% (1600 damg required for max)

Patched Max chance with Damage modifier = 10%   (850 damg required for max)

It has basically lowered the overall chances for us to get a crit....but puts more weight on your skill level now because its much easier to attain the max modifier (ie 1600 vs 850).  Thus skilled players are going to crit alot more than non-skilled, but overall they are going to crit less than they did before the patch.

You can also go here to get a more in-depth break down, with graphs and such...curtesy of Valve