Unless you have a lot of hang over you have no problem. I have put a lot of weight on them. The knee screw and nut are what carries the load mostly. Be sure to lube the threads well. I tried to find the specs in my book but found none.
edit: Bridgeport web site spec says 750lb max. A 12"wx18"lx12"h block of steel will weight about 733lb so I don't think I have had over 500lb on any I have used.
That's 750 lb centered on the saddle. Less as you offset the table. I would limit table loads to 100 lb on the end with the table offset to the extreme.
Turret mills are weak in the saddle department. The saddle is short and narrow meaning the long table demanded by customers these days can be cantilevered out to alarming distances. The concentrated loads on the ends of the saddle wears hollows in the table and humps the saddle.
That's the beauty of the turret mill design with its two axis head tilt. You can get to every detail of any part you can fit on the table by swiveling the turret and extending the ram. So why is it I see turret mills with the ram straight ahead and the table offset to the max with a heavy awkward part on it?
The turret/ram design adds 20% to the cost of the mill. Why not use it?