Copies of the Webley BULL DOG were made in Belgium and USA. The real webleys have "THE BRITISH BULL DOG" stamped in 2 lines on the top strap, with one line stamped on either side of the sighting groove. "BULL DOG" is two separate words on a real webley, and all capital (upper case) letters. Some Belgian and US copies used hyphenated "BULL-DOG" and one word "BULLDOG" stamped on the topstrap.
On the earlier webleys the stamping read from cylinder to muxzzle, and some of the later bulldogs had the stamping read from muzzle to cylinder.
The Webley Bull dog (aka "Webley No. 2") was produced from approx 1879 - 1914, with just over 100,000 known to be made. I don't have a reference for date of manufacture by serial number, however you could find out fairly quickly on the antique status by calling the CFP and asking them. They will look it up on the FRT and should be able to tell you the cutoff for the antique ser no.