Why don't you have a look on the airbus industrie website. All such details are readily availible. I think there is some confusion here thought - i believe you may have confusion between the early airbus A300B2/B4 models and the latter current A300-600R. As already pointed out, the aircraft American uses is the A300-600R, which, without a doubt can easliy handel a transatlantic (to the northern most parts of america anyway) flight. According to the Airbus Industrie product briefing-A300-600R, issue number four, april 1997,
the A300-600R with CF6-80C2A5 powerplants rated at
61 500 lb thrust, has a range of 4000 nm, allowing 200nm reserves, with a payload of 266 pax & baggage.
For those of us who like to use the metric system, this equates into about 7200 km plus reserves. The GE
CF6-80-C2A5 powered A300-600R has full FAA and JAA 180 minute etops certification. In Europe, the JAA grant the PW4158 powered A300-600R 180 minuted Etops, and etops operations with the PW4158 engine have not yet been requested to the FAA. All A310-300 models have full 180 minuted etops certification.
By comparison, the A300B4-200, the longest range verson of the early A300 series has a range of 2900 nm, or 5350 km with a payload of 251 pax + baggage. (A3002/A300B4 product briefing, issue number 2 april 1993) shut down rates for the A300B2/B4 mean the requirements for 180 minutes etops, however i don't believe anyone has requested etops operations with A300B2/B4 aircraft. This would most likely be due to range. The early airbus widebody was designed to serve routes that were the domain of the 727, 737-200, and DC-9, not to mention earlier types again like the 720. So, its range and payload abilities compare favourably with these aircraft. It was not designed to be transatlantic, and when into service flying with Air france between London and Paris intially. Today, considering the purchase price of an A300B4, which is about the same as an early 757, the aircraft is quite good value for money. its operating costs, even with theh 3 person crew is substancially lower than a 737-300, and on trancontinental routes has quite a good job for a long time now. I wouldn't hold my breath waiting fo this aircraft to fly long haul though. Think of it like its a really big 737. The A300B2/B4 only had moderate success - why, well, i blame the french TGV trains. When you can travel at 300 kmh, on a short hop, nobody minds waiting a few hours for a cheaper price.
and rail will always cost lest to produce than air, so, demand crashed big time and killed the concept of short range widebodies.