Antique what?? I would not use it or any chemical remover on an antique gun of value.
For tools, rusty parts, guns parts with no historic value, absolutely. Evaporust is the best thing I have found. It does not bother the base metal at all, do etching or alterations to the original finish texture. When I can I use it in a heated ultrasonic cleaner.
For blued gun parts that have rust and a finish remains, boil them in water. The rust will become much softer and will be easily removed with steel wool of a carding brush. It may take a couple of passes. You are converting the rust to rust blue. I recently did a rusty crusty 100 year old pistol that way. I boiled all of the parts on the stove top for a while then cleaned as normal. I looked really nice after.