Its not profoundly rusted but theres a small layer in the bores and barrel. The outside doesn’t really have any rust on it. Would that evapor rust stuff wear out the inner of the barrel or cylinder bores making them slightly wider? I dont want to do any damage to it
No.
The Evaporust cannot harm the metal no matter how long that it's left in the solution.
It's not an acid.
It's water based and is also harmless to skin.
All it does is dissolve rust by separating the rust from the steel.
Because bluing is actually rust it will remove that too if left in contact with it.
But there will probably be some small pits where the rust attacked the metal which is inevitable once the rust is removed.
How much pitting would depend on the severity of the rust.
Very light rust may not leave any pitting, or barely noticeable.
You're the only one that knows how much rust there is.
But the amount of pitting depends on how deep the rust is.
Removing the original bluing from an original antique revolver can reduce its value.
But then so will the rust.
A curator would need to come up with a method for removing the rust while doing the least amount of harm to the rest of the gun.
I'll admit that it would be difficult to effectively seal the bore and chambers to allow the Evaporust to work without coming into contact with the bluing.
But since we don't know how hard it would be to remove all of the rust, then the bore might keep deteriorating.
There may also be other products worth investigating too.
It depends on factors that I don't know about and can't predict, such as how other methods will affect the metal and how deep the rust is.