All guns seem to take a value hit when used, but it isn't a progressive hit like with cars.
IE, a new car is worth X amount of dollars, a 5 year old one is worth some fraction of that, and a 10 year old one is worth a much smaller fraction.
Typically, a new gun is worthy Y amount of dollars, and a used one of any age is worth a fairly high fraction of that (that decreases only due to condition issues).
Now for guns that are out of production and have no new price to compare against the math is harder since inflation has driven up the used price, but overall as stated, much don't seem to acrue value so much as they tend to just hold it well.
That's one of the reasons I like to buy used guns when possible. The hit vs the new price has already been taken and it typically won't deprecate any further.