let a machinist in on this one
there too many alloys of steel, stainless steel and aluminum to name
6061 aluminum is a favorite, also are the 2000 and 7000 series aluminum alloys, im pretty shure good ol' Eugene Stoner came up with an AR-10 model that had an all aluminum barrel. im pretty shure the 2000 series arent used in firearms because they were especially prone to stress cracking and corrosion. 7075-T6 like prelaw09 said...
440 stainless steel and others in its grade (440A, B) are very common in most knife blades. i gest-i-mate there is about 140 types of stainless steel.
300 series is also popular. 316 stainless is what you would call surgical steel.
as far as regular steel, buddy, i dont know, i couldnt even guess how many kinda there are. stuff like low carbon steel is what i used a lot for machining on, because its fairly cheap and also soft, high carbon steel on the other hand is very hard. (a simple rule of thumb)
once again, i cant really say what kind of steel (its exact alloy #) is used in gun parts.
speaking of which, has anybody ever tested a gun barrel for its rockwell hardness? i really want to know now.
self influenced curiosity at its finest
and yeah, they a lot of older guns are made with brass. like the brass framed 1858 remington navy cap n' ball revolver that hides under my bed...
i also seen a few derringers (blackpowder) that had solid brass barrels. .32 caliber i think...
sorry, but im not that good into wood. cocobolo is a fine exotic wood used in some grips. most synthstic gun stocks are simply glass filled zythel of something like that.