i get a chuckle out of how some people throw around "aircraft grade" as if its some huge deal. aircraft grade doesn't mean a metal has been though a V.A.R process and with todays use of the word it doesn't mean much besides the fact that alloy is used on an aircraft.
some engine parts and other critical parts will be made out of steel which has been though a V.A.R process however a lot of other parts made from the same material wont.
so by that standard any machine shop has tons of "aircraft grade" material, 4140, 4130, 4330, 4340. i mean if rick really wanted to he could market his action as 15-5PH aircraft grade because 15-5ph is a very common alloy on aircrafts and there is no actual specification on "aircraft grade"
as for 4340 vs 15-5ph ( both being either V.A.R or E.S.R) 15-5 is typically more expensive and harder to work with.