It is indeed a cargo type chute....your crate is actually for 20mm MG FF ammo...the MG FF was an aircraft mounted gun, used in ME-109's, FW-190's, etc. They are Minen-Geschoss, or mine shells, special thin walled shells with extra HE useful for blowing wings off of bombers and such.
Nice pieces, I doubt if they belong to each other though. The crate was probably just a useful container for the chute