What you're after is the WWII AIC (Ammunition Identification Code), which worked from the ORD-11 Standard Nomenclature List categories and was replaced by the DODAC (Department of Defense Ammunition Code), by the 1960s.
I'll use the one upthread as an example: S1ICA Bomb, GP, 500lb AN-M64A1 (Tritonal Filling), with transit hoops
"Bombs, Grenades and Pyrotechnics" were listed under SNL Group S, which gives the first character in the code.
Subsection 1 deals with "Bombs, aircraft, all types", so the second character is a 1.
The last three characters specify the type of ordnance and the packaging methods etc., however I don't have the relevant manuals which decrypt the whole thing.
These should be Ordnance Field Service Bulletin No.3-14 (Tentative) Ammunition Identification Code (A.I.C.) from 1942, and the expanded Service Bulletin 9-AMM 5 which apparently covers them all.
Some other examples from S1:
S1FKA 2 Bombs, Fragmentation, 23lb M72, with fuzes, in wooden crate
S1HTA Bomb, GP, 500lb AN-M64A1 (TNT Filling), with transit hoops
S1HWA Bomb, GP, 500lb AN-M64A1 (Composition B Filling), with transit hoops
S1GDA Bomb, Chemical, 500lb AN-M78 (AC Filling), with transit hoops
From S2, Fuzes and miscellaneous explosive components for aircraft bombs:
S2NLA 48 Fuzes, Nose, Bomb, AN-M126A1, in metal tubes, in wooden crate
S2NRA 25 Fuzes, Bomb, Nose, AN-M103A1, in metal tubes, in wooden crate
S2QNA 25 Fuzes, Bomb, Tail, AN-M100A1, in metal tubes, in wooden crate
S2QQB 9 Fuzes, Bomb, Tail, AN-M102A2 (.025 Sec Delay), in metal tubes, in wooden crate
S-3: Fin assemblies, and miscellaneous inert components for aircraft bombs:
S3FHB 20 Containers, 100 Arming Wire Assemblies, in wooden crate
S3JWA Fin Assembly, 250lb size, AN-M106A1 with/without accessories, in metal crate
S3POB 5 Arming Wire Assemblies for Bomb, Chemical, 100lb M47A2, in round metal tin
S-5 Pyrotechnics, military, all types:
S5PDC 72 Signals, Aircraft, Double Star, Red-Red, AN-M37A1, in wooden crate
I have the following AIC noted regarding your AN-M57 query:
S1DDA Bomb, GP, 250lb AN-M57A1 (Tritonal Filling), with transit hoops
Hope that helps,
PB