I have used this type of metal receivers in the past projects.
Brand:Hurricane M733
Manufacture type: Die cast aluminum
Insignia / logo / selector finish:all markings engraved
Finishes available: Gray
Insignias available: Colt
Included with body: Receiver pins, ejection port cover, forward assist knob and one piece metal hop up
Working furniture?: Same as TM M4 series if the parts are complete
Metal hop up included?: Yes
Fitment with gearbox: Almost all aftermarket gearboxes fits fine. Perfect for Prowin gearbox with minimal modifications.
Fitment with other parts on assembly: None
Magazine fitment: A bit tight if not using a TM M4 Mag. Minor filing required for other mags to fit.
Notes on assembly/issues with metal body: Everything fits like a glove.
Overall rating: 8/10.
Brand:Guarder SR15 Gen 1
Manufacture type: Die cast aluminum
Insignia / logo / selector finish:all markings laser etched
Finishes available: Flat Black
Insignias available: Knights
Included with body: Receiver pins, dust cover, ejection port cover, forward assist knob and plastic one piece hop up.
Working furniture?: Same as TM M4 series if the parts are complete
Metal hop up included?: No. Hop up is made of plastic
Fitment with gearbox: Almost all aftermarket gearboxes fits fine.
Fitment with other parts on assembly: Lower receiver need to be modified so that upper and lower will close properly.
Magazine fitment: A bit tight if not using a TM M4 Mag. Minor filing required for other mags to fit.
Notes on assembly/issues with metal body: Everything fits like a glove if the modified right.
Overall rating: 8/10.
Brand:Guarder SR16 Gen 2
Manufacture type: Die cast aluminum
Insignia / logo / selector finish:all laser etched
Finishes available: Flat Black
Insignias available:Knoght Stoner Rifle
Included with body: Receiver pins, ejection port cover, forward assist knob and one piece plastic hop up
Working furniture?: Same as TM M4 series if the parts are complete
Metal hop up included?: No
Fitment with gearbox: Almost all aftermarket gearboxes fits fine.
Fitment with other parts on assembly: None
Magazine fitment: A bit tight if not using a TM M4 Mag. Minor filing required for other mags to fit.
Notes on assembly/issues with metal body: Everything fits like a glove.
Overall rating: 9/10.
Brand:King Arms Troy and NOVASKE
Manufacture type: Die cast aluminum
Insignia / logo / selector finish:all markings laser etched
Finishes available: Matte Black
Insignias available: Lots to choose from
Included with body: Receiver pins, dust cover, ejection port cover, forward assist knob, bolt release, gearbox pin, and one piece metal hop up.
Working furniture?: Same as TM M4 series if the parts are complete bolt release is funtional.
Metal hop up included?: Yes
Fitment with gearbox: Almost all aftermarket gearboxes fits fine.
Fitment with other parts on assembly:None
Magazine fitment: Mag wel is a bit tight for the mags. Minor filing required for other mags to fit.
Notes on assembly/issues with metal body: Everything fits like a glove.
Overall rating: 9.5/10.