Hello JBRS92,
Welcome to the Forum.
Assuming your modifications are intended to operate as a standard Modelgun. my first thoughts would be to try Tanaka Evolution cartridges and MG 5mm caps.
Do you have any standard cartridges with your model ?
If the steel parts you've fitted are for Live fire or Blank firing use I wouldn't recommend attempting to fire any ammunition with it. Modelguns are just that, Models. They aren't anywhere near strong enough to handle the enormous pressures generated by Live and Blank ammunition.
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Cerwyn
Hobby collector of Replica model guns and Militaria.
also member of Living History Reenactment Groups.