I am familiar with the HobbyFix M4A1, M16A4 and XM177E2 models. They are the most realistic M16/AR-15 models available. They use real magazines and can cycle real dummy carts. But they are dummy only models so they cannot use plug fire caps. Real parts like stocks, grips and handguards fit as far as I know.
Sadly these models are very rare and very expensive. The M4A1 and M16A4 were last produced in 200/2001, the XM 177E2 in 1993.
Even in Japan such a model is regularly sold beyond the 200.00o JPY price tag, even if it is a used second hand item.