The M14 differs from the M1 Garand mostly in its gas system, length of action and in what stops forward motion of the op-rod.
The Mini-14 superficially resembles the M14 in trigger group and receiver but has a gas system that doesn't resemble the M1 Carbine, M14, or M1 Garand. It probably resembles the M1 Carbine the most, but the big difference here is that the Carbine has a very short stroke piston and gas isn't intended to hit the op-rod. On the Mini-14, The op-rod acts as a gas cylinder or cup against which a gas spigot off the barrel operates.
Hope this helps.
- Ivan.