Found out that the MX 6.5mm cannot damage the HEMMT engine block when it is unsuppressed. Fired around 600 rounds into the engine block but was still operational. If you put a suppressor on the MX it is able to disable the HEMMT as normal (~11 rounds).

MXC with or without a suppressor also cannot damage engine block.

Promet variants & MXM, MX SW can damage engine block whilst suppressed & unsuppressed