Interesting ideas, but ultimately the changes pretty much removed everything that made me enjoy the weapon in the first place.
Hitscan + reduced accuracy means long range fire becomes less about skill and more just "point directly at target and hope for good RNG" which I find distinctly unsatisfying both when using the weapon and when being shot at by it.
Semi-auto mode's limited fire rate means if you're trying to click at a rate about equal to the weapon's fire rate, there's a good chance you click slightly too early and the weapon just doesn't fire, so you lose a full cycle.
Transition between semi-auto fire and full-auto feels clunky and unresponsive, it almost turns into a different weapon after holding down the trigger for a while which is just... weird? Being able to swap into super rapid fire mode but also not being able to do it immediately when you want it just doesn't feel good at all to me. I did see you added an indicator showing the swapover between semi-auto and full-auto fire, which is definitely nice to have but doesn't really make it feel any less awkward to use.
Honestly, I don't think rivet needs full-auto capability at all and I'd look toward balancing it around being a pure semi-auto weapon instead, with maybe with greater accuracy and a bit less velocity than the previous version.
I do like the Garand ping on mag empty though.