Hate to throw this spanner in your works, that front handle should swing left/right so the gundam can hold it in his hands. The swinging mechanism isn't included on that old and outdated HG's rifle. also evidenced by the fact it's literally 1 part on the sprue rather than at least 2 as they are these days.
You can see it on the PG's rifle:
This may be obvious but its the cylinder on the rifle. But don't feel BAD the work you've done is stellar, just, if you're after detail, i hope it's a mildly quick fix. it looks like you're using fusion 360 so that's usually quite quick to get to do your thing. Recommend looking at pictures of the PG to get the detail you want
also just realised you've replaced it's targeting dish with some... um... super detailed holes!