I would use opposed rolls from page 34: use player's combat percentile, and have the opponents roll against it or be suppressed, lose action points. Expend ammo also, has to be a semi- or automatic weapon.
If Robin D Laws isn't doing anything more with the Gaean Reach by Jack Vance, that would be an interesting sci-fi IP to make BRP.
https://en.wikipedia.org/wiki/Gaean_Reach