Recoil Down and Recovery Speed can be increase to 2 making it easier of less recoil and faster recovery from damage taken(with Immunizer). Clust S All up is useful when its ammo explodes on contact.
Combination Rate-5% can be removed by 2 jewels that increase combination.
You can gem up to Recoil Down+3 with two FlinchFree Jewels (recoil+4, Reload Spd-2) and two Absorber Jewels (Recoil+1 Reload Spd-1) giving you an extra 10 points for Recoil Down while also giving you only 6 negative Reload Speed points. Leaving no space for Combo Rate Jewels you should gem your guns so you can remove Combo Rate -5%. This leaves you to decide what charm to use as it would not affect the armor set in any way.