Getting armour with +8 or +9 defense is expensive, so there shouldn't be too many opponents with defense in the mid to high 20s at most. So even with a low BAB, if you roll 15 or above, you should still hit, just not as often.
ALTERNATIVELY.. instead of shooting AT such a well armoured target, use area attacks. Autofire spamming, grenades, use other attacks that incapacitate the target, and spam them like crazy. flash bangs, trip wires, nets, tear gas, and with higher tech you got gravity snares, sonic weapons that cause nausea and the like.
Even if the target has higher saves, having to save repeatedly will eventually fail some, and then get hit with penalties, and just piling on different types of penalties. Causing bleeding/wounding is a good way, get a couple of applications of bleeding, or anything that causes damage over multiple turns helps. Forces the target to either suffer continuing damage, or stop and heal, and if they stop to heal, distracted, easier to hit.