Well, if they can make plastic Sentinels they can make plastic guns. But also, remember, there was a good stretch in the 90s where Cable didn’t even use guns. He used the psimitar instead. Still, his being half techno-organic makes him vulnerable with or without guns. Like Wolverine. Or Colossus.
Bishop, on the other hand, can drop his guns and just get charged up from the electromagnetic energy that Mags throws off. And then theoretically could just stroll up to him and beat his old ass with his fists. Bishop’s a big dude who knows how to brawl.