The Kap 40 won't be much of a problem. It's pretty good right out of the box. It's only issue is that it fires so quickly that you can easily expend the full 15 bullet clip in a split second. So for it I'd suggest learning how to burst it for ammo conservation.
For the B23R, my best advice is to set your shots up with the intention of bursting 2 to 3 times per kill. Sometimes you'll drop someone in one burst. Most of the time it takes two. For me the best attachment early on is extended mags. After that I really liked them dual wielded but you do lose some accuracy with them when you do that.