In edit mode, tap A twice to select all the vertecies, then tap CTRL+N to flip all the normals outside. Should fix a handful of issues you're having. Secondly, tap ALT+J while you still have all the vertecies selected, this will force all of them, at least the nearest groups, to be Quads, which are easier to model with than triangles. Your topology is looking really highpoly and in other areas, very low poly. Use a decimate modifier on parts of it to fix that. Likewise, delete those loops of vertecies that are making seams in the model, on the stock and the trigger guard(?), and join the two objects, select the end loops of vertecies (Alt+ Right click) and connect them by tapping F -> skin edge loops.