How do I give my companion his weapon back on Fallout New Vegas?

I am so mad, as in the confused mad, because when I went into the Tops casino, did what I needed to with Benny's gang. When I left, I was given my weapons back and Boone's rifle. When I try to give it back it isn't even in my inventory. But when I check my Pip-Boy, it's there and I can uses it. How do I give it back so Boone can help me again?