Not really - If you are good at repair and know what's what, you can repair your guns the right way.
Anyways - I would rather suggest something like this:
To repair a gun you need junk OR other gun. Depending on how much you would use on it, you have higher % of succes (but you cant reach 100% just using up a lot of junk/guns).
That way it makes sense - you need to repair a gun, you can use parts from the other one or make/find some from junk. The better at repair you are, he easier it is, but if you have a lot of shit to use up, its easier to find fitting part.
Something like this. Then again- i just wrote it without thinking much.