Making a new weapon in HL is more difficult than it sounds.
1. HL models needs to be simple. Otherwise the engine can't handle them.
2. They need to fit exactly into the holders hands.
3. They must be coded properly. Think of a gun where the bullets come out 3 inches above the chassi.
4. It's time consuming to make a good model.
5. You need two models for each weapon. One for the world which will be seen from other players and one which the player will hold in 3D.
And there's more, but I don't want to spoil your gun-making.
Don't give up.