Bow Alternatives are for your personal selection of weapons to use for your purposes.
To use these as your bow/rifle, follow these simple steps.

1. Decide what you want to use.
2. Copy the weapon and create 4 of the same texture. Edit them as needed for animations.
(name the textures as follows) bow_standby bow_pulling_0 bow_pulling_1 bow_pulling_2
(if you use one of the pre animated options, skip step 2.
3. Follow this path. assets/minecraft/textures/items
4. place the four files in the items folder. You should see a message asking if you 
want to replace four files.
5. Enter the game and refresh the resource pack. You are done!

If something is wrong, reflect on the above steps to the letter.

Have fun!