I'm not sure how you would get bullets to come out of it but the only way I know how to iz by using the actual Gecko Codes.
For instance, using this code>4A000000 8098D528
D2000000 00000003
2C0600XX 40820008
38C000YY 60000000
90DD08C0 00000000
<You can change XX and YY to replace things. XX=Item to be replaced. YY=Item to replace old item.
And the things you can replace XX and YY with are:00 Assist Trophy
01 Franklin Badge
02 Banana Peel
03 Barrel
04 Beam Sword
05 Bill (?)
06 Bob-Omb
07 Crate
08 Bumper
09 Capsule
0A Rolling Crate
0B CD
0C Sticky Bomb
0D Cracker Launcher
0E Cracker Launcher Shot
0F Coin
10 Superspicy Curry
11 Superspice Curry Shot
12 Deku Nut
13 Mr. Saturn
14 Dragoon Parts
15 Dragoon Set
16 Dragoon Sight
17 Trophy
18 Fire Flower
19 Fire Flower Shot
1A Freezie
1B Golden Hammer
1C Green Shell
1D Hammer
1E Hammer Head
1F Fan
20 Heart Container
21 Homerun Bat
22 Party Ball
23 Manaphy Heart
24 Maxim Tomato
25 Poison Mushroom
26 Super Mushroom
27 Metal Box
28 Hot Head
29 Pitfall
2A Pokeball
2B Explosive Box
2C Ray Gun
2D Ray Gun Shot
2E Lipstick
2F Lipstick Flower
30 Lipstick Shot (Dust/Powder)
31 Sandbag
32 Screw Attack
33 Sticker
34 Motion-Sensor Bomb
35 Timer
36 Smart Bomb
37 Smash Ball
38 Smoke Screen
39 Spring
3A Star Rod
3B Star Rod Shot
3C Soccer Ball
3D Superscope
3E Superscope shot
3F Star
40 Food
41 Team Healer
42 Lightning
43 Unira
44 Bunny Hood
45 Warpstar
So If you were to make XX=2D, then YY=something that resembles a bullet in your mind out of that list(lol), then you would just need to add the new code to your .txt file and then add it to your .gct file on your SD Card and BAM! you got a Ray Gun that shoots some random crap! 
On a side note: Not all codes that you make for Item Switcher will work, I have tried some that didn't work for me. It might have just been me but idk so yea. Hope that helps you.