[PyGame] Ammo is random, but it shouldn't

[Piethon]

Hello.
I have a little problem in my game, that I am coding with pygame.
I've tried adding ammo, to my shurikans, that you can't spam them.
I've set the SHURIKAN_AMMO to 20, and I can shoot 2 times. When it is at 500, I can shoot like 56 times.

Here's the code (parts of it):

class Player(pg.sprite.Sprite):
    def __init__(self, game, x, y):
        self.weapon = 'shurikan'
        self.shoot_ammo = True
        self.SHURIKAN_AMMO = 500

    def get_keys(self):
                if keys[pg.K_SPACE]:
                    if self.weapon == 'shurikan' and self.shoot_ammo == True:
                        self.SHURIKAN_AMMO -= 1
                        if self.SHURIKAN_AMMO < 0:
                            self.SHURIKAN_AMMO = 0
                        if self.SHURIKAN_AMMO == 0:
                            self.shoot_ammo = False
                        if self.SHURIKAN_AMMO > 0:
                            self.shoot()

        def shoot(self):
        if self.shoot_ammo == True:
            now = pg.time.get_ticks()
            if now - self.last_shot > WEAPONS[self.weapon]['rate']:
                self.last_shot = now
                dir = vec(1, 0).rotate(-self.rot)
                pos = self.pos + BARREL_OFFSET.rotate(-self.rot)
                self.vel = vec(-WEAPONS[self.weapon]['rate'], 0).rotate(-self.rot)
                for i in range(WEAPONS[self.weapon]['count']):
                    spread = uniform(-WEAPONS[self.weapon]['spread'], WEAPONS[self.weapon]['spread'])
                    Blowpipe(self.game, pos, dir.rotate(spread))

I have made a list, for the different weapons, where rate, spread and other things are in. This is the one, for the shurikan:

WEAPONS['shurikan'] = {'img': 'shurikan.png',
                       'speed': 575,
                       'lifetime': 800,
                       'rate': 400,
                       'kickback': 0,
                       'spread': 2,
                       'damage': 12,
                       'size': 'shurikan',
                       'count': 1}

I really don't know, why this is happening. If you have an idea, then please tell me. Thanks so much.

Piethon.