First, you must have Bouncing Betties and enough for any perk and also enough for a gun.

Place 1 Betty anywhere. Then, go to a Perk machine and take out a Betty. Place it in front of the perk and right when its placed, buy the perk. It may not work, but you must time it right.

If done correctly, you should be holding no visible weapon. Remember you must have only 1 Betty.

Now you have no weapon. Buy a weapon off the wall or random (I buy a Kar98k or Springfield because its cheap).

You can always trade weapons. You can get all the guns in the game, but you must be down yourself to lose all your perks.

You won't lose your guns, but you can buy your Perks again so you can have more weapons.

Remember this only works for Zombie Verruckt.