There are many deviations of the methods I will give, but they all follow the same concept of how they are done. Camo essentially consists of layers of colors in different patterns. in this case, each layer is applied using masks or stencils to create patterns.
It is also important to make sure paint doesn't get anywhere that could damage the gun. Use painters tape or masking tape to cover these parts if they cannot be removed. You should tape orange tips, joints, and holes that lead to the inside of the gun.
Step 1: Stencils
Step 2: Makeing Stencils
To make digital stencils, use graph paper. Color in random sections of the "pixels" created by the graphlines and cut them out.
To make splotch stencils, draw blobs on some paper and cut them out.
Step 3: Tiger Stripe: Application
Digital and splotch stencils need to be attached with either adhesive spray applied to just thae stencil or tape loops. Spray is more exact but tape will adhere better to the gun and is less likely to leave residue.
So: spray your base coat, allow to dry. Apply stencils, Spray next coat, let dry, Apply stencils ect. ect. until you have sprayed all the colors that you want. After all the paint has dried on the last coat, remove the stencils and do the other side.
Step 4: Masks
The term mask refers to something that covers part of the surface to block it from paint. it differs from a stencil in that it is removed after only the area immediately surrounding it is sprayed.
Use local foliage as masks. Spray layers of colors with masks randomly all over the surface until you are satisfied. you can let each spray dry if you want it really smooth, but you don't have to. This will be much faster than a stencil job.
The G36c in the title was done with this method. it required only three coats, two sticks and three leaves.
Once again, you do not give it complete coats, except for the base coat. you are only painting the area immediately surrounding whichever stencil you are using.
Step 5: Sponging
First, apply a base and a secondary color, then spray some other colors into a pan so that the paint accumulates as a liquid, and apply it to the gun via a sponge.
A really nice tutorial can be found here ( his guns turned out much better to).