I got myself an Brocock Contour .22 in Single Shot. There is an option to buy a 6 shot magazine, but it's quiet expensive. So I started thinking that there must be a way of making a magazine. I remembered people modifying cap guns to take 6 mm Airsoft BB's. I thought that this could work. As .22 pellets are 5.5 mm which is 0.5 mm smaller than an Airsoft BB. I got myself one and what do you know, they slide in perfectly. All cap guns are 8 shot so this gives me an extra 2 shots from the 6 shot magazine.

Step 1: Get a Cap Gun

First I would design your magazine, I used Google SketchUp to get an accurate image of the cylinder. And Sketchbook for tablets on Android (Layers are a big help) but GIMP can also do this.
You can get a cap gun for around £5 (I'd advise you to get a plastic cap gun. It's easier to work with in the next step)
Once it arrives you can check if your Pellets will fit in.
As you can see you can get approximately three stacks of pellets (remember sawing takes of a mm)
So once you have confirmed. that it will work you can move on to the next step.

Step 2: Cut and Carve Out the Cylinder and Make the Basic Casing

This step is very important.
When you finished sawing to the desired depth, you will have to file down the rounded part sticking out of the cylinder so that the Pellet can fall out.
I used the end of a BIC pen to fit snugly in the centre hole of my cylinder (now a cog).

Now Let's move on to the next step.
I used 3 mm plywood (because it's cheap and I had a decent size piece laying around) and super glue, the super glue will be used to laminate the pieces together.
Using the cog as a template to draw the space that will be occupied by the pellets. Draw around the cog and then attach the sides

Step 3: Fill in the Gaps and Drill in Some Screws

I decided to put a bolt with a nut in. The bolt had a rounded head with a square shaped handles underneath. Saw of the rounded head for cosmetic reasons. I used one layer of duct tape to secure the cog on to the bolt (don't use super glue if you are looking to dismantle this in the future!)

As you can see on mine there are a lot of gaps where the pellet can and will get jammed. So the best option here is to get small pieces of plywood and sand it down until the pellets revolve without any problems. (If you have a coping/ban saw then ignore the last sentence)

Now we want to put the front face panel on.

QUICK TIP: You can actually drill a pilot hole with a nail. It saves you from breaking those thin drill bits. Try it you won't be disappointed!

Once you have drilled to the desired depth, you can start screwing.

Step 4: Quick Overview of the Magazine and What Next!

As you can see the whole device is just under 4 CM (1.5").
The magazine is somewhat gravity fed.
I would take this time to start sanding and smoothing down everything. I bevelled the front and back of the magazine to make it easier to install on to my gun. Also keep an eye out for the bolt on your gun. the cut out on the magazine must sit firmly in place and leave enough space for the bolt to cock smoothly.

Step 5: Finish Up!

Once you have everything sanded down. You can start painting. I used this rubber effect/textured paint. This gives it a non-gloss finish and is durable.

Last you will need to glue the nut on to the bolt. I used super glue. It fits on tight and allows me to rotate the cog and load the next pellet. You can use two adjustable wrenches to remove the bolt if needed.

All I have to do now is drill a hole on the side parallel to the pin on near the pellet tray and get a long enough pin to hold the magazine in place.

So I spent max £15 to make this (I still can make two more magazines). Instead of paying £50-60 on just one.