Thompson m1928 High cap Drum Mag.

The magazine is a High Cap mag that holds around 400-450 rounds. It looks as if it os huge, but most of the space in there are not used. The magacine could be modified to hold allot more but it would require that you make a new feeding line from the mag wheel to the mag bulit exit hole. But I can explain that better when you see the inside.

First thing to doo is to remove the windup handle. And this handle is also the first problem with the gun. If you wind the handle the worng way round the mag can break! Most of the time it results in parts comming loos, so folowing this guide you can open and hopefuly fix the problem.
To remove the handle pull up on the small tab and slide off the handle. Underneath the where the winding handle was there is a retaining clip. Remove this locking clip. Then turn over the magasine so that you can see the small retaining lock on the other side and remove that as well. Be carefull when removing the retaining locks. They are made of metal but can snap if to much force is applied. If they break they are VERRY hard to replace! Now you can take off one half of the metal casing. You can also remove the middle pin (Witch is used to wind up the magasine).

On the other side of the Magacine (Where the charging handle was) there is a small round plastic gripper, that the winding handle attaches to and that has some teeth that grip the inside of the magasine. Pull out the small gripper. Now you can remove the secons half of the metal case. And now you are left with the plastic inside of the case. Remove the 5 screws thar holds the 2 plastic casing sides together. Then jently pry the 2 peases from eachothers lifting them slowly and with little force so you don't break anything. Inside in the middle the main cranking gear is loos and can be removed by hand.

Now that you are inside and has removed the first cranking wheel you can see the 2 internal parts that make up almost all kinds of High cap magasines. The feeding assembly, and the feeding tupe. The feeding assembly has a spring inside, that can store the tension, and that feeds the bb's into the feeding tube. On the back of the feeding assembly there is a lock pin, and 2 screws that hold the assembly together. I don't reccomend opening the feecing machanism unless this is your last option because if the spring uncoils it self you may neaver get it back together.
But if you have to get in there to fix some issues then remove the locking circle and the 2 screws and you are in.

That's it.
Now you know how to open your magasine.
But wait .. What about making room for som extra BB's?

This mod is NOT easy! And if you mess it up your magasine is not going to work. There is no way back because you need to cut off the mounting holes for the screws. But it you succeed you can increase the size to around 800 bb's.
This is how you do it:
1: First you must remove all the old mounting holds for the feeding assembly, and for the feeding tube. (Use a dremmel tool to remove them.)
2: Then relocate the feeding mechanism lower down and slightly rotated. (You have to glue it in place or glue nut's to the frame so that the screws can mount into the nuts)
2.a: You have to make sure that when you place the feeding assembly the main drive wheel that is supposed to fit in the middle will grip the feeding wheel.
3: Make a new feeding line that will take the bb's from the feeding mechanism out of the magasine top.
As you can see it is NOT an easy mod! So only attempt it if you have you are a bit of a handy man. And be aware that it's not possible to just go back to the original placement because you have to remove the mounting holes!.
I have attached a concept drawing of how you can make it.