I have made my 10 round mags out of a lowcap . Jou have to cut the mag off and cut some flaps out now you take the flaps and heat them till they glow. Now you have to bend them over the bottomplate of the mag and beat them down with a hammer . The inner of the mag has also to be cut . Cut the Spring and push it into the pipe in the inner of the mag . Close the End of the pipe in the mag with a screw . And so you will have your 10 round magazin.
If you have problems with my english i am sorry couse my english is a litle bit rusty ^^