My WASR-10 has proven to be an excellent shooter and I decided I was going to use it for Missouri's firearms deer season. MO requires that any firearm used for that purpose be limited to a maximum capacity of 10 + 1 rounds. A couple of weeks before the season opened, I searched a gun show & called my local gun/pawn shops in search of a 10 round 7.62x39 mag. One of the gun shops had one, so I picked it up & headed home thinking my problem was solved. Not so much... it turned out to be a SAR-3 mag for .223. Just my luck.
Now the simple thing would be to order a 10 round mag, from Brownells; but I wanted to add some things to the order and of course it was too late to get it by opening day, anyhow. What I did have was several eight-buck Tapco mags and some Yankee ingenuity. I tore one of them down, got out my Jethro Bodine cipherin' tablet and arrived at the conclusion that the 3rd rib on the magazine would be 10 rounds or less. Then I drilled a 3/16" hole through the mag body, reinstalled the guts and plugged a brass machine screw into the hole, installed two nuts and cut the screw off flush with them. A little blue Loctite keeps the works in place for the time being.
The result was a 7 round magazine that works fine. The brass screw makes it easy to show Mr. Possum Cop that the evil Commie rifle is in fact legal and suitable for slaying the King's deer.
After hunting season passes, I'll remove the screw and have my 30 round mag back. A couple of wraps of electrical tape will cover the holes & keep earwigs and gremlins out of my magazine.