In order to run the CTR with T3 mags, you need a magazine retaining clip. Its the little thin aluminum shim that attaches to the trigger and locks the T3 mag into place. I lucked into finding someone doing the opposite - going T3 to CTR, and didn't need the retaining clip.
I'll send you some photos, or just start a fresh thread, once I have the CTR barreled action moved over to a T3 stock. Takes a little opening of the barrel channel, but other that that and the retaining clip, its an easy swap around.