Does not fit all ak47’s - Truglo Tritium AK-47 Green Tritium W/White Outline Black TG231AK1

I purchased for my palmetto state arms psak47. The included drum is too small for my ak. It just slides in and out with little resistance. Other than that seems to be of good quality, and the tritium glows fine in low light. Maybe I received a bad piece? Or maybe my psak has slightly out of spec front post, I’m not sure because the oe drum is fine.