how to change O-rings in WA style M4 mag

[swannie_2006]

Hello all,

I have a few Bopmber and WA mags that I need/want to upgrade to take green gas. I bought the G&P O-rings.

I have a problem, though. I am able to change 2 out of the 3 O-rings without any problems and I can re-assemble said parts but one is just a real PITA. That certai O-ring is highligthed in red in the photo: WA mag disassembled

 

I put on the new ring but that is somewhat thicker than the original thus it is impossible to insert it back into the mag body and put back the pins as well. How did you guys do it without breaking the mag or the mag ?

 

thanks