Will overfilling my 310cc saline implants make them harder?

overfilling  a saline implant will reduce the risk for post operative rippling , but will make them more firm and will distort the shape of the implant to be rounder and more ball like rather than a disc. Overfilling also increases the risk for rupture later, particularly if you go significantly beyond the recommended fill volume.In the past, when saline was the only product on the market, many PS would overfill to try to reduce rippling. I would be interested to know why you are considering saline implants. The advantages of gel implants outweigh the saline,

Overfilling does make them firmer, but also prevents rippling to some degree.  There is also a saline implant called the Ideal Implant which is softer and has less rippling which is something that you may want to research if you are doing saline....  Good luck!