Voltage offset and fluctuating output in transimpedance amplifier circuit
Why might it be that for nearly 20 of the same OPA227P chips, the
  voltage offset is about .5V? I checked the chip's datasheet and its
  offset should be 75 uV maximum. The chip is in the PCB, no input,
  powered by a 12 V source, grounded to a metal table... how can this
  problem be fixed?


First off... A floating input is not a good way to test a circuit. If you want to check the input, then ground it. This is how texas instruments tests for voltage offset. (by switching s1 and s2 on as shown below)

 
Source: www.ti.com/lit/an/sloa059/sloa059.pdf


  And, why is the voltage output that I see not stabilizing on a single
  value? It fluctuates up and down a lot and is generally a lot lower
  than expected, the gain is lesser on a magnitude of 10-100. Is there
  something that I can do so that the voltage output stabilizes? Why
  might the gain be so lower than expected, is there something I could
  do to remedy that?


Because the input is floating! If you look at the output, it's most likely outputting a sine wave at 60Hz. The input bias current is 1nA for this part, with nothing driving the input this amplifier could pick up a lot of noise from many different sources. (if your input isn't floating, then you probably haven't shielded your current source very well from noise)  

If it's not 60Hz the amplifier is picking up and you only have a gain resistor then it may be that the amplifier isn't compensated. You need some capacitance to compensate the amplifier.