AVRDude not in sync: resp=0x00 AtMega328

I've breadboarded what is essentially an Arduino Uno. I've loaded firmware onto an AtMega 8 and the computer recognizes it as an Uno in COM12. I've uploaded optiboot to an AtMega328 (read: not AtMega328p) and set the fuses to Extended: 0x05, High: 0xDE, Low: 0xFF.

I've added support for the AtMega328 in the avrdude preferences file. When trying to upload the blink sketch, I get this error:

         Using Port                    : \\.\COM12
         Using Programmer              : arduino
         Overriding Baud Rate          : 115200
avrdude: Send: 0 [30]   [20] 
avrdude: Send: 0 [30]   [20] 
avrdude: Send: 0 [30]   [20] 
avrdude: Recv: 
avrdude: stk500_getsync(): not in sync: resp=0x00

avrdude done.  Thank you.

Any ideas? I've triple checked my connections and tried selecting all the different boards. I can upload to the chip without the bootloader using ISP headers just fine.