iPhone 3GS rerestore 6.1.2?

Before i blow my brains out trying to figure out if this is possible could I have your suggestions..

My iPhone 3GS is currently running 6.1.2 and I wanna rerestore 6.1.2 to the default settings, I have tried with a default ipsw but it comes up with the 'device is not eligible' error, also in DFU mode it doesnt want to restore.

I have a slight doubt as I haven't saved the blobs for 6.1.2 so im guessing that makes this impossible to accomplish?

thanks guys in advanced :)