Square Propeller

I am converting some propeller over from some FS9 AI aircraft to FSX.  In most cases the process is fairly straightforward.  However I rand in to some RFAI Rockwell 112 two-blade models that didn't have a propeller texture. 

I tried two textures from a different source, but ended up with square propellers even though the images work great with the aircraft the I borrowed them from.

Any suggestions on how to eliminate the corners?

Thanks,

Ernie