You know what they say..."everything in Texas is bigger"
a Texas penny is made by hammering a penny between two pieces of leather such as a belt..
The hammering flattens the coin without distorting the devices if done properly...the' flattening 'of the coin causes the copper coating over the zinc core to split off leaving the the dull grey of the zinc remaining...and the larger looking disc is now a 'Texas penny'
at least that's how it was explained to me, hope that might help