If Cornyn gets a 100% rating from the ACU, then their numbers are screwed up.
As President George W. Bush consolidated his power over the Republican majorities in both houses, voting in Congress has changed more dramatically than any time since the American Conservative Union has been measuring the legislative process in America. The ratings for 2003 show a dramatic lowering of the conservatism scores for Republican members of Congress and the liberalism scores of Democrats declined too. The overall result has been a strong shift in Congressional voting to the middle, presumably where the president wants to be politically facing an election this year. But the cost has been a rapid increase in government spending and a decline in conservative voting generally.....The pattern is best illustrated in comparing the House ratings in this and the preceding years. In 2002, 60 House members scored a perfect 100% conservative rating (compared to 37 the previous year and 28 the year before), while only two had perfect scores in 2003, Mike Pence (IN) and Zack Wamp (TN).
http://www.conservative.org/vicechairsummary.asp