"From everything I've become aware of the trend seems to have slowly slid up into larger calibers over the decades...as an example, T/C finally discontinued its once popular .45cal...compressed its focus onto the .50 and .54cals and that's what they had available for quite a while...then added the .58cal on top"
I think you are correct Roundball, I can recall the early '70's when .45 and .50 were the norm, along with all the modern do-dads to go with ML's that have emerged over the years magnumitis has taken a good hold as well.