Q: The only difference between the two is the amount of cast on the stock and the spare carries noticeably more than the other. Should I have it reduced?
A: My inclination is to say yes, have the work done, especially as you are so used to the dimensions of your first gun and, possibly, had it fitted some time in the past.
Then again, if it hasn’t been fitted to suit, who’s to say the new gun isn’t a better fit, and the old lass is the one in need of some remedial work!
On balance of course you should have the newer gun altered but don’t forget that lots of shooters – and you might be one of them – gradually adopt a stance and style to fit themselves to the gun, not their gun to them.
If you are happy with the way things are then by all means keep on doing what you’re doing but if you have a few lingering doubts it would be well worth seeking the advice of a professional fitter.
You might also want to fire both guns at a pattern plate from a distance of 15 yards to determine how the different amounts of cast affect pattern placement.