I have a Mk3 S10 Bull Barrel in .22 which I love. It's extremely accurate and very well engineered, the only thing I would like to do to further imprve it will be to have it blueprinted by John Bowkett and while he does it, have the optional large bolt head fitted. From what I understand from this forum, this greatly improves this already excellent gun, providing more consistency, accuracy and shots per charge. From what I understand, he charges around £75.00 for the work and a further £15.00 for the oversize bolt, traded for the original item.
I seldom shoot over distances greater than 40 yards, and within this range it is deadly.
My personal choice of pellets is for this gun tends to be one of the JSB type pellets, AA, Daystates, JSB themselves, or my personal favourite, RWS superfields. after experimentation, mine is at it's most efficient using pellets with a larger head size, it's preffered diet being 5.52.
I hope this helps and that you enjoy your new purchase, I for one will always keep this rifle.
Regards
Paul M