I've only very recently started to seriously look into US optics so forgive me for my ignorance! Ive read that US optics used to offer custom tube diameters in 30,34,35 and 40. most of where I've read this is in reviews from a few years ago. Longrangesupply.com allows for custom options and has the custom tube diameters listed but i haven't found anywhere else that has these. does US optics still offer these options? can a larger tube be had on any model?