Do you need the 12 at the back?
OP probably doesn't (witha 50t large chainwheel) and I only use it because it's there. But
@User , please link to a 13-27+ cassette (any speed). You can get 13t smallest sprocket and compatible lockring, but I think at some cost and not as part of a cassette. The junior ones are all close ratio.
Cross post with the ones above. What
@User has done
@DanZac is to physically split up the pinned together part of two cassettes. And I'm guessing from your other posts this may seem a good idea to you in principle (and it is - a 'custom' cassette, much easier with Campagnolo, of course) but the practice requires expertise which I haven't got, don't know about you. My effort at this is to buy an HG-50 11-30 cassette, ditch the 11t, insert a 13t from a used cassette (the 13t gets little use so will not be worn) and the 14t-30t 7 sprockets are pinned. So at least it goes 12, 13, 14, 16 etc rather than 11, 12, 14, 16 . . . 12 to 14 is too big a ratio change and as I said the 11t is redundant.
