Bonneville America Forums Forums Technical Forums General Tech Chain stretch = 317mm - am I getting close?

I'm just wondering when I need to budget for a new chain and set of sprockets. I measured the slack last night and it came to 317mm through 21 pins. The Haynes manual says 321mm is the max.

I've got 15K miles - how many more should I expect out of that last 4mm?

Thanks!