Okay. I found what I believe to be the solution. At this point, this is for anyone who does a future search for:
155 grain truncated cone hard cast bullet in 40 S&W failure to feed.
This particular bullet has a sharp shoulder. I believe a wider bullet head or longer bullet would contact the inside of the chamber sooner to aid in feeding by creating a less steep angle during feeding.
Increase the OAL as much as possible while still
1) chamber properly still head-spacing on the case mouth, bullet does not touch rifling. Tested in 2 ways - one rudimentary way is dropping finished round and listening for crisp "clunk" of impact against brass case mouth, not of a softer sound of lead against rifling. Second way is by inserting bullet into chamber until stops, then measuring remaining space with caliper from the back of said bullet to the back end of barrel hood extensions. Adding the two numbers gives your maximum chamber length but does not take into account the next requirement below...
2) be short enough to fill up magazine without binding / slowing down feeding.
My OAL is now 1.170. They feed well by hand cycling. The brass is no longer dented after cycling but there is a shiny spot from impact against the bottom edge of the feed ramp.
I don't think I'll be buying any Truncated Cone with a sharp shoulder anymore. I'll look for something rounded.