I think we need to define the term "flop". A flop is a cartridge that NEVER caught on. The 22 WRF is not a flop; it was very popular once but was replaced by the 22 Magnum. The 30 Carbine is certainly not a flop; it's extremely popular, sells millions of rounds each year despite having only one main platform (in addition to the Marlin 62 lever action).
The 9mm Federal, the 256 Winchester, the 22 Jet, now those were flops.
I agree. Flops NEVER caught on. Hard to say the 45Gap was a total flop when thousands of LEOs carry it every day. Same with the 30 carbine. Tens of millions of it was manufactured and it still sells.
On the other hand, and I am about to contradict myself, onother way to look at it is loss of investment. In this light the 45GAP may be a flop when you factor in the R&D, machining, and marketing costs Glock put into that round. The same could be said for the 327 Federal and possibily the .357Sig although the jury is probably still out on tboth of those. But Winchester had to have lost their ass on the WSSM lines.
Two others that I have guns chambered for are the .375Winchester and .222 Rem Mag. Two very capable rounds that went nowhere. Bad timing and redundancy hurt the .375 and losing out on government tests killed the .222Mag.
In the end, effective marketing delivering a perceived advantage is probably more important than providing an actual improvement.
Good thread.