Might be moving a little off topic, so forgiveness sought. The " Bob" .257 Roberts lost popularity for another reason: The case size is an odd length. It is made on the excellent 7x57 Mauser case. So is the 6mm Remington.
This is a mid-size case, as far as length is concerned. It will not work through a short action bolt gun. Too long. A regular full length standard action rifle is unnecessarily long, heavier and has longer bolt travel, and wasted magazine space.
There are only a few rifle manufacturers who continued to make bolt guns with a so-called mid-length action. I have a rifle built on a SAKO L-579 action, a true mid-length action. It is chambered in 6mm Remington (actually barrel stamped .244 Rem). The action is long enough to handle the 7x57 class of cases, without being heavier and having longer bolts and longer magazine well and magazine as would a full length standard action.
These are no longer popular, due to the proliferation of short action rounds that perform just about as well, or perhaps better sometimes, especially the short action magnums which seemed to be in vogue for a while.
There are real advantages to these mid-length rounds. They have the higher efficiency of the short action rounds, like .308, .243, .260, but have higher powder capacity and therefore greater velocity potential, especially when hand loaded. But the x57 cased rounds seem to have gotten lost in the shuffle. Pity.