I seem to recall that one reason only Remington ever produced rifles for the 5mm was that it operated at much higher pressures than the .22 WMR. Remington had to redesign their extractors to avoid rim blow-outs and other makers just were not interested in producing a whole new gun just for a round with very limited sales appeal. Today, with dozens of guns in .22 WMR and with every maker jumping on the .17 HMR bandwagon most folks don't realize that fifty years ago the .22 WMR got off to a very slow start. Gun writers of the time did not sing the praises of the new round but were quick to point out that it was not as accurate as the .22 longrifle and that ammo cost five times as much and that you could reload a .22 Hornet for less than the cost of .22 WMR ammo.
For many years only Winchester produced the ammo and the only rifles available were the Winchester pump and the upper barrel of the Savage m-24. Mossberg introduced their "Chuckster" in .22 mag and Marlin began offering bolt actions in .22 mag and CCI began producing ammo which was a bit cheaper than Winchester and slowly, very slowly, it began to build momentum. Even in the seventies, 20 years after its' intro, there still were just a few rifles offered and still only two ammo choices, Winchester and CCI, all in 40 grain weight, FMJ or JHP. I really believe that Ruger kept the .22 mag alive during the early years by offering the Single-Six with interchangeable cylinders for longrifle or mag. It's only in the last 10 or 15 years that the .22 WMR has really taken off. So it's no mystery as to why the 5mm Remington failed and I think the same reasons may count against it today, except that today the gun writers would play it up big time, just as they do everything produced by anyone who buys add space.
