Ditto what he said...!
From something I found on the web:
The 5mm Remington Rimfire Magnum
The 5mm Rimfire Magnum is based on a case similar, but not identical, to a necked-down .22 Magnum case. Its case is a little bigger and it has to be stronger as it must contain 50% greater pressure, 22,000 psi Vs 33,000 psi. Bullet diameter is .2045", or .20 caliber, the same as the .204 Ruger centerfire cartridge.
The Remington factory load drove a 38 grain Power-Lokt semi-spitzer hollow point bullet at a muzzle velocity (MV) of 2100 fps. This offered an increase of about 25 yards of practical range compared to the .22 WMR.
It was introduced in a pair of Remington bolt action rifles, the Models 591 (clip magazine) and 592 (tubular magazine). T/C chambered their Contender for the 5mm for a short time. As far as I know, those were the only firearms available in 5mm RFM. The cartridge was not picked-up by other rifle or ammunition companies.
In retrospect it is hard to understand why the 5mm was such a commercial flop. Its ballistics were quite appealing, as we shall see. I think that the answer is that in 1970 the market was simply not ready for a new rimfire cartridge with an "undersize" bullet. Like the .350 and 6.5mm short magnum centerfire cartridges and Electronix ammunition, the 5mm RFM was too far ahead of its time. If it had it been introduced in 2000 to a more mature market, the outcome might have been much different.
From personal experience... this is one deadly load! I was out critter hunting with my boy and he had his .22-250 and I swear this load opened 'em up as much as his! It is a unique design to itself and do not hesitate to pick one of the old Rem's up! Some had extractor problems which can easily be fixed. This is one fun cartridge and on par cost wise with the .17's and .22 mag. when I purchased over the internet, even with shipping. Plus, it's fun to shoot such a unique cartridge. I have had my Taurus pistol on order for some time and not holding my breath. CZ and I heard Cooper (which would be awesome!) are considering chambering for this round as well.
JUST DO IT!
2nd Part:
I also found some Centurion .22 ammo (made by Aguila - like the 5mm) on the web that I picked up incredibly cheap and it shoots in most of my guns - both pistol and rifle as good as Eley Tenex!! I now use it for my pistol competition shooting - it's awesome! All of the Aguila ammo's are great from what I have seen. The only one to watch is the Subsonic Sniper (SSS) w/the 60 grain bullets. You need the right combo to stabilize it. If you have it - watch out critters!
