This cartridge was brought up in a post and again in chat so I thought there might be some interest in it.
While the .204 Ruger is certainly not the first .20 cal
(5 mm) cartridge it most certainly with Ruger's backing be the one that makes the grade and lasts the longest.
Way back in time there were two 5mm (.20 cal) pistol cartridges. The 5mm Clement Auto and the 5mm Bergman. They were center fire auto pistol cartridges that were designed for very small automatic pocket guns. Obviously they were for noise value rather than stopping power. Or perhaps to shoot a in-law that you didn't really want to kill but just to let them know you were angry.
A later 5mm cartridge did have a measure of success here in the States. The 5mm Remington Rimfire Magnum. With only two rifles ever chambered for the cartridge (and a T/C pistol) it died on the vine. It shot a 38 gr bullet at a muzzle velocity of 2,100 fps. In it's time it was the hottest rimfire cartridge. It was a good idea but didn't catch on or have the backing of the other gun manufactures.
But now the King of the gun manufactures comes along with a center fire cartridge that is a screamer. It is at this time the fastest, hottest commercial rifle cartridge to ever come out of a factory. Shooting a .20 cal. 36 gr. Jacketed V-Max (Hornady) bullet at 4225 fps from a 26 " barrel it instantly disintegrates anything it hits in the way of varmints. For larger prey such as coyote, it makes a very small hole and no exit. The fur hunters are going to love this one. The Hornady bullet was produce by the factory a few years ago for wildcatters and then Ruger got into the picture. The cartridge they came up with is basically a .222 Rem. Mag case necked down to .20 and with a shorter neck. Good idea on the neck. The bullet is shorter than the .223 bullet that the Rem Mag used so why have all that extra neck? It increased powder capacity and added extra FPS on the advertising hype. It also prevents the cartridge from being chambered in other .222 chambers. Although there would be no danger just a hollow sound as the bullet free bored down the barrel and fell out on the ground.
Ruger has chambered three bolt action rifles and two single shot rifles for their new baby. All were good selections. The Model 77 MKII in blue and stainless, and a KM77RLFP Ultralight All-Weather in SS. The KM77VT Target rifle is a good choice for the accurate little cartridge. The Ruger #1 standard and the #1 Stainless Varminter will get the chambering. All these guns are scheduled to be available in March 2004. So start saving your nickles.
Hornady loads the cartridge with 31 gr. of a canister ball powder and it is a compressed load. Handloaders may have to settle for less in the way of performance as at this time there is no commercially available powder to match the special Hornady powder. Accuracy per Rick Jamison Handloading Editor for Shooting Times Magazine is excellent. With 3 shot groups going into .3 inch and 5 shot groups at .8 inch with even a 10 shot group not exceeding .9 inches. Time will tell how the rifle barrels hold up with this hot number. The 220 Swift had problems in the area but it was old technology. The new steels and better manufacturing techniques may make the difference with this ultra modern round.