What does 'HMR' stand for anyway?
Hornady Magnum Rimfire.
Lots of misinformation floating around here. The 5mm Remington Magnum was NOT on the .22 Magnum case it used a totally separate case and was in its day my favorite for target shooting as the gun and ammo for it were absolutely unreal accurate. It was the first rifle I ever owned that truly deserved the title of tack driver. One day after shooting my target I decided to see if I could hit the four tiny tacks I used to hold it on the cardboard backer. In four shots all four were hit. It is also the first rifle I ever intentionally hit a fly on the target with.
It was NOT a good squirrel or rabbit round unless you confined the hits to the head which if you did would promptly disappear when hit. I bought mine at the Woolsworth store in Talladega, AL (yeah the same town the race track is named after) right after they first came out. I also bought a scope to go on it. I took it up to the nearby Talladega National Forest to the area I hunted in those days and mounted the scope and sighted the rifle in.
Shortly after I walked into the woods squirrel hunting I saw one a long way off. My guess is around the 80-100 yard distance from me in the top of an ancient old oak tree with a trunk diameter of over 4' and perhaps 100' tall. I got a solid rest and aimed at the head which was about all I could see at the time.
I then walked down to see what damage I had done. When I got there a squirrel ran down the tree and stopped on the side of tree for a moment. I quickly shot it hitting the ribs on the shot. The squirrel was literally blown from the tree into and onto a nearby dogwood tree. When I walked over to it there was guts and stuff hanging all over the place. To that day I had never seen such mayhem as that round inflicted on that squirrel. I picked up the pieces and noted a tiny 5mm hole neatly punched thru both ears of that squirrel which was from my first shot. The bullet had gone slightly high at that range hitting the ears not the head.
The squirrel was totally destroyed by the shot to the body. There was nothing to take home to eat. From that time on I knew that if I wanted any squirrel to eat head shots only must be taken.
To describe some of the damage I've seen it do let me list these examples.
1. A squirrel hit slightly off center that was running toward my call on a fallen tree. I hit only the front leg on one side and it took off that leg and then went on to hit the back one and remove it as well. the squirrel died instantly hit ONLY in the two legs on that one side. The entire body on that side was so blood shot the squirrel was barely fit to eat.
2. A chipmunk shot at about 50 yards totally evaporated. The ONLY part I could find was one tiny little leg and it was completely lacking any skin on it. The rest of the animal seemed to have just evaporated as no amount of searching revealed any additional body parts.
3. The first bird shot with it was a starling sitting on a power line wire. Distance was perhaps 25-30 yards. No pieces fell from that bird only some feathers floated in the air and fell to the ground. We saw no chunks of any kind fall.
The round was super accurate in the Remington rifles made for it but it was not a small game round. It was a superb target and varmint round but was horribly destructive of eatable meat on game animals. As much as I like the .22 Magnum it's destruction is mild in comparison to the old Remington round.
The new incarnation of it uses a much differently constructed bullet of less weight at higher velocity. The cost is out of site as far as I'm concerned. I'd love to see Remington make the same ammo using that same bullet again at a reasonable cost. From the prices I've seen quoted it is running on average about double the cost of the .17 HMR ammo. As good as the original was I'd not likely pay that much for it when you can get cases made for it using centerfire primers and reload it yourself. The company selling the cases also sells dies and converts the old Remington rifles to fire the centerfire ammo.
I guess even tho the old round was a favorite of mine I'll stick to the .22 Magnum or the .17 HMR rather than go with the remplacement round now being offered.