We just read on WTA that there has been another KB with a Semi-Auto .17HMR rifle. Most of the time the result of a KB is only stings and scares… but this time the shooter was hurt badly.
A blow back semi auto .17HMR (and even the .17 Mach 2 but to a lesser extent) is a bad idea. No matter who makes the gun or how custom the gun is…. it’s going to, at some point, have a KB. This is the same problem with EVERY semi auto .17. Which is why all of them have been recalled and dropped from production by everyone that has ever made them. Except for Alexander Arms, who is making a 1200 dollar AR type – that will still do the same thing everyone else’s did. Even in one of the Gun Rags, during the review process the writer mentioned this happening but kept shooting it.
There are a couple causes of the .17 Rimfire KB’s.
1. The bolt, rebounding off of firing the last round, slams forward into the cartridge rim hard enough to set it off while the round is in the magazine.
2. A few rounds fires slightly out of battery puts enough carbon fouling in the chamber to builds up until a case is completely unsupported and firing pressure blows it.
A successful .17HMR Semi Auto design needs a locked breach – which is why most .17HMR brass from a Semi show the case head to be mushroomed out. The bolt isn’t holding it in and it’s opening too soon. The bolt will have to close on the round and lock it into the chamber, just like a bolt action rifle. It also needs a speed controlled bolt so the bolt doesn’t hit the case head too hard. To accomplish this, the rifle will need a Linear Electric Drive to cycle the action via electric power instead of by Blow Back. The technology to build an electric linear drive is out there. We’ve been using them for years in other applications. We just need to make it smaller and put it into a rifle.
Until that time… Do not fire any – ANY – Semi Automatic .17 caliber Rimfire guns. Because at some point, the thing will KB and someone will get hurt.
I remember when Magnum Research first started dealing with this problem… and still to this day… blame the Ammo Makers for making .17HMR ammo that was “too hot”. But this is intellectually dishonest because if you are going to build a gun for any caliber, it needs to be able to handle that caliber. Hornady, Winchester, Remington, CCI… out of a bolt action rifle, when fired over a Chrony, we find very consistent velocities. Which is one of the reasons the .17HMR is such an accurate round. The ammo isn’t the problem, I don’t care what Magnum Research says. When I talked to the guy there on the phone with Magnum Research, he went on about pressure spikes and that it’s all the Ammo Maker’s problem. Well, everyone else had already started dropping and recalling their .17 Semi’s… and these guys were still blaming Hornady. Then they blamed CCI, and Winchester. Finally they issued a recall. You send your gun back to them and they rebarrel it to .22 Magnum, like it or not. This isnt cool in my book. You didn’t buy a .22 Mag, that’s not what you wanted. They should issue Refunds. This is one of the reasons I really dislike Magnum Research. They have impressed me as being really shady over this SNAFU.