Lucky for me the 17 HMR doesn't develop the case pressure of its center fire brethren, otherwise I could be looking at a lot more destruction and potential injury.. And in getting near 40 years of shooting, this was my first blow up (darn sure hope I don't have another one for at least another 40<grin>).. But I wanted to post this in case anyone else is shooting an AR set up for this powerful little rim fire round..
Having been recently upgraded by the factory with all of the latest modifications, I was shooting a factory AR upper, chambered in 17 HMR.. It was sitting on a billet lower with a Timney trigger, and the factory recoil spring assembly.. (The original owner put the muzzle brake on this little thing.. As if a 17 really needs a MB<LOL>.. Anyway, I like the way it looks so, perhaps the guy wasn’t so silly after all <grin>.. And yes, the scope base has also been swapped around)..
Anyway, I had been having intermittent failures to feed problems with the bolt not stripping the top round of the magazine, but rather moving it slightly forward, and then crushing the heck out of it.. The jam could happen as you let go of the charge handle to load the first round, or on any round then auto loaded.. In fairness to the manufacturer of the upper, they recommend stock trigger for best results, and since I was not using a “stock” trigger, I was not getting “best results”.. I was trying different brands and bullet weights to see if any would work better.. And I was finding Hornady ammo worked the best of what I had tested thus far.. And then I noticed if I held the magazine forward slightly.. It would have less of a tendency to crush the top round.. I went back to the ammo which seemed to jam the worst (about 5% failure rate), and I fed 2 magazine without any failures (note my tests are 5 rounds into the 10 round mag’s)..
I feeling pretty good that I had been able to work out the jams.. But then what happened next I was not expecting.. I pulled the trigger on the 2nd round from the magazine, and the sound of the report was significantly subdued.. Also I could see traces of smoke coming from area around the receiver you normally don’t see smoke.. Seeing smoke where you don’t expect to see it is normally the first indication of something “not good”..
I remove the magazine, and notice it had be split apart, and the front of it appeared to have been cut.. I look into the action, and notice the bolt was not all of the way forward, and there appeared to be something in front of it.. I drew the bolt back and the ruptures on the case were obvious.. When I first looked at the case, it appeared the neck had been blown off But looking more closely, the neck all there, it was just blown out.. Basically, the gun went off without the case being completely in the chamber..
It was clear the case failure was caused by the firing pin being able to strike the rim without bolt being into battery.. For some reason, the case got stuck going into the chamber, leaving the case head unsupported..
I think this is kind of unsafe and intend to discuss it with the manufacturer.. But I did want to warn anyone who has a 17HMR to be careful with it and please always wear eye protection..
Checking for grins and giggles, sure enough the bullet was in the barrel.. With a cleaning rod, I drifted it out.. The upper now sits on a lower with A2 stock and stock AR15 trigger group.. I have put 10 rounds through it since moving the upper, and have not seen any further jams.. I also check to make sure the bolt is fully into battery before I pull the trigger.. I will probably do this for a long time..
No announcement yet.
WARNING !! 17 HMR blow up
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