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Hot Weather shooting / hot chamber

Hi all,

I live in Florida and it has been rather hot and muggy lately (yeah, blame it on "global warming"). A few weeks ago, I shot my benchrest 6PPC in a hot afternoon. I didn't really give the rifle any cool down time due to my time constrains and I noticed at around 30 or so rounds, the bolt became very hard to close when I try to load a new round. I thought it was rather strange as the brass have been properly sized. Eventually, after a few more rounds, the bolt would have required a lot of force to close and due to safety reasons, I stopped shooting for the day. I noticed that the barrel was hot, not hot that it burns your hand, but you wouldn't want to hold the barrel for long either.

Today, very hot (high 90's) and muggy. I was trying out a newly acquired Compass Lake Ar-15 that I plan to use for DCM match. I was practicing the timed fire stage (prone, 10 shots in 70 seconds). The first three relays worked well, the rifle shot very nicely. The fourth relay was different. On the 8th round I pulled the trigger, I hear the hammer fall but round did not go off. I then tried to pull the charging handle back, but bolt won't move, it was frozen. I eventually managed to get the bolt open, and noticed the primer did not have an indent from the firing pin, so it couldn't have been a primer issue. I then thought maybe it was the case not properly sized for whatever reason. I then tried another round, pull the trigger, hear the hammer fall, but this time I was able to pull the charging handle back and load the next round. The primer for the bullet that was just ejected has no indent in primer. Then I pull the trigger and same thing as last happened, all the same. I thought this was rather weird, 38 rounds fired, all went very smoothly (like a swiss watch), but all of a sudden the round either gets stuck and the primers with no firing pin strike, all cases should have been sized properly.

When I got home, I started from the "ground up" to try and figure out the problem. Then it dawned on me that the situation I had today was a little like the one a few weeks ago with the 6PPC. Was it possible that a hot chamber prevents a round from properly being chambered? Maybe that is why the AR never fired today because it was too hot in the chamber? I have been shooting for many many years and never came upon this problem. I was taught in the military that a hot chamber was more likely to create a "runaway gun" where the rounds go off since it gets so hot in the chamber.

If anyone has any insight on this, please let me know.

Thank you,

David
 
Howdy David. Did you eventually get your AR firing? Here's what usually keeps the AR/M-16s from firing; Firing pin protrusion. Pull your bolt carrier and bolt out. Push your bolt inwards into your carrier. Now push your firing pin in. Your firing pin should measure between .050” and .060”. It's easier to buy a firing pin gauge and use it. http://www.brownells.com/.aspx/lid=10379/guntechdetail/How_Does_It_Work__Brownells_Firing_Pin_Protrusion_Gauge

Usually, what causes the M-16/AR-15 to do what it did is carbon or other gunk or debris between the firing pin and inside the bolt. Sometimes the end of the firing pin breaks off. Lastly, you could have had a neck or body of a case separate off a case that was extracted and get stuck inside your chamber. I've had that happen with handloads. If you like to run your rounds a bit on the hot side, the case doesn't have a chance to contract when the weapon starts to extract the spent case. That'll rip the case or at least the rim of the case.
 
David,
Your right about hot chambers and "run-a-way" guns although this pertains to machine guns consistently firing long bursts of fire. I had a similar situation with an AR and found the cotter pin that secures the firing pin in the the bolt carrier had broken. Once replaced the problem was curred.

Good shooting, Jim
 

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