Since the subject of slam firing has been in the headlines recently, I thought I'd touch on the subject. I've corrected the issue in several pistols over the years, and learned a few things about it in the process.
First...slam firing doesn't happen unless the hammer falls in the same way as it does when the trigger is pulled.
About 20 years ago, I got a call one Friday afternoon from a young guy who was experiencing hammer follow problems with his Springfield Mil Spec. Cock the pistol and pull the trigger...and the hammer followed the slide all the way down every time. I pretty much knew what it was and told him to bring it by the next morning. The disconnect wasn't disconnecting.
Thinking it was either a worn disconnect or a spec issue with the center rail, I didn't suspect the real problem until he showed up...and there it was. The top of the disconnect sat dead flush with the top of the frame. Then, he admitted something.
He'd read on the internet that a man could convert a 1911 pistol to fire full auto by simply filing the disconnect...and it didn't work. He was stuck with a single shot pistol and wanted it to function normally. I replaced te disconnect and all was well. After a short lecture on the illegalities of attempting to create a machine gun, he was on his way.
So, a simple hammer followdown can't cause burst or full auto fire. The hammer has to hold at full cock and then trip. Riding down with the slide doesn't provide enough impact energy to the firing pin to light a primer in a gun that doesn't have a seriously weak firing pin spring or an overly long firing pin, and even then it probably won't.
So, how does it happen?
In every instance that's come to my bench, the cause was a failure of the sear to freely reset with the sear staging on the very tips of the hammer hooks so that the slide going to battery caused the hammer to jar off the sear crown. Because the sear wasn't resetting, the half cock didn't catch it, and the result ranged from a single slam fire to 2 or 3 shot bursts to emptying the magazine. At some 1300 RPMs, 7 or 8 rounds is gone before the surprised shooter can get off the trigger and sometimes even that doesn't stop it.
During such an event, the pistol isn't too difficult to control if the shooter is expecting it. When it comes as a surprise, Everything after the first two rounds goes over the berm.
The causes of the sear failing to reset vary. It can be the trigger dragging in the channel or the top of the disconnect dragging on the bottoms of the sear feet to simply a piece of grit becoming trapped between the frame and the side of the sear. The last one is admittedly pretty rare, but it does explain a pistol that slam fires once and never does it again.
This is the reason that I'm adamant in my advice to never ignore any problem with the fire control group. If it happens one time, get it checked out. Then, retest by loading and firing two rounds at a time until you're satisfied that the gun is fixed.
First...slam firing doesn't happen unless the hammer falls in the same way as it does when the trigger is pulled.
About 20 years ago, I got a call one Friday afternoon from a young guy who was experiencing hammer follow problems with his Springfield Mil Spec. Cock the pistol and pull the trigger...and the hammer followed the slide all the way down every time. I pretty much knew what it was and told him to bring it by the next morning. The disconnect wasn't disconnecting.
Thinking it was either a worn disconnect or a spec issue with the center rail, I didn't suspect the real problem until he showed up...and there it was. The top of the disconnect sat dead flush with the top of the frame. Then, he admitted something.
He'd read on the internet that a man could convert a 1911 pistol to fire full auto by simply filing the disconnect...and it didn't work. He was stuck with a single shot pistol and wanted it to function normally. I replaced te disconnect and all was well. After a short lecture on the illegalities of attempting to create a machine gun, he was on his way.
So, a simple hammer followdown can't cause burst or full auto fire. The hammer has to hold at full cock and then trip. Riding down with the slide doesn't provide enough impact energy to the firing pin to light a primer in a gun that doesn't have a seriously weak firing pin spring or an overly long firing pin, and even then it probably won't.
So, how does it happen?
In every instance that's come to my bench, the cause was a failure of the sear to freely reset with the sear staging on the very tips of the hammer hooks so that the slide going to battery caused the hammer to jar off the sear crown. Because the sear wasn't resetting, the half cock didn't catch it, and the result ranged from a single slam fire to 2 or 3 shot bursts to emptying the magazine. At some 1300 RPMs, 7 or 8 rounds is gone before the surprised shooter can get off the trigger and sometimes even that doesn't stop it.
During such an event, the pistol isn't too difficult to control if the shooter is expecting it. When it comes as a surprise, Everything after the first two rounds goes over the berm.
The causes of the sear failing to reset vary. It can be the trigger dragging in the channel or the top of the disconnect dragging on the bottoms of the sear feet to simply a piece of grit becoming trapped between the frame and the side of the sear. The last one is admittedly pretty rare, but it does explain a pistol that slam fires once and never does it again.
This is the reason that I'm adamant in my advice to never ignore any problem with the fire control group. If it happens one time, get it checked out. Then, retest by loading and firing two rounds at a time until you're satisfied that the gun is fixed.
