This has most likely been chewed to mash before but I'm relatively new so here goes: I've got a Colt GS SP2 made in 90, shoot it whenever I want, guess State Farm would rate it as " recreational" category, not a "to work and back daily", last week I thankfully had it pointing up, safety off (can't put it on if not cocked) put in mag, pulled charging handle, returned it, pushed bolt release and BOOM!,didn't fire again though. Gun is in excellent shape, very well maintained, mabye 1,000 rounds thru it, since then I always set safety before chambering. I'm retired Army, can't think of how many times I've been on a range with guns much more worn than this one. Never happened. How common is this?  Thanks

rk

I have never actually had a slam fire. But every time I go shooting I will release the bolt, take out the mag and eject the unfired round. I look at the primer and there is a dent there. My guess would be that you just had a soft primer. Everytime I release my bolt now, I make shure my rifle is aimed downrange and ready to fire.

Rob

A couple of things don't make sense to me, if you had the bolt/carrier forward and locked,put in a loaded mag,and pulled back on the charging handle to retract the bolt/carrier to feed a round into the chamber the bolt would have pushed a round from the mag and into the chamber and locked.  You would not have had to activate the bolt release. If indeed you pulled charging handle over a loaded mag and the bolt/carrier stayed to the rear and you returned the charging handle to the forward and locked position.  The question would be why did the bolt/carrier stay to the rear?   Protruding firing pin that hung on the rim of the cartridge?  That might cause a BOOM when the bolt flew forward!!  I don't think that the pin can protrude that much though because of the recessed bolt face.  If you mistyped and the bolt/carrier actually pushed a round into the chamber when you released the charging handle over a loaded mag then the disconnector may be allowing the hammer to follow the bolt forward.  If you have a Ar 15 hammer it should have a relief cut on it's face to make it catch on the head of the firing pin in case the disconnector fails.  This is a fail safe against slam fires.  It probably comes down to what the poster above said, a soft primer.

Putting the safety on will gain you little. That only prevents the rifle from firing when the trigger is pulled and will not effect a malfunction.

Could have been a high seated or overly sensative primer. The dimple in every chambered primer is from free floating firing pin hits which is normal.

If your hammer slipped off the disconnector then parts are worn and need replacing.

I would suggest you pull a bullet. Dump the powder, push the bullet back in the cartridge and feed and chamber that squib round a hundred times to make sure it does not repeat.

What kind of ammo?

Supposedly mil-spec ammo has a harder than normal primer to minimize the likelihood of a slam fire from the floating firing pin.

If you have the empty, take a look at the primer indentation and compare it to a normally fired round.

If the indentation is much lighter, I’d suspect the floating firing pin.  If the indentation is about the same, I’d suspect that the hammer slipped!

If the round was a reload, it might’ve had a high primer.  This would be an especially dangerous possibility since this could cause the AR to fire out of battery.  

Sorry for the confusion, and thanks for the replies. Maybe this will help:

Rifle was unloaded, safety OFF
Bolt pulled to rear, locked, ch returned
Magazine inserted, bolt released
Boom

Sorry I wasn't clear. Several good points though.
These were reloads (mine)
The primers were not extending but not tight,  I sealed them with fingernail polish, this is just target ammo anyway. Have fired several hundred with no problems
Could not find the empty, don't know where it went.
I agree, most likely the primer. Will save these for my other .223, its a NEF(H&R) single shot bull barrel. I really don't shoot the AR that much anyway.

Thanks again

rk