Primer strike from chambering

[AndyLate]

Pardon my ignorance, but wouldn't every round that is cycled into the chamber get dimpled like this right before you pull the trigger? Why just the first round?

Of course they will. But it's the top round in the magazine that gets chambered, ejected, and reloaded multiple times.

Andy

[Uni-Vibe]

Of course they will. But it's the top round in the magazine that gets chambered, ejected, and reloaded multiple times.

Andy

Same thing with pistols. That first round keeps getting loaded, and eventually bullet setback can occur.

Lawman I know says SWAT doctrine is to discard any AR cartridge chambered and not fired.

[26 Inf]

Same thing with pistols. That first round keeps getting loaded, and eventually bullet setback can occur.

Lawman I know says SWAT doctrine is to discard any AR cartridge chambered and not fired.

That isn't uncommon in many agencies with actual patrol rifle programs.

[T2C]

Same thing with pistols. That first round keeps getting loaded, and eventually bullet setback can occur.

Lawman I know says SWAT doctrine is to discard any AR cartridge chambered and not fired.

We expended carry ammunition and issued new duty ammunition annually. We have never had an issue with ammunition that was not exposed to large quantities of moisture.

[ThirdWatcher]

Same thing with pistols. That first round keeps getting loaded, and eventually bullet setback can occur.

Lawman I know says SWAT doctrine is to discard any AR cartridge chambered and not fired.

Same policy for Patrol when I served in LE. Once a round is chambered it is either fired or it joins the Range ammo pile.

[26 Inf]

I took these examples from a handout:

1) This past fall, a large SWAT team here had a failure to fire from an M4 with (redacted) ammo during an entry--fortunately no officers were hurt and the suspect immediately threw down his weapon when the carbine went click instead of bang.

The round from the potential OIS incident had a primer strike of only .013"—the minimum firing pin indent for ignition is .017". In addition, the primers on the other rounds were discovered to have been damaged from repeated chambering. When the same cartridge is repeatedly chambered in the AR15, the floating firing pin lightly taps the primer; with repeated taps, the primer compound gets crushed, resulting in inadequate ignition characteristics--despite what appears to be a normal firing pin impression.

2) From 1965: A soldier in the 82nd, during the operations in the Dominican Republic, chambered a round while preparing for guard duty that had been chambered and ejected several times. His weapon discharged, though it was on "SAFE" according to witnesses at the scene. The soldier was negligent about where his weapon was pointed and the round killed a local child.

The soldier was court-martialed and acquitted. Investigators were able to repeatedly duplicate the incident by chambering a round from the magazine several times. They discovered that this malfunction, firing when a round was chambered, could be duplicated at around 10-15 chamberings. They also found that at about 10-15 chamberings, many rounds did the opposite and the primers became desensitized enough that the rounds would not fire.

3) ……I went through my duty ammo and pulled a couple of rounds that were dimpled. I took one of those and loaded it a total of 13 times then fired it. I pressed the shot heard a click...Boom. The delay was quit short, less than a second, but noticeable. I have heard of this, slow burn, but never experienced it before.

[Uni-Vibe]

I've fired once-dimpled 5.56 with no ill effects. Interesting that 26Inf can duplicate the problem by a dozen or so chamberings.

I take my carry 9mm pistol down for a de-linting and lubing about every 4 weeks. I discard the load that's been in the chamber and use a new round. The previously chambered round gets put in with the range-fodder stuff for a proper cremation at the next range trip. This avoids the possibility of bullet setback with repeated chamberings.

[RHINOWSO]

I'll rechamber pistol ammo a number of times, but AR15 only once unless I'm at the range and can expend it (unloading for cold range, unloading, etc).

[LMT/556]

I only slow load an AR to pop the random groundhog out back, if I don't get the shot I'll unload it, only downside is the barrel extension leaving scratches on the unloaded round.

[XUSMICO]

True but the design calls for feeding from the mag or clip (M1) All I know is I have had to fix more AR extractors where shooters have to load heavy long ogive cartridges by hand one at a time.