Another AR15 chamber question

[andrew]

OK, I didn't get get my chamber gauged or reamed yet, but needed to test fire some Adcom 5.56 M855, so I put my safety glasses on and loaded 20. The ammo was very accurate, and the empties showed no sign of over pressure (I think), no blown or flattened primers, no extraction problems. But, looking at the case necks later, there seems to be the impression of lands and grooves in about the first 2 or so millimeters of the case neck.

I didn't have any .223 ammo to run thru it to compare the cases, but am now wondering if the land and groove marks are an indication that my chamber is in fact .223 rather than 5.56 indicating an issue with the chamber leade.

In other words, does anyone have a spent .223 cartridge sitting around that they could look at the neck rim and tell me if there is an impression that looks like lands and grooves?

[msbcomputer]

I just checked a few from the other day and there are no marks at all.

[karcent]

There should not be "land and groove marks" on ANY case no matter what caliber or chamber. This goes for any rifle, not just an AR.

[andrew]

Ooops, pardon my dumbness. They are just weird (to me) crimp marks, not one continuous circular crimp, but a series of 6 crimps with a tiny space in between each making me think that they were imprints of the lands and grooves.

The same marks are on the unfired rounds too, but the soot on the fired cases highlighted the pattern, making it stand out more. I guess I don't look at enough ammo.

[karcent]

Those are just a different crimp style that is used on a lot of foreign manufactured NATO ammo.
If you were able to fire that ammo thru your AR with no extraction problems and every thing else looks ok, then you probably havea 5.56 or Wylde chamber.
You should be fine.

[andrew]

Those are just a different crimp style that is used on a lot of foreign manufactured NATO ammo.
If you were able to fire that ammo thru your AR with no extraction problems and every thing else looks ok, then you probably havea 5.56 or Wylde chamber.
You should be fine.

Thanks for that input. I was actually kind of worried about running this ammo thru my rifle, as I had some issues with South African commercial packaged ammo labeled as Remington .223 with case heads stamped .223, manufactured by PMP. Primers were flattened and several times the extractor ripped a chunk of the rim off without extracting the cartridge. I assumed that the ammo was mis-labeled 5.56 and that my chamber was actually .223.

Anyway, the M855 worked just fine again today.