Case head marks from AR bolt

[Hummer70]

The striker indents appear to be wanting to reverse flow. Normally the M16 requires a very hard striker indent to reliable ignition which comes with deeper fired primer indents. If the hammer spring is not up to spec the pressure rises, allowing the striker to head in the other direction. I had this bad on my 7615 and checked the striker energy and it was too low. I replaced the hammer spring with new Wolf spring and the indents now look correct.

This is normally tested by measuring the depth on a pressure copper in a copper holder that looks similar to a headspace gage. The SAAMI standard for 223 now is .016" indent depth and was .020". The M16 spec calls for .022" indent. The hardest primer to ignite in US inventory is Cal 50 followed by primers for 5.56MM.

 

[mehavey]

Appears to me that brass has two opposing burnish marks on the outside rim. Neither looks like
ejector cutout. The primers look "unremarkable" (as doctors say)

Instead, the burnish marks appear consistent with a possible uneven bolt face that scrapes the case (which has
stretched back to meet it on firing) upon opening rotation.

- Are you able to confirm that the bolt face is totally flat?
- (Since you build ARs) do you have another bolt that would give you acceptable headspace to try out?

 

[thesheepdog]

Okay guys I did a little test.

Using 5.56 NATO ball ammo and my handloads loaded to NATO pressures, and using different guns, the marks still show up, both guns.

I even turned down the gas on both guns and that didn't change anything.

I think the ammo is just hot but not dangerous.

 

[Cavitation]

The first pic looked like crappy handloads the second pic looked fine to me.

 

[AR15barrels]

3 of those cases look like they have pull marks.
If so, that is a sign of too much gas.

Read this:
www.ar15barrels.com/prod/operation.shtml

Then look at the cases from the other side and see if there are pull marks on the rims.

Also, how many firings are those cases?