Help me diagnose symptoms with my AT

[jfields]

Sometime in the last 150 rounds or so my rifle has:

1.) Started piercing primers
2.) Accuracy went from .3" @ 100 yards to over an inch
3.) Extractor will not pick up unfired rounds or empty brass.
4.) Started flattening primers on a load that previously demonstrated no pressure signs

It ejects fired cases fine.
load is 115 DTAC over 41.4g H4350 CCI200
Rifle has about 4,000 rounds on it.
Barrel has 310.

Anybody got any ideas?

 

[Jedi]

Does the fired brass have a pronounced ejector wipe?
Sounds like pressure ring issue due to carbon build up etc

 

[jfields]

No Ejector swipe. Carbon rings have pestered me in the past, so that was the first thing I addressed. Borescope showed no carbon ring after cleaning. I did re-measure distance to the lands and discovered that I was a little long. I seated the bullets about 20 thousandths deeper and saw no change after cleaning and adjusting seating depth.

 

[jaycoux]

Did you say 4000 rounds on a 6mm?

 

[jfields]

Did you say 4000 rounds on a 6mm?

On the rifle. A little over 300 on this barrel.

 

[Kevin1]

Your barrel has increased in speed and is showing pressure signs. This is pretty common. Do another load dev with lighter charges.

 

[jfields]

Your barrel has increased in speed and is showing pressure signs. This is pretty common. Do another load dev with lighter charges.

I loaded up another OCW Test with lighter charges last night. Do you think the not ejecting loaded rounds or unfired brass is a separate issue?

 

[Kevin1]

The increase in the pressure of the previous load might have modified the geometry of the extractor.

 

[jfields]

The increase in the pressure of the previous load might have modified the geometry of the extractor.

I can see something like this happening.

 

[308pirate]

The increase in the pressure of the previous load might have modified the geometry of the extractor.

What exactly do you mean by that? How can the extractor "geometry" change without deformation of the extractor itself? And if the extractor is now deformed, I'd say it's time to replace it because it has been taken beyond its yield point.

 

[JePhyllis]

I think it might be the bolt issue due to your description. Did you disassemble the bolt recently? Is it locking tight when chambered?

 

[mi223]

If it is not ejecting unfired rounds if could be the brass is stretched somewhere it shouldn't if it has seen excessive presure.

Heve you tried with new brass?

Sent from my SM-G930P using Tapatalk

 

[trophyhunter]

It was the extractor

 

[jfields]

It was the extractor

I'll have it out this weekend to see how things go. Thanks for everyone's comments.

 

[RyanM]

I think a little while back there was another thread on here where a guy had an out of spec extractor on his AI. It seems odd that it would start failing all of a sudden though.

Why don't you throw the 308 barrel back on and see if it works with that?

What kind of speeds are you getting out of that load? You don't mention the cartridge so I assume 6 Creedmoor?

 

[redneckbmxer24]

Your barrel has increased in speed and is showing pressure signs. This is pretty common. Do another load dev with lighter charges.

This for 1, 2, and 4.

As far as 3, I would say it's unrelated to the pressure events. Is your extractor pushed rearward?

 

[jfields]

This for 1, 2, and 4.

As far as 3, I would say it's unrelated to the pressure events. Is your extractor pushed rearward?

I also think we had an excessive headspace issue. The shoulder on the barrel has been set back 7 thousandths. Previously the bolt would close on a no-go gauge, now it will not.

 

[MattyG]

Sounds like headspace to me......

I have seen countless flattened primers and cases not being picked up by the extractor because someone pushed the shoulders back too far.....

With a shortened headspace the primer actually pops out of the case and rests against the bolt face, then the case case expands and swages back over the primer cup giving a flattened appearance. This is not due to pressure, rather it is a mechanical effect.