Carbon on necks tied to bolt lugs

[Bob Wright]

I am reading on a bench rest Facebook page where a distinct pattern on the necks is evidence of locking lugs either in high contact or not. Ever paid attention to this phenomenon before?

 

[Mikecr]

Any mention of how or why?

 

[Bob Wright]

Any mention of how or why?

Nope. Just the comments saying " oh yeah, bolt lugs, perfectly normal". Still scratching my head.

 

[Bob Wright]

Some of the 13 comments:

 

[Bob Wright]

The FB o.p. mentioned Tony Boyer ( multiple x world champ in BR) and his book. Not sure if this is covered there.

 

[Phil Rizzo]

So, the carbon stain and shape? is related to lug contact.

 

[Bob Wright]

So, the carbon stain and shape? is related to lug contact.

That's what the commenters are saying. I want to know how they figured that out. Mine never had that but I'm not shooting benchrest chambers either. Stumped.

 

[tonyf3]

I can offer nothing other than this picture. I recall hearing this on a pod cast not long ago when i was driving.
might have been Jack Neary who said something about it.

 

[Phil Rizzo]

Neck is too thick is the same as not enough clearance when fired I’m assuming?

 

[tonyf3]

I found the podcast. kids were asleep so i was half listening to it. Clearance is what they seem to be referring to. So i guess thickness of neck is in relation to the chamber size.


this link put you right about the 13min mark

 

[MagnumManiac]

Is it April first again…

Cheers.

 

[Bob Wright]

So apparently my neck turning is good with adequate clearance. Carry on!

 

[MagnumManiac]

So apparently my neck turning is good with adequate clearance. Carry on!

So is mine, but I often get a ‘wave’ of carbon on my necks and all of my actions are trued and blueprinted. My 22-250AI barrel was chambered slightly eccentric and it carbons one side only, never thought anything of it until now…

Cheers.

 

[BrentM]

I’ve always found it to be a sign of brass thickness or annealing. Any time I see a lot of carbon on the neck I assume the chamber is not sealing correctly and to me that is a first indication of improper annealing or hard brass.

What they seem to be saying is the lug is allowing the case to be offset in the chamber? Trying to get my little bird brain wrapped around that concept. So much is happening during the ignition and expansion of the brass in the chamber in nano seconds.