Breech face marks

[Keith Glasscock]

I have the barrel off of my Barnard 3 lug action. This rifle is shot in F-open and gets hot.

I see these marks which are an exact match for the bolt head and lugs in the closed position.

Do these marks indicate a lack of adequate bolt nose to breech cone clearance?

The rifle shoots well, but does throw a few unexpected vertical shots as it warms or cools.

Edit: Spelling

 

[Ggmac]

Go to your auto parts store , ask for plasti- gauge , used to check engine bearings , stick a small piece on the front of bolt and close the action , keeping it cocked , then open bolt and compare to plasti-gauge wrapper .
It could be that your bolt nose touches when not cocked and empty chamber .

 

[Keith Glasscock]

If it helps, I just did a rough check with scotch tape. With 2 thicknesses (about .004) placed on the bolt nose and the barrel hand-tight in the action, the bolt would not close. With 1 thickness, it did close, so my guess right now is that I have ~.003" clearance with a cold rifle.

 

[ab_bentley]

I have the barrel off of my Barnard 3 lug action. This rifle is shot in F-open and gets hot.

I see these marks which are an exact match for the bolt head and lugs in the closed position.

Do these marks indicate a lack of adequate bolt nose to breech cone clearance?

The rifle shoots well, but does throw a few unexpected vertical shots as it warms or cools. View attachment 988708

Looks like residue, not necessarily scaring. I bet you have .005" or less clearance. Allowing dirt and other junk to stain the metal.

Jmo, Adam

 

[JohnKielly]

My recollection is that Barnard recommends .005" bolt cone clearance.

 

[Matt P]

Do You dry fire much ???
I have seen marks like these even with enough clearance, it's normally caused by dry firing with out a snap cap.
I use 0.008" clearance on all the barrels I fit and with the Barnard design this still give 100% case support.
Matt P

 

[Alex Wheeler]

Non issue. There will be at least .010" between the bolt handle and the extraction cam/rear or the action. There will be .005"-.0010" from the bolt to the breech. That means the bolt will contact the breech at times. However those times will not be when its important for accuracy ie. during lockup and firing.

 

[Dans40X]

OP,
breech dimensions are too tight.