Gunsmithing Barrel chambering- counter-bore

[SmartDonkey]

I'd be very surprised if this hasn't been covered- I didn't find it searching, but probably am using the wrong terms-

Just getting into working with the lathe and am going to chamber a few practice barrels before I go at my expensive one. I was told by a guy that he just skips the "counter-bore" when working on a 700 and does it like a Savage. He claims that it doesn't cause any issue. With just a little thinking on it I came up with a few possible issues- (other than safety in a case failure). There would be less threads engaging the action- and it would probably make single feeding more difficult.

In any case I want to do it the right way- but it did get me thinking. When you guys do a Savage or a Bighorn with a shouldered barrel do you counter-bore them or is there something preventing this from being the case. Maybe not enough threads on the action or with the savage the locking lugs may be to large to give enough room. My Origin prefit looks like it would have room for it- but wasn't done. What say you?

 

[cattleman99]

Savage or Bighorn actions have a flat bolt face so they don’t need a counter bore. A Remington bolt needs a counter bore as it’s part of the “three rings of steel”. The Remington bolt face is not flat like that of a Savage or bighorn

 

[SmartDonkey]

I understand the "three rings of steel" and that a Savage bolt is designed differently than the remington (oddly- the very old savages had a very similar bolt to the Remington and had a counter bore.) What I was asking, apparently poorly, is if it is possible to counter bore the barrel for the whole bolt face? As stated it wouldn't work on a Savage because the locking lugs take up almost all of the material. But on something like a Arc Nucleus or even a Ruger American it looks like you could counter-bore for the locking lugs- and then you would have more barrel screwed into the action and also another "step" in the barrel to potentially help with single feeding. On the Ruger American in particular it is very difficult to single feed because it just runs into the back of the barrel- my maybe flawed idea- was if you could recess for the lugs and give a "ramp" to guide the cartridge in.

 

[Steel head]

I understand the "three rings of steel" and that a Savage bolt is designed differently than the remington (oddly- the very old savages had a very similar bolt to the Remington and had a counter bore.) What I was asking, apparently poorly, is if it is possible to counter bore the barrel for the whole bolt face? As stated it wouldn't work on a Savage because the locking lugs take up almost all of the material. But on something like a Arc Nucleus or even a Ruger American it looks like you could counter-bore for the locking lugs- and then you would have more barrel screwed into the action and also another "step" in the barrel to potentially help with single feeding. On the Ruger American in particular it is very difficult to single feed because it just runs into the back of the barrel- my maybe flawed idea- was if you could recess for the lugs and give a "ramp" to guide the cartridge in.

The Nuke takes flat breech just like a savage.
it single feeds just fine, I single feed my 7 saum often and have to single feed my 338 edge.

You gain more strength and rigidity by having a bigger diameter tenon over having a longer tenon.
No real advantage I see complicating something If not needed.

 

[Ledzep]

In the unlikely event that a case ruptures, you are going to have less probability of shit in your face with the counterbore there (M700 standard design).

That being said, for normal operation, it effectively does nothing. The extra thread or two are not going to meaningfully make the joint stronger (especially at <150 ft-lb installation) or more rigid or more aligned or whatever theoretical gain you think might be there. The counterbore does not affect case exposure.

To answer your question, so long as you have sufficient clearance to add whatever feature, then yes you can counterbore anything or put a conical breach face or whatever. But again, an extra thread or two isn't going to add anything functional, and an extra step or cone isn't going to aid in feeding except in what I'd call "rare" geometric circumstances. It'd end up being an extra step for the sake of having an extra step IMO.

ETA: I think to have a meaningful ramp close enough to the chamber to help with feeding is going to require removal of material on the bolt nose and/or will expose more case head when chambered.

 

[Easy_E]

If your doing lots of Remingtons just get the counterbore cutter it does a nice job cutting and chances of going too deep or wide.

 

[LRI]

"Three rings of steel" can just as easily be called "three rings of bullshit" because all it is/was is 1960's marketing crap.

There's nothing any stronger about it. If anything it puts the bolt head at a slight disadvantage on a magnum because the wall thickness of the nose portion is so thin and being that Remmy countersinks the face around .155" it begs to be "bloomed" like a flower in the event that you sneeze a case. At least with "flush face" bolts, the lugs fatten things up on the sides.

It might affect feeding a little, but from a strength perspective your not giving anything away by "flat breeching" an M700 barrel. It's been done by many smiths for decades.

For those of us who hang onto the countersunk breech face, the biggest thing in today's world is getting the diameter opened up enough so that if an M16 extractor goes in later down the road, (magnum stuff especially) the barrel doesn't have to come back off to have the ring enlarged.

 

[Steel head]

"Three rings of steel" can just as easily be called "three rings of bullshit" because all it is/was is 1960's marketing crap.

I understand it’s to bleed off speed from gasses but I’ve seen cases sneeze on a Remington and savage and honestly didn’t see any difference.

 

[Edds]

In any case I want to do it the right way- but it did get me thinking. When you guys do a Savage or a Bighorn with a shouldered barrel do you counter-bore them or is there something preventing this from being the case. Maybe not enough threads on the action or with the savage the locking lugs may be to large to give enough room. My Origin prefit looks like it would have room for it- but wasn't done. What say you?

It isn't going to work. The minor diameter of a 1-1/16" thread in slightly smaller than 1.0". The counterbore diameter is going to need to be about 1.0" in diameter for a flat faced bolt.