Scarring Across the Chamber Throat a Problem?

[Pdvdh]

Looking for some feedback? Please take a look at these photos I took of the throat in a cut rifled barrel I just had chambered. The neck of the chamber is visible to the left, and the rifling visible at the right side in these two photos. So the pics are centered on the throat.

The score marks run the length of the throat longitudinally, extending from the groove back to the neck of the chamber. So even after the chamber reamer cut the throat, these score lines were deep enough to remain present across the throat. The scars are just showing off the end of one of the 6 grooves

I don't know if these score marks were left by the cutter when the grooves were cut into the bore, or from lapping. I'd guess from the cutter. Guessing the cutter cut this one groove deeper than the other 5 grooves.

I don't see these score marks in the throats on any other barrels in my collection. Would you contact the barrel manufacturer if this were your barrel? Or shoot it and throw the dang bore scope away? I know bore scopes reveal the minutia, but like I said, I've not seen this before. Anybody else seen this scoring after cutting the chamber/throat? Thanks...

 

[Muddyboots]

Tagging in

 

[tobnpr]

Or shoot it and throw the dang bore scope away?

The grooving aside (had to be from the rifling process far as I can tell) is the leade otherwise cut perfectly concentric to the bore? The edges of the where the rifling begins again should all be perfectly aligned with clean edges all the way 'round.

They could be real copper grabber, but maybe not so bad...

I'd contact the mfg, let them know and send them the pics to document it.
Then I'd shoot it. You just never know- I've seen (and own) some butt-ugly barrels that shoot great.
Bird in the hand, ya know... If it doesn't shoot you've only "lost" a few dozen rounds of ammo to find out.

 

[Pdvdh]

The leade looks concentric. Doesn't appear to be a case of the throat cut off-center. At least not to my eye.

I'm thinking it would be pretty difficult to cut a throat off-center, since the roller nose shaft on the chamber reamer is so close, immediately adjacent to, the leade and the throat.

 

[dflyfish]

Any chance this is a button cut barrel?

 

[Pdvdh]

Not a chance. This grooves in this barrel were 100% cut.

 

[dflyfish]

I'm curious to hear the cause. The grooves / tooling marks / scratches seem way to uniform. To be clear are they in the direction of the breach to muzzle? If that's tru they probably couldn't come from chambering as they would most likely be 90 deg from muzzle to breach. It's almost as if there were a pile of chips and a gage for round was forced in.

Please post the outcome!

 

[Pdvdh]

Yes, these score marks run uninterrupted from the adjacent groove on out across the throat. They likely run the full length of this groove. The score marks are so deep that they remain visible in the throat, after the throat was cut by the chamber reamer. In this 338 bore, the throat should be very close to .3385" diameter.

I believe if the bore diameter were measured from this deepened groove to the opposing groove, the bore would be larger that 0.338". Likely around 0.33825".

But I have no way to obtain this measurement.

 

[Bob Wright]

I would notify barrel maker. Those look like drag-out marks from the rifling cutter ( possibly chips caught). The only way to tell if it is, does the same pattern extend forward into the barrel past the lead taper. Even if it's lapped, there should be a pattern similar extending forward.

 

[Pdvdh]

Yes, the score marks extend forward into the adjacent groove. If you can enlarge the first photo, you should be able to follow the scoring right on into the adjacent groove.

Thinking the cutter ran down this groove one or more times too many. That or there were some protrusions on the cutter which cut these score lines excessively deep.

Kinda bummed, at the moment. Time for a bottle of beer...

 

[dflyfish]

If it was chip build up galling it would wrap around the entire chamber/ bore.

If this wasn't a barrel I would say someone used band old school corn cob rougher and forgot to add some comp.

 

[Bob Wright]

Yes, the score marks extend forward into the adjacent groove. If you can enlarge the first photo, you should be able to follow the scoring right on into the adjacent groove.

Thinking the cutter ran down this groove one or more times too many. That or there were some protrusions on the cutter which cut these score lines excessively deep.

Kinda bummed, at the moment. Time for a bottle of beer...

It probably occurred in the final pass, final groove, since it's at finished groove dia. Could be a worn or failed cutter, to chips packing up. That's machining for ya.....it happens.

 

[cabelasken]

I had a similar problem with a 257 roberts barrel installed on a Mauser action. The gunsmith left tooling or cutter marks on the chamber walls deep enough that as the cases were fired a couple of times the bolt became difficult to lift. I spent hours honing the chamber walls with a light buffing compound in an attempt to take off the high spots and even now some cases will stick. unfortunately the problem was discovered after the gunsmith had moved to another city. The score marks on my rifle's chamber walls are similar to the pics above.

 

[Muddyboots]

Or lack of coolant?