Chamber question

[moondog]

First off, I'm NOT a gunsmith. I'm trying to understand and make sense of what was told to me recently. I sent 2 Barrels in to get chambered recently. One is a 4 groove, one a 6. Both cut rifle. The 4 groove looks good the 6 groove, not so much. Lots of tool marks and the lands are not concentric or even. Not sure I'm describing this right.I've only looked at a couple dozen chambers, but this one looks bad to me. Smith said it could be caused by the lands being different depths? I'm sending it back, but if that's the case, maybe I should bail on it. Anyhow, could that be the case? It might be the best shooting barrel I've ever owned. Maybe this means nothing. Thoughts before I pull it?

 

[ShtrRdy]

Several years ago I had a gunsmith chamber a barrel blank in 308 Win. When I got it back and looked at it , it looked like the reamer was off center and that the guide bushing had made a bunch of scratches. This really surprised me because this 'smith had always done outstanding work for me. When I brought it back for him to look at, one of the things he did was remove the 90° mirror from the bore scope and have a look. This presented a more reasonable picture. The scratches now looked like scuff marks and the leade part of the chamber looked better. He asked if I would be willing to try it first and I did. That barrel turned out to be fine and has worked well.

 

[Judd]

What shape are you seeing? When I first started chambering, I did a 6.5 saum…I looked and it was U shaped. I thought I did something wrong…mentioned it to my mentor and he said the lands weren’t the same height across them. When I think of a good shooting barrel, that one still pops in my head…it was/ is a hammer!

The bigger question is, how does it shoot?

 

[FireMedic]

How the groove is shaped can cause a cut to look uneven. Sometimes one side of the groove is cut deeper then the other. I can tell what a finished throat will look like when indicating the barrel before I make the first cut.

Button rifled barrels can be dished in the middle of the land and in the groove. This can make some weird looking patterns in the throat.

I much prefer a high quality cut rifled 4 or 6 groove barrel. They most always look perfect when chambered correctly.

 

[LVLAaron]

On top of what others have said... is it consistent around the entire 360 degrees? Meaning; is the throat bigger on one side than the other?

 

[Alex Wheeler]

Would need to see pics

 

[tobnpr]

Is this what you're seeing? This is one of mine- groove diameter of the barrel is slightly larger than the reamer. I'm sure not ideal- but this particular barrel still shot just fine. What's more important is that they're even and concentric.

 

[moondog]

Wish mine looked like that. No, they are not even and concentric. I only have a Hawkeye, so pictures through it are impossible, I just tried. I know the tooling marks will go away with enough rounds down it. The uneven lands bug me. At this point, I think I'm just going to shoot it and see. I'm chalking it up to an expensive lesson. I've got more sand in the bottom of the hour glass then above. Just trying to get a few more years shooting in. Thanks for the replies

 

[ShtrRdy]

Wish mine looked like that. No, they are not even and concentric. I only have a Hawkeye, so pictures through it are impossible, I just tried. I know the tooling marks will go away with enough rounds down it. The uneven lands bug me. At this point, I think I'm just going to shoot it and see. I'm chalking it up to an expensive lesson. I've got more sand in the bottom of the hour glass then above. Just trying to get a few more years shooting in. Thanks for the replies

Try it out with some known factory match ammo, if possible. (you may have a barrel that needs hand load only) I think you'll know pretty quickly if there's a problem.

 

[moondog]

Try it out with some known factory match ammo, if possible. (you may have a barrel that needs hand load only) I think you'll know pretty quickly if there's a problem.

Haven't shot a factory load in 18 years.

 

[Alex Wheeler]

Is this what you're seeing? This is one of mine- groove diameter of the barrel is slightly larger than the reamer. I'm sure not ideal- but this particular barrel still shot just fine. What's more important is that they're even and concentric.

View attachment 1640381

Is that a 5 groove

 

[moondog]

6 groove left twist that matters

 

[ridgeway]

Button barrel? It's the shape of the land causing what you are seeing.

Like this....

 

[moondog]

Button barrel? It's the shape of the land causing what you are seeing.

Like this....

Cut rifle.

 

[jackieschmidt]

If the lands and grooves were not the same depth, (rare in a cut rifled barrel), that Gunsmith should have noticed that when setting the barrel up.

It is difficult to say why some things come out the way they do. More times than not, you simply have to rely on the skill and attention to detail that is employed by the person performing the work.

One problem that can arise, and bugs me to no end. Is when a particular spot of “runout” occurs exactly where the throat of the chamber is established. This can happen more often when you are having to cut quite a bit of the chamber ends length off in order for the final barrel to make weight.

This could be what happened with the 6 Groove.

 

[moondog]

Thanks Jackie. I've been breaking it in some, so I'm going to see how it shoots this week.
I guess that's where I'm at now. Just tell me it's a bad barrel and it's not cutting correctly, I could live with that.