Throat concentricity

[DaveTooley]

Arguably the most important factor in chambering. I just finished up some 308 accuracy barrels for a customer and took a look at them. I use a 2 1/2X jewelers loupe for inspections. Just for the hell of it I tried my phone. A little fuzzy but it worked. Attached is the throat of one of the barrels. It is very easy to see the line at the end of the freebore in relation to the groove. This is a SAAMI chamber and the FB measures .310". In a chamber that's .0005" over the line gets thinner but is still easy to see if you have a concentricity problem. These were done with a bushing that was at least .0005" under bore diameter. Using a loupe I can also see the surface finish on the leade.

 

[BuffaloBill]

Nice pictures Dave.

 

[WSnyder]

And it appears that it's a "5R" profile barrel to boot and no concentricity errors??? Say it isn't so

 

[tobnpr]

I'm puzzled...
Why do those pictures show no taper on the rifling leade? I'm looking at squared-off edges.

I use a borescope so I'm looking at it from 90 degrees, but I don't understand the lack of any taper?

 

[Dusty Stevens]

Youre the man dave

 

[DaveTooley]

I'm puzzled...
Why do those pictures show no taper on the rifling leade? I'm looking at squared-off edges.

I use a borescope so I'm looking at it from 90 degrees, but I don't understand the lack of any taper?

The angle is there. Because of the resolution of the pic all you see is the shadow. The shadow magnifies the height of the land. If it was clear you'd see the angle and the surface finish.

 

[LVLAaron]

310 free bore or did I misread that?

 

[DaveTooley]

Yep SAAMI is .310"

 

[Jerry Wick]

Just to be contrary, I had a 6PPC barrel several years ago and that freebore ring that you see was so far off center I thought it would never shoot. I don't think I could duplicate it if I tried. I've no idea how I did it.

I decided to shoot it before rechambering and darned if it wasn't one of the best barrels I've ever had. Very insensitive to conditions and I never had to change my load throughout the day. I'd call it a hummer despite the off-center chamber.

 

[LVLAaron]

Dr Tooley - can you recommend a particular type/brand of loupe??

 

[DaveTooley]

I've got a busted up B&L 2 1/2X I hold together with electrical tape that I've used for close to 30 years. You don't want more power. Increased power shortens the focal length. 2 1/2X covers everything up to magnum length. 3 1/2X is great for short action cartridges.

Individual Loupe for Jewelry and Watchmaker Standard Plastic 2.5x to 10x

A jewelers loupe makes internal flaws and surface blemishes more apparent and allows you to assess color, cut, and other aspects of a stone. Also great for watchmakers and repairing jewelry. Brings what you need to view up close.

www.esslinger.com

Bergeon 2611-TN Jewelers Eye Loupe Magnifier with Opening

Innovative new eye loupe by Bergeon are available in 5 magnifications and two colors. They feature plastic bodies, sight opening and removable lenses. Excellent choice for any jeweler or watchmaker. Swiss made.

www.esslinger.com

 

[DaveTooley]

IMPORTANT
For any of you that get these loupes please don't freak out and start calling the barrel maker. Over time you will see many abnormalities in land configuration that DO NOT show up on the target.

 

[LVLAaron]

I bet you thought of that before you were falling asleep last night. “Oh hell, I’m gonna piss off a lot of barrel makers”

 

[Carl S]

Nowt wrong with that Dave,great picture.

 

[Jesswil61]

I've got a busted up B&L 2 1/2X I hold together with electrical tape that I've used for close to 30 years. You don't want more power. Increased power shortens the focal length. 2 1/2X covers everything up to magnum length. 3 1/2X is great for short action cartridges.

Individual Loupe for Jewelry and Watchmaker Standard Plastic 2.5x to 10x

A jewelers loupe makes internal flaws and surface blemishes more apparent and allows you to assess color, cut, and other aspects of a stone. Also great for watchmakers and repairing jewelry. Brings what you need to view up close.

www.esslinger.com

Bergeon 2611-TN Jewelers Eye Loupe Magnifier with Opening

Innovative new eye loupe by Bergeon are available in 5 magnifications and two colors. They feature plastic bodies, sight opening and removable lenses. Excellent choice for any jeweler or watchmaker. Swiss made.

www.esslinger.com

Dave,
Can you please provide the brand of electrical tape you are using!

 

[DaveTooley]

Dave,
Can you please provide the brand of electrical tape you are using!

I left out that a rubber band is holding the electrical tape in place.

 

[okie]

perfect.

 

[rjtfroggy]

Come on I don't think a new one will break the bank.

Amazon.com : jewlers loop

 

[Riesel]

I left out that a rubber band is holding the electrical tape in place.

Need pics or it ain't so

 

[Dusty Stevens]

Heres mine.