How Aligned Should the Lands / Throat Be in 556 Barrel

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Dave1911

New member
Silly me decided to look down a new 416R barrel with a boroscope before I shot it. And now I am questioning if I should fire it.

It's a 223 Wylde chamber. There are six lands that are offset from each other. Going around the loop there is about a 1/4" offset. It appears something may have been cut at an angle. Does this seem extreme? What is an acceptable offset?

If I have the terms correct, the start of the lead varies by 1/4" going around the circumference. And there is essentially no throat or freebore for land #1 but a 1/4" freebore for land #6.

Any thoughts are appreciated. Thanks
 
1/4" is quite a lot around the circumfrince of a .224 barrel.

What looks like 1/4" on the screen may only be 0.030".
Don't forget a borescope magnifies.
 
Of course,it should be perfectly concentric. (Which may not always happen)

In theory,the fit of the reamer pilot to bore diameter will limit the condition you describe. Before I give you more information than you asked for, IMO, what you describe is not a barrel I would accept. I doubt its dangerous, but I doubt it has accuracy potential and it may be a metal fouler.
Talk with your barrel supplier diplomatically. I'm not a lawyer, but I suspect you can't MAKE your barrel supplier do anything. HOW you communicate can makea difference. A picture is worth a thousand words. Sending the documentation/pix to the barrel supplier avoids a lot of needless BS.

I'd guess that would get you a return authorization.

Now, stuff you don't necessarily need to know. Some "value" barrels are made in China...Hard saying what you get.

Top quality USA barrel blanks CAN be screwed up as you describe by the person who cuts the chamber.

The reamer pilot must be the slightest smaller than bore diameter. A few tenths of a thousandth, Just enough to not bind. Then the reamer pretty much has to align with the bore. There are solid pilot reamers and interchangeable pilot reamers, A solid pilot reamer must fit the tightest bore
to be chambered. But you may get an AR Stoner blank or a Lilja or a Wilson or a Kreiger or a Shaw or a Green Mountain or a Shilen... The bore diameters vary. So the clearance around the pilot varies. A pilot undersize from bore diameter will allow the condition you see. Interchangeable pilot reamers are available to address this problem.

Good luck.
 
1/4" is quite a lot around the circumfrince of a .224 barrel.

What looks like 1/4" on the screen may only be 0.030".
Don't forget a borescope magnifies.
Click to expand...

Edit: I was using diameter instead of circumference to estimate the land separation. This put me off by a factor of pi or 3.14".

It is my friend's borescope. I think the 0.25" number I originally stated may be a little high but in the ballpark. The two concerns where the lack of a freebore for one land and "angled" freebore going around the circumference. He has significant experience scoping competition barrels, and he said I might consider calling the manufacturer based on what the scope showed. He also cautioned firing. The next day I asked him how much offset he thought we saw on the screen and he said maybe 0.25". That number may not be too far off.

I am going back to get an actual picture. But I would estimate the 1/4" to be closer to 0.175". We had a 3" x 2" horizontal screen. The two "extreme" lands were close to the diagonal corners of the screen. The 2" vertical of the screen showed the land radial separation which should be on the order of 223*3.14 / 6 = 117 plus the curvature distortion minus the width of the land. Call it 0.117". And the horizontal showed the land start offset going from one side to the other of the screen. 3/2 x 0.117" = 0.175".

Thanks for the replies and if I get a hard copy I will post.
 
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Of course,it should be perfectly concentric. (Which may not always happen)

In theory,the fit of the reamer pilot to bore diameter will limit the condition you describe. Before I give you more information than you asked for, IMO, what you describe is not a barrel I would accept. I doubt its dangerous, but I doubt it has accuracy potential and it may be a metal fouler.
Talk with your barrel supplier diplomatically. I'm not a lawyer, but I suspect you can't MAKE your barrel supplier do anything. HOW you communicate can makea difference. A picture is worth a thousand words. Sending the documentation/pix to the barrel supplier avoids a lot of needless BS.

I'd guess that would get you a return authorization.

Now, stuff you don't necessarily need to know. Some "value" barrels are made in China...Hard saying what you get.

Top quality USA barrel blanks CAN be screwed up as you describe by the person who cuts the chamber.

The reamer pilot must be the slightest smaller than bore diameter. A few tenths of a thousandth, Just enough to not bind. Then the reamer pretty much has to align with the bore. There are solid pilot reamers and interchangeable pilot reamers, A solid pilot reamer must fit the tightest bore
to be chambered. But you may get an AR Stoner blank or a Lilja or a Wilson or a Kreiger or a Shaw or a Green Mountain or a Shilen... The bore diameters vary. So the clearance around the pilot varies. A pilot undersize from bore diameter will allow the condition you see. Interchangeable pilot reamers are available to address this problem.

Good luck.
Click to expand...

Great information. Makes sense. The more I learn the less I know

This is an American made barrel from a popular manufacturer. I am going to hold off on saying much more until I have a picture and can talk with the manufacturer.
 
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