distance to the lands ?

[rebs]

Before I got a bore scope my measurements to the lands with SMK bullets were
80 gr 1.923
77 gr 1.945
69 gr 1.966
After when I got the borescope and completely cleaned out the carbon my measurements are
80 gr 1.955
77 gr 1.971
69 gr 1.80
Is it possible for the distance to the lands to change that much from just shooting the rifle? Could it be possible that the bullet was hitting the carbon ring before I cleaned it out and giving me a false measurement such as I was actually measuring to the carbon ring and not to the lands ?

 

[CJ6]

Yes and Yes.

 

[rebs]

Yes and Yes.

Thank you for the reply

 

[rwj]

Were any rounds were fired between the times when the distances were measured? How repeatable are multiple measurements?

 

[fkimble@charter.net]

Might want to check that 69 again. The other two numbers got bigger, the 69 got smaller.

Frank

 

[mfendley]

Might want to check that 69 again. The other two numbers got bigger, the 69 got smaller.

Frank

I think he missed a digit. I bet he meant to type 1.980, although that would be a bigger difference than the other two.

 

[SKWERLZ]

I think he missed a digit. I bet he meant to type 1.980, although that would be a bigger difference than the other two.

That could makes sense, the 69SMK has a tighter radius for the ogive so a more acute angle at contact point?

 

[D-4297]

To ease your mind about this whole issue . Many aren't used to measuring things by the thousandths of a inch . That's normal for anyone not in the machine trades . Take you calipers and close them to zero . Then carefully open them to .032 . That ; from your description , is the width of your former carbon ring . Look thru the gap in between the caliper blades . Not really all that much , but enough to mess things up . That's why you see a lot of discussion about carbon rings , and why you shouldn't let them find a home .

 

[D Coots]

Big carbon ring if a bullet hits it. The carbon ring didn't exist until Tony Boyer invented it in his book....

 

[Doom]

Have to ask are the bullets the same ones you used on the original measurements? If not then you really don't know what the difference is.

 

[rebs]

Have to ask are the bullets the same ones you used on the original measurements? If not then you really don't know what the difference is.

yes same brand and weight

 

[Longtrain]

yes same brand and weight

You need to use the same physical bullets to make a comparison, especially when using Sierras. The LTO on Sierras can vary significantly bullet to bullet. This will skew your results.

 

[rebs]

You need to use the same physical bullets to make a comparison, especially when using Sierras. The LTO on Sierras can vary significantly bullet to bullet. This will skew your results.

Thank you for the information

 

[rebs]

Big carbon ring if a bullet hits it. The carbon ring didn't exist until Tony Boyer invented it in his book....

So does the carbon ring need to be removed or not?

 

[Propbndr]

Eric Cortina is an F class shooter who has 2 excellent videos on “chasing the lands”.

You may want to watch them on how he addresses it. He has many videos on the shooting subject.

 

[Longtrain]

So does the carbon ring need to be removed or not?

Yup, scrub that puppy out. Use a worn brush with a patch rolled on to it, add a smear of JB Bore Paste, Iosso or ThorroClean and give it 25 short strokes in that area, run it down the full length a few times, clean it the residue, borescope, repeat as needed.

 

[rebs]

thank you

 

[Mulligan]

Yup, scrub that puppy out. Use a worn brush with a patch rolled on to it, add a smear of JB Bore Paste, Iosso or ThorroClean and give it 25 short strokes in that area, run it down the full length a few times, clean it the residue, borescope, repeat as needed.

Good advice

When I hear or read "carbon ring" I think of the carbon that forms just in front of the mouth of the case.
So I am not really sure if the discussion is about a carbon ring or carbon buildup in the throat area, either way the above advice is solid.

CW

 

[chop house]

You need to use the same physical bullets to make a comparison, especially when using Sierras. The LTO on Sierras can vary significantly bullet to bullet. This will skew your results.

exactly. i call it them the 'golden bullet' but really they are just a coupon to use in the measuring process. labeled, stored separate, and treated with care.

 

[D Coots]

So does the carbon ring need to be removed or not?

Yes, but it doesn't need to be Squeaky clean. Just don't let it build up.