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Freebore question

 
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  #1  
Old 02-18-2012, 09:41 PM
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Join Date: Jan 2010
Location: NC mountains
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Freebore question

I'll make this as brief as possible.

The barrel on my Savage (McGowan) got loose and I took it to a friend's house this week to re-headspace it and tighten the barrel properly. We used all the right equipment and he is very knowledgeable in this area. Bolt closed with the go gage, and didn't with the no go. So we tightened the locking nut down and off I go.

I decide to measure my distance to the lands tonight with my Hornady LNL tool, as I suspected that if the barrel had been working it's way loose with successive firings, then the distance to the lands would be INCREASING. Right?

I looked at my notes and found that my distance to the lands in November was 2.720". When I measured this distance again this evening if found that the distance is now 2.913"

I used the same tools in my measuring process. The only variable that was not exact was the bullet that I used was not THE bullet that I used to measure back in November. Both measurements were with the same bullet (Berger 168gr).

Help me wrap my head around how this is possible. It seems very counter-intuitive for me. If I assume that the barrel was properly headspaced before, and it is properly headspaced now, then how is there that much difference in the distance to the lands? If the distance would have been a few thou of an inch, then I could have chalked it up to different lots of bullets, my measuring, Jupiter's position in the solar system, something. But a difference of .193" seems HUGE to me.
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  #2  
Old 02-18-2012, 11:08 PM
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Join Date: Dec 2008
Location: Northern Id.
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Re: Freebore question

Quote:
Originally Posted by CRNA View Post
I'll make this as brief as possible.

The barrel on my Savage (McGowan) got loose and I took it to a friend's house this week to re-headspace it and tighten the barrel properly. We used all the right equipment and he is very knowledgeable in this area. Bolt closed with the go gage, and didn't with the no go. So we tightened the locking nut down and off I go.

I decide to measure my distance to the lands tonight with my Hornady LNL tool, as I suspected that if the barrel had been working it's way loose with successive firings, then the distance to the lands would be INCREASING. Right?

I looked at my notes and found that my distance to the lands in November was 2.720". When I measured this distance again this evening if found that the distance is now 2.913"

I used the same tools in my measuring process. The only variable that was not exact was the bullet that I used was not THE bullet that I used to measure back in November. Both measurements were with the same bullet (Berger 168gr).

Help me wrap my head around how this is possible. It seems very counter-intuitive for me. If I assume that the barrel was properly headspaced before, and it is properly headspaced now, then how is there that much difference in the distance to the lands? If the distance would have been a few thou of an inch, then I could have chalked it up to different lots of bullets, my measuring, Jupiter's position in the solar system, something. But a difference of .193" seems HUGE to me.
That IS huge! I can think of three reasons for this: One or both of your measurements was off (probably not likely) You have fired it so much that it has eroded to this point (again probably not likely) The bullets have that much variation (I would hope not) although I have seen quite a bit of variation in some of the Bergers I've had. It might be a combination of all three?.........Rich
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  #3  
Old 02-19-2012, 05:54 AM
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Join Date: Jan 2007
Location: PA
Posts: 1,079
Re: Freebore question

Nearly two tenths of an inch difference is huge. But if your properly headspaced now, start over with OAL measurements; forget about before. Different bullets and even different lots of the same bullets can vary in their lengths.

A bullet comparator of any kind should get you close to the lands, but not necessarily spot on. Take 4 or 5 measurements and average them, write it down and seat the bullets based on that distance.
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  #4  
Old 02-19-2012, 10:05 AM
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Join Date: Jan 2010
Location: NC mountains
Posts: 508
Re: Freebore question

Quote:
Originally Posted by elkaholic View Post
That IS huge! I can think of three reasons for this: One or both of your measurements was off (probably not likely) You have fired it so much that it has eroded to this point (again probably not likely) The bullets have that much variation (I would hope not) although I have seen quite a bit of variation in some of the Bergers I've had. It might be a combination of all three?.........Rich
I am certainly able to screw up. There's no doubt about that. I just don't think I screwed up that much. The rifle was probably only fired at most 50 times between measurements, so I know I didn't blow that much of the throat out. I tend to lean toward your thinking that it was a culmination of two of the factors (my measurements and bullet variation).

One more thing that came to mind: I wonder if back in November when I took the readings I had a dirty bore? I usually clean the rifle after every firing session, but I guess there is the possibility that there was some gunk in there. Still seems like a far stretch to me.
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  #5  
Old 02-19-2012, 10:12 AM
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Join Date: Jan 2010
Location: NC mountains
Posts: 508
Re: Freebore question

BREAKING NEWS: I AM A DUMBASS!!!!!


I found that my measurements get MUCH better when I use the comparator made for my 7mm and not my .243!!!!!
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  #6  
Old 02-19-2012, 10:15 AM
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Join Date: Sep 2011
Posts: 130
Re: Freebore question

HA! Glad you got it figured out.

Dont think your the only one who has done something like this....
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  #7  
Old 02-19-2012, 10:16 AM
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Location: Lynchburg, TN
Posts: 735
Re: Freebore question

You didn't say. What caliber are you shooting? There are some real barrel burners out there.
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