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true freebore

 
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  #1  
Old 03-06-2014, 10:06 PM
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Join Date: Mar 2011
Posts: 48
true freebore

I've searched quite a bit on various forums and get a variety of definitions. None of which I can accurately relate. So, here is my question.
Based on SAAMI 30-06 the measurement from base to the end of the case is 2.502". Measurement to the taper to inside neck diameter is 2.5228" (.0208" difference). the measurement to the beginning of the lands is 2.7442". This results in a distance of .2422" from the front of the actual case to the beginning of the bore.
Assuming that the lands begin at the exact point of the beginning of the bore (2.7442") is the "freebore" then .2422"?

I guess what I'm asking is if the "freebore" is the distance from the front of the case to the beginning of the lands?

As a case in point, my Remington 700 30-06 has a base to lands distance of 2.846". Using the SAAMI distance (case length) of 2.494" base to end of case, my freebore would be 0.352". Ammunition loaded to placate my Marlin XL7 (with 165 grain Nosler Partitions at 3.26" COAL & 0.036" jump) would have a "bullet jump" of .240".
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  #2  
Old 03-06-2014, 10:17 PM
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Join Date: May 2013
Location: Elkhorn Idaho
Posts: 305
Re: true freebore

You pretty much have the concept. Remember on the oversized mags they have to have freebore to avoid pressure spikes and cross bridging with certain powders. The best cartridges built (Weatherbys) have upwards of .37 to .40 freebore. The ultra mags especially the 7mm rum has generous amounts of freebore. Most of the time freebore rifles usually like harder bullets like the Barnes. You can get them to shoot if the bolt is trued. The chamber is tight, especially in the neck and the barrel is aligned perfectly. OR YOUR REALLY LUCKY.
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  #3  
Old 03-06-2014, 10:28 PM
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Join Date: Nov 2011
Location: The high desert of wyoming
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Re: true freebore

Quote:
Originally Posted by ballistx View Post
I've searched quite a bit on various forums and get a variety of definitions. None of which I can accurately relate. So, here is my question.
Based on SAAMI 30-06 the measurement from base to the end of the case is 2.502". Measurement to the taper to inside neck diameter is 2.5228" (.0208" difference). the measurement to the beginning of the lands is 2.7442". This results in a distance of .2422" from the front of the actual case to the beginning of the bore.
Assuming that the lands begin at the exact point of the beginning of the bore (2.7442") is the "freebore" then .2422"?

I guess what I'm asking is if the "freebore" is the distance from the front of the case to the beginning of the lands?

As a case in point, my Remington 700 30-06 has a base to lands distance of 2.846". Using the SAAMI distance (case length) of 2.494" base to end of case, my freebore would be 0.352". Ammunition loaded to placate my Marlin XL7 (with 165 grain Nosler Partitions at 3.26" COAL & 0.036" jump) would have a "bullet jump" of .240".

Maybe I am Not reading or under standing you right, but it seems you are mixing head space and freebore mesurements togather. My understanding of freebore is the distance of the ogive to the lands and has nothing to do with case length. Case length, base to shoulder has more to do with head space.
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  #4  
Old 03-06-2014, 10:41 PM
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Join Date: Mar 2011
Posts: 48
Re: true freebore

That is the confusion. If it is the ogive, then there is no absolute freebore measurement for any rifle. It is relative to the cartridge/bullet combination. So, the term "the rifle has ".xxxx" freebore is meaningless.

However, headspace should be limited to the case and should be independent of the bullet relationship to the bore/lands. Headspace should be limited to the body segment of the chamber, not the barrel segment.
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  #5  
Old 03-07-2014, 04:16 AM
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Join Date: Aug 2003
Location: NC, oceanfront
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Re: true freebore

Quote:
Originally Posted by wyomingblizzard View Post
My understanding of freebore is the distance of the ogive to the lands
No, this is JUMP(roughly).
Freebore is set by the chamber reamer, but there are several common ways to consider it:
-Chamber neck end to land begin
-Chamber end to land begin(lead)
-Same references but to ogive contact(as set by ogive radius/type & leade angle)

The value that matters to me is seated distance to land contact -per bullet.
Predicting this up front for filling out a reamer print, etc, is not very easy. Best done with a program, and reamer makers can do it for you.
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  #6  
Old 03-07-2014, 11:26 AM
Edd Edd is offline
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Join Date: Jan 2011
Location: Tulsa
Posts: 1,007
Re: true freebore

One thing that may be confusing you is, you are looking at a 30-06. It doesn't have any freebore. The throat starts at the neck/bore transition angle. Look at the modified 30-06 reamer print at this link. It has a .086" freebore. You still have to consider the total distance from the base of the case to the lands when seating bullets.


Rem 40XL: .30-06 Long Action
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  #7  
Old 03-07-2014, 12:09 PM
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Join Date: Mar 2011
Posts: 48
Re: true freebore

For that reamer, I would calculate the "freebore" to be 2.603" - 2.517" or 0.086".
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