7mm freebore

trueblue

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Joined
Feb 18, 2008
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Location
IOWA
What freebore is needed for the 168gr and 180gr Bergers in a reamer in order to put the BT of the 180 Berger at the neck/shoulder junction, and what does that do to the 168 BT location. Looking at buying a 7 STW reamer. And is there a compromise between the 168 and 180's for freebore that will work for both ?
 

trueblue

Well-Known Member
Joined
Feb 18, 2008
Messages
2,312
Location
IOWA
I know what the COAL will be based on a reamer print and the length of the Bergers from the top of the BT to the end.
Just trying to figure out how to determine what freebore I need to make both work.

168gr Berger oal= 1.445
- .220 for BT
---------
1.225 + 2.582( boltface to neck/shoulder of 7 STW)= 3.807 COAL w/ 168gr Bergers seated w BT @ neck/ shoulder = 3.807

180gr Berger oal=1.525
- .220 for BT
________
1.305+ 2.582(boltface to neck/shoulder of 7 STW)= 3.887

So if I comprimise the COAL of 3.840-3.850 it should be fine for both bullets.
Just don't know how to determine the freebore for this setup. The 168's should still be seated deep enough in the neck, and the 180's should not be seated to deep. What freebore are you guys using on your 7 STW reamers and what is the COAL of the Bergers seated on the lands ?
 

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