The 110 Matchkings are LONG. When i was shooting them i didn't worry as much about the base of the bullet going past the end of the neck, i worried more about getting them to feed out of a AICS mag. Unless you're single feeding the gun, I'm not sure you'll get exactly what youre after. So, lets look at this. Its a quite simple math problem.. at least i think.
We will use some figures off the print I have attached to this post. Its my 6 Creed Reamer JGS is making me right now.
*My Bearing surface is calculated with only one bullet, so your numbers may vary some. I also have only one Hornady 6mm comparator. Getting another one and measuring bearing surface with two would be much more accurate. *
-OAL of chamber: 1.915
-Base to beginning of Rifilings: 1.9313 *This number will change your freebore.*
-Case Base To Neck/Shoulder Junction: 1.6484
-Bearing surface of 110 SMK: .510
So,
Base to Beginning of Rifilings-Case Bast to Neck/Shouilder Junction=
1.9313-1.6484= 0.2829
Bearing surface-0.2829= ~ Freebore
.510-.2829= .2271
So, freebore would be .2271. Sound about right?
I'm unable to see your print, which may help me with some observations I have.
Your bearing surface seems awful long. I measured several bullets with a Davidson comparator. You don't need two comparators, you can just zero your caliper with the comparator installed. Then take a bullet oal (base to meplat)off the face of the comparator. Record the number and zero the caliper on that figure. Now take a traditional measurement from base to ogive. The resulting negative number is your nose length. Now flip the bullet and take a meplat to bearing surface measurement(boat tail /bearing surface junction). That negative number is your boat tail length. Now subtract nose and boat tail from bullet oal, and you have bearing surface. I think you'll find the bearing surface is much shorter than .510. I use a Davidson comparator, which has no chamfer and the hole size is .239"-.240". These figures will cause variations between different comparators of course. Just for a general comparison, Berger lists the bearing surface length of a .30 cal 230gr Hybrid at .529".
Here's the bearing surface numbers I came up with for three bullets:
Berger 105 .382
Sierra 110 .381
DTAC 115 RBT .420
If you use any of these new bearing surface measurements with your other numbers, the freebore range is .1371" for the DTAC, and .098 for the 110 smk. Now those seem short, but that's because your math puts bearing surface at the neck shoulder junction(shorter OAL than it needs to be). I seated a 110 into a lapua creedmoor case to a depth of .220", and the base to meplat OAL was 2.820, short of an AICS mag. That seating depth puts my bullet bearing surface .050 above the neck shoulder junction. If we add .050" to the numbers above, our new freebore is .1871 for the DTAC (.1371+.050), and .148 for the 110 (.098 + .050). You can see though how the freebore numbers we know(saami 6CM freebore is .183) are right in line with the numbers I have above. There are a number of errors we can make during measuring that would change these numbers up slightly. If we have some wiggle room to seat shallower or deeper, while still fitting in the magazine, those errors are just noise.
One other thing to note with your chamber length. When I formed Hornady and Lapua brass to 6MM, the resulting case lengths were 1.920 for the hornady, and 1.917 for the lapua. In other words, you'll need to trim before you can load with new brass. If it were me, I'd make the chamber length longer, like 1.925 or so.
