Assuming you have a barrel with a short-ish throat, and use a Uni-Throater to extend the throat to match a given dummy round... how would you go about determining (after the fact) approximately what the new freebore dimension is?
Gunsmithing Determining freebore after throating?
- Thread starter memilanuk
- Start date
Did you take a measurement pre-reaming of the BTO touching the lands? You could use that as a reference to establish the amount of additional freebore.
Or if you have lots of experience with the given cartridge, you could use that prior knowledge of average BTO as a reference point then measure the new BTO.
Simple
Set a bullet in a case long and incrementally seat bullet deeper till you can feel it ride on the shoulder and not the bullet and take measurement.
Do the same after.
Throat needs to be clean and use the same case and bullet.
Every barrel I get I do this with the primary bullets I intend to use in it.
Set a bullet in a case long and incrementally seat bullet deeper till you can feel it ride on the shoulder and not the bullet and take measurement.
Do the same after.
Throat needs to be clean and use the same case and bullet.
Every barrel I get I do this with the primary bullets I intend to use in it.
One method I have used in the past is to mount my digital bore scope in a toolpost holder. Run the bore scope into the chamber end of the barrel while the barrel is on the lathe. Find the start of the throat and use a reference mark on the screen to align with the start of the throat. Set your DRO to zero then run the bore scope in deeper until you align the end of the throat with the reference mark on the screen. Read your DRO and that is your throat length.
Possibly fabricate a stopper for the body of the uni throater and use calipers for measuring small cuts at a time. My method for determining distance to rifle lands is a good one that I have come up with years of reloading the steps are as follows.
1. Using new brass or resized brass apply dry graphite based lube (redding dry lube with ceramic applicator beads) to the inside of the neck.
2. Seat bullet so that it completely expands the neck of the cartridge from top to bottom.
3. Use a kinetic bullet puller and completely remove seated bullet.
4. Reapply dry lube
5. Insert bullet into this cartridge.
6. This cartridge will have just enough neck tension to soft seat the bullet.
7. Insert round into chamber and close bolt.
8. Extract round and measure using bullet comparator.
9. Use steel wool and lightly polish the copper jacket to remove shiny spots that reveal lands of barrel. (verify you are in the lands)
10. Repeat this process 3 times and if they all measure within a couple thousandths, you have found your throat distance.
11. Generally I have fount that this method leaves the bullet 10-15 thousandths into the lands.
12. You can verify exact distance by using bullet seater and steel wool seating the bullet after cleaning a couple thousandths at a time till the shiny spots disappear from the copper jacket.
Hope this helps, I use this method every time I open a new box of bullets to verify seating depth. I usually load rounds 10-15 thousandths into the lands due to the fact that I shoot vld style bullets mostly.
1. Using new brass or resized brass apply dry graphite based lube (redding dry lube with ceramic applicator beads) to the inside of the neck.
2. Seat bullet so that it completely expands the neck of the cartridge from top to bottom.
3. Use a kinetic bullet puller and completely remove seated bullet.
4. Reapply dry lube
5. Insert bullet into this cartridge.
6. This cartridge will have just enough neck tension to soft seat the bullet.
7. Insert round into chamber and close bolt.
8. Extract round and measure using bullet comparator.
9. Use steel wool and lightly polish the copper jacket to remove shiny spots that reveal lands of barrel. (verify you are in the lands)
10. Repeat this process 3 times and if they all measure within a couple thousandths, you have found your throat distance.
11. Generally I have fount that this method leaves the bullet 10-15 thousandths into the lands.
12. You can verify exact distance by using bullet seater and steel wool seating the bullet after cleaning a couple thousandths at a time till the shiny spots disappear from the copper jacket.
Hope this helps, I use this method every time I open a new box of bullets to verify seating depth. I usually load rounds 10-15 thousandths into the lands due to the fact that I shoot vld style bullets mostly.
