Throat burned out or not???

I have a used 7MM Weatherby mag in a Mark 5 action that will not hold any kind of a group less than about 3". It was made in Japan in Jan. 1994, 26" SS #2 contour. I seat a 175gr Speer GS just into a new case which gives me a total COAL of 3.781. I place in chamber and close the bolt, after removal the total COAL is 3.767. Which leaves only 14 thousands of bullet in case when the bullet hits rifling. That gives me a free bore of about .402. The Speer GS has a lot of bearing surface, any other bullet will leave the case before it hits the rifling, really not good! Am I missing something important here or is the throat gone? What is good free bore on replacement barrel?
I got this weapon for long range Mule Deer and Elk so I want the extra velocity. Now, long range for me is about 500 yds. my eyes and reflex isn't what they were many years ago.
Thanks for any information on this post.
AIRBORNE

I just did a work up with the same rifle. tried a lot of combinations to get 1 moa out of it. Check the twist- the one I worked on was a 10 and it wouldnt shoot any bullets over 160 grains

Sounds like it's toast... Also sounds like a typical Weatherby with excessive freebore. I am not a fan of massive freebore, it makes chasing the lands difficult.

If I were you, I'd rebarrel to a 1:8 twist 26" 7mm RemMag. Cheaper, brass and ammo is everywhere, and it does the same exact thing as the Wby. Also, no excessive freebore to fight with trying to chase the lands, like with the Wby cartridges.

The twist rate is most likely the accuracy issue. Try lighter bullets recommended for 10twist barrels.
Personally I'd rebarrel with an 8twist barrel and leave it 7mm wby. Heavy 7mm bullet should be able to eat up some of the freebore.

If you really want to get past the long Throat on a Weatherby cartridge you'll need to define your own reamer and have it made. Then have a barrel chambered with that new reamer.

May I add chasing freebore has a lot to do with bullet also. Berger are very sensitive and benifit from jump tests.
Wby's All have lots of freebore. Try the new hammer bullets they seem to not be jump sensitive at all. May be just what you need to shrink groups. If you do a new barrel don't worry about jump. They can shoot well.
I believe JE customs on here does quite a few roy's May be worth a chat with him.

Sent JE Custom a text, will see what he has to say.
AIRBORNE

Before you give up, try a jump test. I'd start with bearing surface .280" deep in your case and go deeper by .010" increments until your bearing surface is in the shoulder.

It might not improve much, but you'll know for sure if it's toast. The test is cheaper than a new barrel. I'll bet a long jump will shoot better than what you're getting now.

I did a jump test, sort of, I loaded 139gr bullets and my groups opened to about 6". Or are you talking about something else?
AIRBORNE

I'm speaking of a seating depth test, sorry if I confused you. Try different seating depths, starting with roughly a caliber's diameter (.284") of the bearing surface in the case neck. Seat at least 3 at that cbto, then 3 @ .010" deeper, then 3 @ .020" deeper and so on, until the bearing surface/ ogive junction is very near the case neck. One of those seating depths should show much better groups. You need a bullet comparator to measure CBTO accurately with calipers. CBTO is the measurement from base of the case to an equal diameter on the bullet ogive. This way, the bullet is jumping an equal distance to the lands.

The freebore your reporting is in line with what the sammi print here is the 7rm and the 7wby. Notice the different angles of the leade as well as the lengths. Do a seating depth test using the 139's seat them with the boatail/baring surface at the neck shoulder then seat 10 bullets @.005 deeper for each bullet. Once you have them bring your chrony to the range and shoot the 10. Keep the barrel cool and note your velocities and impacts. Shoot this as far as your comfortable. If nothing cluster up start at the deepest and do another 5 bullets @ .010 The 7mm weatherby and the 154 hornady was the original favorite. I'd start with that bullet and maybe a 150 barnes and gameking. The 10tw won't be too friendly with the heavier class of bullets that are not round nose style
https://screenshots.firefox.com/g2ob5uD2VF8maO3y/saami.org
https://screenshots.firefox.com/IkEyzZ6cTphgKh1d/saami.org

Ok I understand the seating depth test and have on hand the 154 by Hornady and the Sierra Gamekings, Nosler and Rem Cor-Loc. The 154 H and the Nosler and Cor-Loc are flat base bullets only the Sierra is BT. So what you are suggesting is to seat the base of the 154 even with the base of the case neck, then each of the next 10 bullets are to be seated a +.005 deeper into the case, right????

dok7mm
It is not difficult to corn-fuse me. What you are saying is that my concern over the .402 free bore is most likely not the problem but is incorrect seating depth is most likely the problem. I will do a seating depth test and check my Chrony along with holes on paper to see if it helps.