Gunsmith Help
 

A friend of mine owns a semi-custom Weatherby Mark V .340 Wby. Mag.; the rifle was a factory Mark V .300 Wby. Mag. which grouped under 3/4" at 100m.

The semi-custom Mark V .340 Wby. Mag. has a HS Precision Stock which has allunium block bedding, and has been glass beded. The barrel is a SS Shilen #4 contour. A muzzle brake was directly machined on to the fluted barrel; it is not removable. It has a Timminy Trigger. The rifle is shoots patterns not groups using handloads, or Weatherby (Norma) ammo. Its not the shooter because three of us have received the same results.

Please give me your thoughts of why this semi-custom rifle is shooting patterns not groups. Thanks

We can only guess, but if the work was done by someone that knows what they are doing, I suspect the scope and/or scope mounts.

This^^^^

Something is loose or the scope is bad. I was on an elk hunt and stopped in to zero at elevation before the hunt. After a box of rounds, I was on my way to the small town to pay way to much for a scope but it fixed the problem. Scopes do go bad, especially if it is a cheaper brand of scope on a heavy recoiling rifle.

Nothing is wrong with the scope or mounting system.

Do you folks have any other ideas. Thanks for your help

This might be something you've already tried, but was there at least 3-4 types of different ammo tried to see if the rifle preferred some types compared to others?

I take it you have already tried another scope? That's the only way to know it's not the scope.

If you have decent ammo, everything is tight and it's not the scope, it's time to take it back to the smith that did the work.

Is the new barrel free floating?

6mm-06:

We have shot Weatherby Factory, and handloads.

Colorado Lucky Dog:

We installed a NIB Burris 3-9x40 Full Field II. The Gunsmith may be dead.

Vapo Dog:

Haven't heard form you for a while. When the HS Precision stock was instaled it was free floated.

Thank you and try th keep the solutions comming.

Time to find a new gunsmith. Something is out of spec.

To start it's a Mk-V magnum action. Sorry to say but that action design with the 9 locking lugs doesn't lend itself to great accuracy. To find a factory rifle that regularly shoots .75moa is the exception rather than the rule.

#2. A #4 Shilen is a pencil thin barrel for a .338 magnum the size of the .340 Weatherby. It's pretty whippy.

#3. Get a chamber cast done that includes the full length of the throat and measure the casting against SAAMI maximum and minimum specs for the .340wby. Also measure the length of the throat. Weatherby ammo is designed so that the bullet needs a bigger jump start before the cartridge reaches peak pressure to maintain acceptable chamber pressure levels. If you have a very short throat you could be reaching to much pressure with factory loads which may cause inaccuracies. The throat may also be a little on the loose side causing the bullet to engage the rifling inconsistently from one shot to the next.

#4. Make sure that the bullet is not striking the muzzle brake. I don't think I need to explain this one.

#5. The crown may have been machined slightly off or it could have a ding or burr. Remove the brake and check the crown. Unless he soldered it or pinned it to the barrel it is removable.

#6. This barrel could simply be a dud. It happens. Have a gunsmith look at it with a bore scope and inspect the rifling.