300 Weatherby Magnum in a Winchester Mod 70

[47WillysGuy]

A friends Winchester Mod 70 chambered in 300 Weatherby Magnum has a 5" group at 100 yards. The brass shown is factory fired brass and 30 cal bullets can not even begin to inserted into the case.
Case length fired - 2.820
Case headspace - 2.391
Case neck thickness - 0.0137
Case Neck Fired Dia- 0.338

I'm at a loss for a solution.

 

[Murray Brook]

It would seem the neck clearance is on the tight side. Was there any pressure signs with the factory loads.

 

[47WillysGuy]

None at all.

 

[Murray Brook]

Weird. Normally when you can't slip a bullet into a fired case it is because the chamber neck clearance is too small and you would see pressure on even medium loads. If you have the tools to turn one case to .012 and fire it , may give you an idea as to the neck clearance you have. I guess a chamber cast would be ideal.

 

[47WillysGuy]

Saami chamber drawing shows a taper of 0.001” on the neck section of the reamer drawing. 0.430 shoulder to neck area and 0.339 at the transition to the leade area. That’s tight when the neck diameter averaged 0.338”.

These dims are correct, if I can read the Saami drawing correctly.

A gunsmith told about 50% these guns are accurate, the other 50 not so much!

A challenge, I guess.