Gunsmithing 30-30 keyhole

[Osmosis]

I am getting towards the end of what I know to do to solve the problem.
It's an old marlin that is tumbling bullets about as soon as they leave the muzzle.

The barrel is in good shape, says the gunsmith.
one of the first steps in trying to fix the problem was a recrown. I just got the bolt back from plating, the headspace was a little out so I had them plate the face to bring it back.
Still having the problems.

Pre crown: tumbling bullets horrendous pattern
post crown: no change

pre bolt plating: same as pre/post crown
Post plating: every bullet still tumbling, but 5" at 50yds so it solved atleast one problem.

of course tried multiple bullet designs and weights, so that's not the issue either.

What would you do next?
I suppose a new barrel is my only option now

 

[MAGUA]

Re: 30-30 keyhole

What is the barrel twist ? and weight of the bullet you are using ? The wrong combo will always cause tumbling/keyholing.

 

[JMC]

Re: 30-30 keyhole

See if you can some how measure the bore. I would think that it would have to be either too long of bullets or an over-sized bore. It almost sounds like you might have a 32 Special barrel to get that much inaccuracy.

 

[former naval person]

Re: 30-30 keyhole

I agree with JMC. Slug the barrel and find out the dimensions.

 

[Osmosis]

Re: 30-30 keyhole

I tried from 125 grain up to 170 grain and none of 'em changed the problem. I even loaded up some with bullets I run out of my .308 to see if I got away from the tube mag type flat nose bullets it would change anything.

The barrel's stamped 30-30 win, but I will dowel some lead through it and find out.
Thanks

 

[buffybuster]

Re: 30-30 keyhole

Slug the bore. I presume you're shooting lead (not jacketed) bullets.