Marlin 336 30-30 keyholeing?

[Warden Callaway]

Son has plenty of experience with guns. He came across an old Marlin 336 Sporter "waffle top" at local shop and bought it. It had seen a couple of alterations.  One was the muzzle shortened about 1/4" and funky flat crown.   He shot it for the first time yesterday at 25 yards and both shots keyholed.   Using Federal 170 factory loads. We talked back and forth about it. While the crown looks funky, it should do much better that that. I had him insert a .308 bullet in the muzzle,  thinking it may be relined to a 32 Special.  But no, it's a 30 caliber.  Brass looks fine.  I'm 700 miles from the gun but he's bringing it down in deer season. Maybe work on the crown. Got nothing to loose. Any ideas? 

 

[Texas Joker]

Is the barrel bulged? 

 

Is the crown cut square? 

 

[Dirty Dan Dawkins]

My bet is the rifling is worn out. Is this an early microgroove?

I don't see any rifling in that muzzle. 

336 30-30 Keyholing | Marlin Firearms Forum (marlinowners.com)

 

Time for ya'll to cringe, 

I cut 4" off of a savage 110 a few years back with a hacksaw. Squared it with a file and square, then recrowned by hand with a case mouth chamfer tool. It shot sub-moa before and after.

[Cyrus Cassidy #45437]

I'm going with the crown.  A gunsmith can re-crown that.

[Subdeacon Joe]

Slug the barrel and mic the bullets.

 

When I had an H&R .38-55 I bought hard cast lead bullets according to the published literature.  Keyhole.  Slugged it and it was 0.0035 over the published data.  That meant the bullets were undersized.

 

Also, examine that crown with a magnifier, there might be a small flaw in it.

[Dirty Dan Dawkins]

I blame it on Communism.

[Forty Rod SASS 3935]

1 hour ago, Dirty Dan Dawkins said:

I blame it on Communism.

It's Trumps fault.  Ask your left wing politicians.  

[Pat Riot]

Years ago a friend bought a 336 because he loved mine. He had the same issue. Lovely sideways profiles of his bullets in the target. 
He was quite upset. I let him try some of the factory loads I brought. Same thing. 
It turns out the prior owner shot a bunch of lead bullets through the micro-groove barrel. 
It took my buddy a while but he got the lead out (no pun intended) and it shot like a champ. 
Perhaps the barrel is leaded up. 

[The Original Lumpy Gritz]

Ck bore for leading with a bore scope.

Slug the bore.

Recut the crown.

 

[Rye Miles #13621]

2 hours ago, Pat Riot said:

Years ago a friend bought a 336 because he loved mine. He had the same issue. Lovely sideways profiles of his bullets in the target. 
He was quite upset. I let him try some of the factory loads I brought. Same thing. 
It turns out the prior owner shot a bunch of lead bullets through the micro-groove barrel. 
It took my buddy a while but he got the lead out (no pun intended) and it shot like a champ. 
Perhaps the barrel is leaded up. 

Similar to what happened to a  friend of mine. He bought it from somebody who  was doing a lot of cowboy long range. Once he got the lead out the rifle shot fine!