Marlin 30/30 Help

[charlie4570]

      Just wanted to say I have been buying your molds for a year or two now and nothing else compares. I shot some .433" 320 gr WFN from my Stainless Ruger Super Redhawk (lapped with about 220 shots). Four shots touching for 1" center to center @ 100yards with last two opening up two 2" c.t.c. but I think that was me not gun as the 2x scope blots out the bulls-eye and my eyes aren't the best any more. I have never shot groups like these before and am tickled to death. Back when I used the bullets from Cast performance or Bear tooth 3" to 4" was the best I could do. I thought it was me, but I kept reading where you said an accurate pistol is the best teacher and boy that is true. I now have confidence that if the gun isn't performing that it is not me. I thought for years I was not a good pistol shot even though I am a good rifle shot, but thanks to you pistol shooting is now rewarding for me. I was very scared of lapping a barrel but now am lapping all my guns.
     I am now having a problem with a marlin 30/30. I lapped it about 80 shots and got under 1" 4 shot groups at 100 yards with 1600 fps but opened up to two inches after more shooting. 2000 fps was 2" groups after cleaning and 2400 fps was about 5" groups. There was some lead streaks so I lapped 20 more shots. I don't see lead streaks now but still will not maintain 1600 fps accuracy and 2400 fps is no better. I tried water dropped bullets next but no different. Should I lap more or do something else. the bullet was your 170 grain LCFN air cooled and aged 2 weeks, sized to .312 and lapped with your compound. There is no constriction in bore anymore and is fairly smooth pushing slug thru but not glass smooth like my ruger.

[Veral]

  Thank you for making this post.

  It is REALLY difficult to over lap a barrel using my lap kit and pushthrough slugs to monitor progress.
  The push through slugs are the key to prevent overlapping, or under lapping.  When they slide through smooth as silk from breech to muzzle the bore is precision within less than 1/100,000 of an inch.  It would take a lot of sorting and luck to find a match grade barrel that precise.

  When there is some jerky motion on the push through, it could be as little bore variation as the above 1/100,000, and it could be as much as .001 or .002 if the change is smooth, which makes the tiny measuring band on the push through crush down with little effort.