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Barrel leads up too much

I clean the barrel and the next 8-10 shot are quite accurate, then pattern gets spread out, pushing a slug thru then measure shows .1775-.1780 . I'm thinking the ammo is not being spun by the rifling and being shaved causing too much lead left behind, does this make since ? I've already replaced the barrel and unfortunately it is same size as original beeman barrel. Oversized bore with almost no choke. Have not found any pellets or slugs with larger dia to try.
 
You didn't mention what rifle or who the barrel manufacturer is. My FX barrel liners have tight chokes and foul rather quickly. After pushing a slug through, they measure 0.173-0.174. In your case, maybe you are pushing the velocity too fast? Just guessing.
I'm kinda ashamed to admit but it's a 180$ beeman single shot. I have many pcp rifles but never had one that leads up in ten shots, I've polished the barrel and checked both ends of barrel for imperfections, after running patch it shoots 1/2 inch pattern for 8 to10 shots then goes to 3 inches all at once , run a patch back tight again. Doesn't matter what brand of pellet. Tried speeds from 600-950fps.
 
Jan 21, 2018
3,047
1,011
MS, United States
    I'm thinking the ammo is not being spun by the rifling and being shaved causing too much lead left behind
    Are the patches coming out with lots of shiny flakes or even thin slivers?

    pushing a slug thru then measure shows .1775-.1780
    Bear in mind slugging the barrel will yield a measurement of the groove diameter. The land diameter is somewhat smaller, and the lands are what matter for pellets...they support the head to keep the pellet running true, while the blast of air puffs out the skirt to conform to the bore and seal fully.

    Can you share a close-up photo of a couple different pellets after being pushed through the barrel? Preferably with pellets whose heads measure 0.177 - 0.178. I'm curious how much engraving will be shown at the perimeter of the heads.

    For example, even the slight amount of engraving shown on the left is more than adequate:

    engraving2.jpg


    It would also be helpful to see if the rifling is producing nasty striations:
    pellet striations.jpg
     
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    Are the patches coming out with lots of shiny flakes or even thin slivers?


    Bear in mind slugging the barrel will yield a measurement of the groove diameter. The land diameter is somewhat smaller, and the lands are what matter for pellets...they support the head to keep the pellet running true, while the blast of air puffs out the skirt to conform to the bore and seal fully.

    Can you share a close-up photo of a couple different pellets after being pushed through the barrel? Preferably with pellets whose heads measure 0.177 - 0.178. I'm curious how much engraving will be shown at the perimeter of the heads.

    For example, even the slight amount of engraving shown on the left is more than adequate:

    View attachment 301379

    It would also be helpful to see if the rifling is producing nasty striations:
    View attachment 301380
    Hope these pics work its best i can do, they were all pushed thru barrel
     
    Jan 21, 2018
    3,047
    1,011
    MS, United States
      Okay yeah the pictures of the two slugs (0.177 and .1772) show no engraving whatsoever. Not even burnishing marks from light contact, at least not that I can make out in the photos. So that suggests the lands are somewhere over 0.177.
      rawroots pellets.jpg

      Turning to the larger Norma pellet (0.178), I can't make out sufficient detail at the rim of the head to see burnishing but I think engraving would be showing up in the photo if there were any and I'm not seeing it. So yes I think that confirms the bore is oversized.

      For now I will assume the lands are at something very close to 0.178. Meanwhile the oversized slug emerges at 0.181:
      rawroots slug.jpg

      The numbers mean the engraving can be no deeper than 1.5 thousandths. It looks deeper than that but it could just be my perception. At the very least, I think it means the lands can't be 0.179 or larger. 0.178 is probably the number.

      For the few shots it groups well after a cleaning, which of the pellets listed will group? Other than the Norma, everything else would be unsupported by the rifling and would therefore likely scattershot all over the place. A possible exception may be a pellet whose skirt is thin enough to obturate and sufficiently center it in the bore.
       
      Okay yeah the pictures of the two slugs (0.177 and .1772) show no engraving whatsoever. Not even burnishing marks from light contact, at least not that I can make out in the photos. So that suggests the lands are somewhere over 0.177.
      View attachment 301445
      Turning to the larger Norma pellet (0.178), I can't make out sufficient detail at the rim of the head to see burnishing but I think engraving would be showing up in the photo if there were any and I'm not seeing it. So yes I think that confirms the bore is oversized.

      For now I will assume the lands are at something very close to 0.178. Meanwhile the oversized slug emerges at 0.181:
      View attachment 301446
      The numbers mean the engraving can be no deeper than 1.5 thousandths. It looks deeper than that but it could just be my perception. At the very least, I think it means the lands can't be 0.179 or larger. 0.178 is probably the number.

      For the few shots it groups well after a cleaning, which of the pellets listed will group? Other than the Norma, everything else would be unsupported by the rifling and would therefore likely scattershot all over the place. A possible exception may be a pellet whose skirt is thin enough to obturate and sufficiently center it in the bore.
      You are 100% right figuring my mess here, the norma are the ones flying well after clean, I'm thinking that beeman sent me a replacement barrel from a returned rifle because the barrel sealing o-rings looked like they were gouged from transfer hole. Appreciate your time spent here, thank you