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Thread: Concave or Flat crown

  1. #1

    Concave or Flat crown

    Why do some rifles have a concave crown and others have a flat one? - - - and as an afterthought - - would a convex one be inherently less accurate ?

    JR
    " not the end of the world, - - but you can see it from here ! "

  2. #2
    Convex would be very suceptible to damage.

    Concave every time. Steve Kershaw does a beautiful concave crown.
    Brian.

    Just because you are paranoid, doesn't mean they aren't out to get you......

  3. #3
    flat crowns tend to be on factory screwcut rifles in my experience.
    the expectation that they will either have a thread protector or a moderator protecting the crown and lands

    not sure concave is the correct term though as that would indicate a curve inwards
    a more common profile is an 11deg flat slope into the bore

    "convex" is quite common on older rifles but you will find the convex profile is from the outer diameter to the inner bore presenting a raised profile to protect the bore and lands

  4. #4

  5. #5
    Thanks for that - - interesting stuff.

    JR
    " not the end of the world, - - but you can see it from here ! "

  6. #6
    I never understood the part of raming in a 60deg counter sinker into a freshly crowned barrel.
    Most counter sinkers fitted into a normal 3 jaw chuck like a power tool. Totally out of centre.
    A centering guide at 500-1000 revs will do it's bit too inside the bore.

    If one has already set the bore to centre why not turn the 60deg chamfer...if one really wants one.
    I once turned a 15 deg no chamfer crown which worked a treat.
    edi

  7. #7
    The standard sporting crown was like this:-



    On most rifles. Of course it's turned whilst the barrel is being finished.

    The target rifles often had no crown as such as target shooters were expected and believed to be able to care for their rifles better than the normal type of shooter........................... well they sure got that idea wrong .



    The chamfer to the bore is I believe a later addition and not done by BSA at the factory on this .22 Model 12/15.

    Then I believe they adopted the recessed crown in which the barrel as not crown really but the muzzle is recess to protect it. Thought I had a photo or two of the recessed crowns by Parker-Hale on the 1200V and 1200TX but it seems that I don't.

    The 11 degree crown became popular with target shooters a few decades back but somehow there seems to be no hard and proven facts that the shape of the crown matters. It's vitally important that the crown is true to the bore though.

  8. #8
    The shape and angle of a crown has no bearing whatsover on a rifles potential accuracy.
    The most important factor is that the crown is perpendicular to the bore, so that as expanding gases exit the bore behind the bullet can do so equally around its preiphery.

    Ian.

  9. #9
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    Quote Originally Posted by Whitebeard View Post
    The shape and angle of a crown has no bearing whatsover on a rifles potential accuracy.
    The most important factor is that the crown is perpendicular to the bore, so that as expanding gases exit the bore behind the bullet can do so equally around its periphery.

    Ian.
    similarly the bullet must leave all the lands at the same time if this doe's not happen you get what we call flyer's. not to bad on a rifle but totally impressive on a 120mm main armament on a tank after a barrel strike

    bob.
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