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Thread: Name & Use Of This Part Of Bolt?

  1. #21
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    The angle in question is the lead-in surface to allow the bolt to cam into the locking lugs of the barrel extension. The little angle cut you see is a manufacturing artifact that happens, probably because the mil specs don't address just how big or small that cut can/is allowed to be.

    You can be snarky and say it is sloppy set-up by the CNC operator or path cutter programmer, but if it doesn't decrease strength, and isn't addressed by the mil specs, no-one involved cares one whit for your snark.

  2. #22
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    Quote Originally Posted by patrick sweeney View Post
    The angle in question is the lead-in surface to allow the bolt to cam into the locking lugs of the barrel extension. The little angle cut you see is a manufacturing artifact that happens, probably because the mil specs don't address just how big or small that cut can/is allowed to be.

    You can be snarky and say it is sloppy set-up by the CNC operator or path cutter programmer, but if it doesn't decrease strength, and isn't addressed by the mil specs, no-one involved cares one whit for your snark.
    So, is there a commercial equivalent to the FN bolt with the lead-in surfaces?
    [EDIT: Nevermind, I think I've found one, complete with half moon cuts.]

    I am not interested in a completely redesigned BCG (as is easily found) but I am interested in the availability of a new bolt of milspec quality with the FN-like lead-in surfaces.
    [EDIT: Nevermind, I think I've found one, not milspec but quite reputable.]
    Last edited by catargadelendaest; 09-04-10 at 04:08.

  3. #23
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    I'm not sure I follow. A mil-spec bolt will have a lead-in angle cut on the lug corners, simply as part of the drawings (and for good engineering reasons, to improve reliability and longevity).

    Colt, FN, anyone who makes .mil bolts will have a lead-in cut. The little "tail" cut you see on the bolt body is inconsequential to function or strength.

  4. #24
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    Quote Originally Posted by patrick sweeney View Post
    The angle in question is the lead-in surface to allow the bolt to cam into the locking lugs of the barrel extension. The little angle cut you see is a manufacturing artifact that happens, probably because the mil specs don't address just how big or small that cut can/is allowed to be.

    You can be snarky and say it is sloppy set-up by the CNC operator or path cutter programmer, but if it doesn't decrease strength, and isn't addressed by the mil specs, no-one involved cares one whit for your snark.
    defensive much? simply pointing out exactly what it is- machining slop- is not necessarily "snarky," and in this instance, i don't believe anyone has been snide.

    it's a fact- whatever you want to call it. pick a different name- "inconsequential production machining variances," if you prefer that. nobody said, "see the BULLSHIT colt produces? **** those guys." we're simply explaining what the marks are.

    smoke a bowl or something.

  5. #25
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    I appreciate fine machining as much as the next guy. But if the drawings, inspection standards and mechanical function do not require it, a manufacturer is not going to lose much sleep over cosmetic differences.

  6. #26
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    With the capabilities of modern CNC controls....tooling marks should be able to easily be avoided. I know they dont' affect the function of the part, but they are easily avoided by keeping up with tooling offsets. JMO

  7. #27
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    Those cuts are not due to CNC errors, required lead ins, slop, or anything else. They are there for a specific purpose as they show up on various manufacturer's bolts. With my many years in the machine tool business, cutting the simple lugs on an AR15 bolt in no way requires any sort of lead in cut that would create the marks in question.

    Eventually some one will chime in with a well researched answer.
    Last edited by Singlestack Wonder; 09-01-10 at 19:18.

  8. #28
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    Quote Originally Posted by Singlestack Wonder View Post
    Those cuts are not due to CNC errors, required lead ins, slop, or anything else. They are there for a specific purpose as they show up on various manufacturer's bolts. With my many years in the machine tool business, cutting the simple lugs on an AR15 bolt in no way requires any sort of lead in cut that would create the marks in question.

    Eventually some one will chime in with a well researched answer.
    "those cuts?" gotta be more specific. the half-moon cuts might very well serve a purpose... i sort of doubt it, but they're the only marks out of all this that we've talked about that show up consistently on different manfer's bolts (which actually probably all come from FN).

  9. #29
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    Quote Originally Posted by bkb0000 View Post
    "those cuts?" gotta be more specific. the half-moon cuts might very well serve a purpose... i sort of doubt it, but they're the only marks out of all this that we've talked about that show up consistently on different manfer's bolts (which actually probably all come from FN).
    As I stated in a previous post about the 'half moon" cuts, I believe they are there to allow debris to be channeled out of the lug lockup area. And, due to the fact that they show up on various manufacturer's bolts, they are defintiely there for a purpose.
    Last edited by Singlestack Wonder; 09-01-10 at 19:32.

  10. #30
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    pulled my BCM bolt.
    it doesn't have the half moon cuts.
    FWIW

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