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Thread: Question of Length- Cutting an M4 Barrel

  1. #11
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    Quote Originally Posted by Safetyhit View Post
    The less than ideal possible outcomes could include an uneven crown or a misaligned gas port.
    If the OP were to do the work him in his garage with a hacksaw and Dremel, I suppose these outcomes would be possible. I guess I'm making the assumption he either possess the tools and skill necessary to do it or intends to send it to a shop that does.

    Either way, the crown will come out just fine, and the gas port isn't moving, so misalignment isn't possible.

  2. #12
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    Quote Originally Posted by Dead Man View Post
    If the OP were to do the work him in his garage with a hacksaw and Dremel, I suppose these outcomes would be possible. I guess I'm making the assumption he either possess the tools and skill necessary to do it or intends to send it to a shop that does.
    Assumptions can be problematic and even good gunsmiths make mistakes. Assuming he knows a good gunsmith.

    Quote Originally Posted by Dead Man View Post
    Either way, the crown will come out just fine, and the gas port isn't moving, so misalignment isn't possible.
    How do you know the crown will come out just fine? And are we not talking relocating the FSB? Also, what about the potential for a less than perfect thread job?

    You're making it sound essentially risk free and that simply isn't the case. Not looking to nitpick but there's no other way to put it.

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    I'm weighing out options. I'm thinking I could get a complete Colt 6920 to SBR. The 16" bbl with the carbine length gas system starts off with a smaller gas port for when I get a suppressor and would allow me to shoot the rifle until the SBR paperwork clears. Just thinking it might be a practical alternative to ordering a bbl with a custom gas port size. I really like how Grant set up his dual purpose SBR in this thread-
    https://www.m4carbine.net/showthread.php?t=33743

    Going this route would give me more control over port size and concentricity of the threads to reduce POI shift when shooting with or without the suppressor.

    Thanks for the responses. I don't have an M4 bbl to measure
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  4. #14
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    Quote Originally Posted by Safetyhit View Post
    Assumptions can be problematic and even good gunsmiths make mistakes. Assuming he knows a good gunsmith.



    How do you know the crown will come out just fine? And are we not talking relocating the FSB? Also, what about the potential for a less than perfect thread job?

    You're making it sound essentially risk free and that simply isn't the case. Not looking to nitpick but there's no other way to put it.
    FSB does not need to be relocated, the port simply needs to be widened about a hundredth of an inch. The crown and threads can be cut just as easily as from the manufacturer. Can you get a bad barrel from the manufacturer? It happens. Can you get a bad cut from a qualified shop? Less likely, but it also happens.

    This isn't an arcane art- it's a very common service. Problems are uncommon.

  5. #15
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    Quote Originally Posted by Safetyhit View Post
    Assumptions can be problematic and even good gunsmiths make mistakes. Assuming he knows a good gunsmith.



    How do you know the crown will come out just fine? And are we not talking relocating the FSB? Also, what about the potential for a less than perfect thread job?

    You're making it sound essentially risk free and that simply isn't the case. Not looking to nitpick but there's no other way to put it.
    Cutting & crowning the barrel isn't that difficult and if I were simply planning to use an A2 birdcage, I could probably figure out how to re-thread the muzzle
    INSIDE PLAN OF BOX
    1. ROAD-RUNNER LIFTS GLASS OF WATER- PULLING UP MATCH
    2. MATCH SCRATCHES ON MATCH-BOX
    3. MATCH LIGHTS FUSE TO TNT
    4. BOOM!
    5. HA-HA!!

    -WILE E. COYOTE, AUTHOR OF "EVERYTHING I NEEDED TO KNOW IN LIFE, I LEARNED FROM GOLDBERG & MURPHY"

    http://i115.photobucket.com/albums/n289/SgtSongDog/AR%20Carbine/DSC_0114.jpg
    I am American

  6. #16
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    Quote Originally Posted by Dead Man View Post
    FSB does not need to be relocated, the port simply needs to be widened about a hundredth of an inch. The crown and threads can be cut just as easily as from the manufacturer. Can you get a bad barrel from the manufacturer? It happens. Can you get a bad cut from a qualified shop? Less likely, but it also happens.

    This isn't an arcane art- it's a very common service. Problems are uncommon.

    My ASSumption (told you they can be problematic) was that if you are going past the M4 notch then there would not be adequate room for threading leaving the FSB in place, but looking at one now I see that isn't necessarily true I suppose. Still there is risk, even if minimal, and it will cost money unless you take further risk and do it yourself. But it's not my decision and so be it.

    This discussion reminds me of a similar thread that highlighted some of what I mentioned. Will see if I can find and then post the link.

  7. #17
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    Robb Jensen successfully cut down a barrel with an M203 notch on it and turned it into an SBR. You may want to contact him and see what all he did.

  8. #18
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    Safetyhit. Please take the drama back to the GD Area. What Dead man stated earlier was essentially true. A competent shop can do what is required. As to whether the cost of it is worth it, probably not.



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  9. #19
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    Quote Originally Posted by Iraqgunz View Post
    Safetyhit. Please take the drama back to the GD Area. What Dead man stated earlier was essentially true. A competent shop can do what is required. As to whether the cost of it is worth it, probably not.

    Hey thanks IG. I'll suppose this comment has nothing to do with the cologne thread and try to clarify a bit further.

    Here is the old thread I was referring to. The question was about the feasibility of cutting a 16" M4 down to a 12.5" and sure enough there you are in the first post stating "My advice is not to cut the Colt barrel." and it went on from there.

    Others you would perhaps deem more reputable chimed in, agreed and even mentioned some of my same stated concerns.

    https://www.m4carbine.net/archive/in...p/t-75063.html

  10. #20
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    The barrel at the notch should be 0.61 dia - if you square off the tapered step at the back of the notch, then cut and thread the "notch" section of the barrel, you should come out with a barrel that is ~11.3 inches, measured from the bolt face.
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