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Converting an AR carbine length barrel to midlength

Discussion in 'Rifle Country' started by JustinJ, May 26, 2015.

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  1. JustinJ

    JustinJ Member

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    Has anybody ever tried to convert an existing AR barrel with carbine length gas system to a mid, or even rifle length? Drilling the new gas port is straight forward enough, i assume, but sealing the existing carbine length port is the tricky part. I've considered a low profile gas block installed upside down but suspect there may still be some gas leakage. Would a quick mig weld warp or disrupt the barrel is some other way? Possible drill and tap the carbine length port to the smallest screw size available?
     
  2. Taurus 617 CCW

    Taurus 617 CCW Member

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    I suppose it could be possible but I have never heard of either procedure being done before. You will have to make sure you don't get any welding slag inside the barrel or it is going to be difficult to remove. The drill and tap method may be a better option.
     
  3. Tirod

    Tirod Member

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    It's machinist level work to drill a new port at exactly the right vertical location precisely on the midlength barrel port position. Add plugging the old hole, which has been posted on arfcom to be done with a bit of electric welding.

    All that work will likely cost as much as a new barrel already set up. The incremental difference in timing won't pay back over the life of the weapon in softer recoil or slower cycling speeds.

    Buying a barrel with the correct port location for timing that length barrel is important. Carbine length gas on a 16" wasn't optimal and still isn't, entirely why the makers invented and moved to midlength for it. It's been arguable there's a significant difference, but there it is - they went to the effort and did it anyway. After all, they were the ones footing the bill in the QC department and having returns, much less the impact on their market brand.

    Shoot what you have anyway, it makes an incremental difference that is hard to measure, but it's there. Most won't ever see it shooting less than a thousand rounds a year.

    It can be done, but just because you can doesn't mean you should. Add up the costs and buying a gun set up correctly for 16" barrels is money ahead.
     
  4. ClemY

    ClemY Member

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    If you feel your carbine length system is over gassed, several possible solutions are available. An adjustable gas block is one way. The first and easiest way is to use a heavier buffer. My 16" mid-length guns both have 5.4 oz. buffers and work great.
     
  5. MachIVshooter

    MachIVshooter Member

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    The barrel OD is smaller forward of the gas block; in addition to plugging the old port and drilling a new one, you'd also have to fan a custom gas block to fit the smaller diameter (~0.720" on gov't profile tubes).

    You can buy 4140 middy barrels for $100, as little as $130 chrome lined 4150. Not worth the effort to mod a carbine gas barrel.
     
  6. DougW

    DougW Member

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    Cheaper and easier to just buy a new barrel.
     
  7. rcmodel

    rcmodel Member in memoriam

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    Fogadaboutit!!

    Welding is likely to warp the barrel and make it shoot goofy groups.

    Plugging it with a screw is likely to end in a series of unfortunate events.

    As noted, machineing a new gas block to fit the smaller barrel forward of the old gas port position would cost more then a new barrel anyway.

    rc
     
  8. benEzra

    benEzra Moderator Emeritus

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    If you buy a midlength barrel and sell your old barrel to recoup some of the cost, you can be under $100 net for the new barrel.
     
  9. NWcityguy2

    NWcityguy2 Member

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    Or if your barrel is 16", chop it down to 14.5" and permanently attach a muzzle device. It would still be easier to buy the mid-length though.
     
  10. JustinJ

    JustinJ Member

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    I have a drill press and vice for exacting alignment. Electric wielding includes quite a few different types. Do you recall which they used? I have a mig welder but suppose a tig welder would be needed to ensure the barrel isn't damaged.

    I do actually have an adjustable gas block but its a pain to adjust because i have a midlength forearm on it. It's also a host weapon for a quick detach suppressor so i need to be able to adjust accordingly.

    Its a pencil barrel so i think the OD of the barrel is .625 everywhere but I'd have to check.

    Yeah, i know, but the rifle is a Colt 6720 which i heavily customized and i'd like to retain the original Colt barrel on the rifle. However, I've been thinking about building an SBR so maybe i'll just use this rifle for such and have the barrel cut to 14.5 so the carbine gas system will be matched with the right barrel length. I do have a bandsaw after all....JK

    Thanks to all for the replies.
     
  11. Sam1911

    Sam1911 Moderator Emeritus

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    Well, heavily modifying a barrel sort of evaporates the "original Colt-ness" of it. Drilling, tapping, welding, plugging, etc. pretty much moves your barrel out of the "Colt Mil-Spec" category. The value of it being that one thing is gone because the alterations have made it some other things. For better or worse.
     
  12. JustinJ

    JustinJ Member

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    As its a 16" barrel it never actually fell into the milspec category to begin. Monetary value is not a concern either, but rather configuring the rifle to my desired specs while keeping it Colt "where it counts", per my personal preference.
     
  13. boom boom
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    boom boom Moderator Staff Member

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    Why not just catch one of the specials that Palmetto State Armory has on skimpy uppers with a mid length barrel, gas tube and block, and delta ring. Have seen them for a little less than $200. Or just build another upper and keep the original upper for Colt resale value.
     
  14. Hookeye

    Hookeye Member

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    Make a sleeve to go over the port area. Could Loctite, epoxy or silver solder in place.

    Could D&T and use threaded plug for the port, secure by Loctite or little weld.

    BTW, I've run 16" CARs for decades, never a problem. But all 1 in 9 and running 55 gr stuff.
     
    Last edited: May 30, 2015
  15. kwg020

    kwg020 Member

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    boom boom had it right. Get a cheap upper and wear it out and keep your Colt upper in the gun safe.

    kwg
     
  16. henschman

    henschman Member

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    Lots of people would pay good money for that rifle, or just the upper. I say sell it and buy a new mid length pencil profile upper/rifle from BCM, DD, or PSA if thats what you want. Any of those would be chrome lined, 4150, and HPT/MPI just like a Colt. PSA has a whole mid ultralight rifle kit right now for $550 that has a CHF FN barrel.
     
  17. JustinJ

    JustinJ Member

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    I like that idea. The sleeve would be concealed by the handguard well enough.

    It runs well and perfectly reliable but in addition to reduced recoil, i'm thinking midlength would help reduce backpressure and blowback with the can.
     
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