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Thread: Changing from carbine to mid length handguard...

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    m1ghtysauc3's Avatar
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    Changing from carbine to mid length handguard...

    I'm pretty new to AR15s and don't know much about working on them yet. I'm thinking of switching from a carbine length handguard to a mid length. Probably Yankee Hill. Anyway, what else do I need to buy, besides the handguard itself? Just a gas block? Sorry for the noob question.

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    DJ Niner's Avatar
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    The mid-length carbine is not just about adding a longer handguard; it's about changing the placement of the gas port (hole) in the barrel during the manufacturing process to get a different pressure curve, and moving the gas block or front sight frame to the new gas port location several inches down the barrel, which then requires a longer handguard. I know of no way to make a standard carbine-length gas system into a mid-length gas system without changing the barrel.

    Changing the barrel requires special tools and fixtures (and know-how), and it's far easier (although much more expensive) to just buy a new upper receiver/barrel assembly already manufactured to mid-length specs, and snap it on your existing lower receiver assembly. You can then sell your old upper receiver/barrel group to partially offset the cost of the new upper half.

    Or keep it, and eventually buy a new completed lower assembly to build a second AR...

    ...not that I know anyone who's ever done that.
    "Placement is power" -- seen in an article by Stephen A. Camp
    (RIP, Mr. Camp; you will be remembered, and missed)

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    m1ghtysauc3's Avatar
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    Thanks for replying. I was reading though a different forum and came across a thread with people claiming you can use a mid length on a carbine system by using a low profile gas block. Yankee Hill even makes a claim on their website that their handguards will work with a carbine setup if you use their low profile gas blocks. Am I missing something?

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    DJ Niner's Avatar
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    Well, now I've put myself into the position where I might have to eat my words. Or at least heavily modify my initial response, above. Although you clearly stated in your first post you wanted to switch from a carbine-length handguard to a mid-length, I mis-read your post as you wanting to change to an entire mid-length system, and for that, I apologize. Thanks for clarifying what you actually want to do, and giving the example.

    If the Yankee Hill handguards you referred to were the free-floating vented-tube-type handguards, then they are mounted by threading them onto a special barrel nut. Due to this rigid screw-on mounting system, they need no support at the muzzle end; they will work with any barrel that has a low enough gas block to clear the inside of the tube during installation. Standard plastic handguards need a front and rear mounting point to stay in place, and if you want to install a set of plastic mid-length handguards on your carbine, it will be a bit more complicated.

    I suppose it might be possible to keep the old carbine-length gas system on a carbine by using or switching to a low-profile gas block, and then add a second (non-functional for gas diverting, but functional for locating the front handguard cap) gas block and handguard cap in the proper location for mounting a longer handguard. It might only work with certain handguards that have a large interior diameter for clearance, but I think it could be done. The only potential problem beyond the handguards themselves might lie in the diameter of the barrel at the point the dummy gas block would have to be placed. Gas blocks are bored to a specific inside diameter to very closely match the diameter of the barrel where they are mounted, to prevent excessive gas leakage which might affect reliable functioning. The rest of the barrel, forward of the gas block location, is usually not held to a specific diameter, as there is no reason to do so. The front portion of the barrel is also usually smaller than the gas-block section, so the gas block or front sight frame can be slid into position without scratching/scraping/gouging the finish on the front (exposed to view) part of the barrel. To make this work, you'd have to find a gas block that would fit tightly enough on whatever your barrel diameter is at the point the block needs to be mounted to properly locate the handguard cap for a mid-length handguard. If it was too loose, or loosened during use, your handguards could fall off, which would be a bad thing (loss of weapon control during firing is a serious safety issue; I shouldn't make fun of it, but I did. Bad me).

    If you used a clamp-on-with-screws gas block, it might clamp tight enough (or be able to be modified to clamp tightly enough) to securely locate the handguard cap to get you the combo you want. However, I have a skinny-barrel Colt AR carbine, and I don't think any of the clamp-on gas blocks I've ever seen would clamp tight enough to that skinny part of the barrel to make this work, so it may be "doable" on some guns but not on others.

    Hope this better answered your question. If you decide to do it, let me know how it works out for you (or doesn't, if that is the case).

    Good luck!
    "Placement is power" -- seen in an article by Stephen A. Camp
    (RIP, Mr. Camp; you will be remembered, and missed)

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    m1ghtysauc3's Avatar
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    Yeah I definitely planned on getting a free float. My current handguard is free float but it's a cheap UTG and the carbine length is just too cramped up for me. I feel better with my support arm more extended. I also think the longer handguards look better.

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    DJ Niner's Avatar
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    I have a 16" Dissipator-style AR carbine with a rifle-length 4-rail-free-float tube on it. Plenty of room for gripping or adding gadgets, and plenty of help keeping my hand OFF the hot barrel! Current configuration:

    denner likes this.
    "Placement is power" -- seen in an article by Stephen A. Camp
    (RIP, Mr. Camp; you will be remembered, and missed)

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    m1ghtysauc3's Avatar
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    Oh I see. So you just extended the gas system out further instead of using a low profile.

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    DJ Niner's Avatar
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    That upper was built-to-order at the Bushmaster factory back in 2008 or so (for a friend of mine); they just used their standard Dissipator barrel with a carbine gas system and low-profile gas block, and added the folding front sight gas block just to get the folding sight option. But because it was factory-built, they had the option to match the folding-sight gas block opening to the diameter of the barrel where they wanted to mount it. The options are somewhat dated (most builds of this type would just add a rail-mounted folding front sight nowadays), but well-built.
    "Placement is power" -- seen in an article by Stephen A. Camp
    (RIP, Mr. Camp; you will be remembered, and missed)

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