Home CMMG Smyth Busters: Can an AR-15 Fire Full Auto With an M16 Carrier?

Smyth Busters: Can an AR-15 Fire Full Auto With an M16 Carrier?

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Brownells Gun Techs Caleb and Steve are back for a “fact or fiction” discussion about full-auto AR-15 parts, specifically the bolt / carrier group (BCG). The guys explain the difference between a full-auto M16-type BCG and a semi-auto one: the full-auto has a longer shroud on the underside to trip the auto sear. If you drop an M16 bolt / carrier group into your semi-auto AR, it’ll shoot full auto, right? NOPE! It doesn’t have any of the other internal components needed to operate full auto. (Interesting fact: Brownells sells a fair number of full-auto to semi-auto conversion kits to local law enforcement agencies that receive surplus military M16s through the Department of Homeland Security.) So the notion that installing an M16 BCG and/or a couple other full-auto parts in your AR-15 will turn it into a machine gun is… a MYTH. Busted.

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42 COMMENTS

  1. Step 1: Buy an AR15
    Step 2: Weld a metal plate on the bolt carier, mill a groove, file and polish it
    Step 3: Buy the M16 lower internal parts
    Step 4: 3D print an M16 lower
    Step 5: You have an Automatic AR15/M16

  2. Very few people also know that the UPPER has to have the proper cut out to allow room for an auto sear. Some AR uppers will not work on a full auto m16 lower, even with the full auto bcg installed.

  3. For what it's worth an M-16 can NEVER be converted to an AR-15…………. Even if you change all the parts the sear pin hole is still there! These folks are NUTS and now you should NEVER believe another word they post…………

  4. Swiftlink/lightning link ✅ enhanced/m16 bcg ✅ no need sto swap fcg components. This is all hypothetical of course. Thanks to the NFA, and other INFRINGREMENT AGENCIES for keeping us safe with operations like Fast and Furious and Waco. Hats off commies. 👏

  5. Everyone wants a full auto AR-15. What in the hell for? In 13 months in Vietnam I didn't put my M-16 on rock and roll more than once or twice. You didn't need a machine gun.

  6. The auto sear was designed to slow down the cyclic rate. Direct gas impingement closed bolt was never designed to be full auto. The US Government in their wisdom wanted it to be full auto.

  7. For those who still struggle to understand the US Federal gun laws (and I mean Federal, not the state ones, which are often impossible to understand at all) — it is perfectlly LEGAL to have any M-16 full auto parts in your AR-15 except the auto sear. Don't be fulled by those "intent to build" fairy tales. As long as you DO NOT drill the third hole in your lower and isntall an auto sear, you are just fine with the rest of military specs parts.

  8. It just takes a little finesse with the lower receiver, and the right trigger and bolt carrier. If you know the dimensions of the M16 lower, you can just drill and route them in when finishing your 80% lower. Or mod your factory lower. But who wants a serial number on their gun anyway?

  9. Wonder how much they got paid to persuade people to not get a full auto conversation kit also known as a paperweight and the die to drill the third hole and mill out a pocket into the receiver no more than .125 thousandths on the outer walls👀oops I said too much

  10. There is absolutely no reason to convert your rifle to Full Auto. If the "crunch" ever does come, just smack somebody over the head and take his!

    Repeal the "Hughes Amendment!" Hell … repeal the whole damned NFA!

  11. A lot of rifles come with the M-4 bolt stock, mine did. And it was a fairly cheap AR-15. It certainly isn't full auto lol. Just means the bolt is a bit more beefy is all.

  12. The carrier, safety, trigger, disconnect and hammer are all different on an actual M-16. Take away any single component and you have a semi-auto rifle. I think the full-auto parts in the lower receiver are illegal to own as well.

  13. Can anyone list what parts are illegal to possess under federal NFA regulations. On an AK as long as there is not the third pin hole from what I understand there are no federal regulations. What is the case for the AR relative to illegal machinegun parts? Good to know that there is a wall thickness difference between the AR and M16 lower receivers.

  14. You can't do it. Period. Full Stop…….
    (Unless you really know what you're doing……then you can).
    And owning parts that are not installed might not mean you actually own a Full auto….It could just be you have some parts that might come in handy during a zombie apocalypse.

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