5.56 AR conversions

Would someone be willing to provide a list of calibers that i would be able to convert to and from with my m&p 15…i looked online but cant get a solid answer. I want to be able to shoot different calibers (specifically the new 224 because its amazing) but dont want to have to buy a seperate gun because well im not rich…thanks in advance


Well sadly you will have to get different uppers to shoot the .224, 300 blackout, if your rifle is chambered in 5.56 NATO it can only chamber 5.56/.223 but the lower can be used for .224, 300 BO & others. Forgot you can get a conversion kit for .22 Lr with a different bolt & use the same upper, but as using that upper in the pic for any other calibers besides 5.56 not going to be good idea.


You don’t actually need a complete upper for most conversions if you have an AR barrel wrench. The .300, .224 and .204 Ruger only require a barrel swap. 6.8 SPC or 6.5 Grendel need a barrel, bolt face(but same carrier) and magazine. Going to 9mm(or .357 Sig or .40 or .45 or .22LR) require a new barrel, bolt, carrier, magazines and magazine adapter. There are .22LR conversions that use your existing .223 barrel and conversion magazines that fit the AR mag well. These only need your bolt and carrier swapped.

There is also .50 Beowulf and .458 SOCOM if you’re looking for big bore fun. These use proprietary uppers. Hope that helps.


So all i would need to buy to shoot .224 is a different barrel and obviously the wrench to swap them correct? Your reply had alot of info i just want to be sure before i commit to anything…if im gonna buy a new upper and all the other shit i may as well just find another gun but i really dont want to have to do that…

Why would it not be a good idea? Is it because of preasure differences and things like that?

Yes, just a barrel swap for .224, .300 and .204. Pressure is not an issue in the AR upper, as the bolt locks into the barrel extension rather than the receiver like on most bolt actions. I believe @RangetimeFun is assuming that is the factory M&P-15 sport upper. It will function fine with any of the above calibers but may not be suitable for maximum accuracy, which the .224 and .204 are designed for.

I was referring to the barrel, I know you cannot shoot 300 BO out of a 556 barrel. Not sure about .224 out of a 556 barrel. I also agree that the calibers .224 & other might shoot out of a 556 barrel which is what is installed on the M&P 15 Sport II rifle. I would never recommend shooting any different calibers out of a rifle not stated or marked for that caliber.
The upper itself can without the barrel can be used with any other barrel. See with different caliber you get different throat sizes & chamber sizes. Your M&P lower will & can be used for other caliber’s like 300 BO cause they use the same magazines.

A company from England just released a 22 WMR upper to fit the AR-15 lower, about time I say

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I’ve seen a 22-250 in the AR10 platform . . . so many options.