Dumb question about AR-15 uppers

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ACP

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Sorry in advance for my ignorance, but I believe I'm in the right place for answers:

I have an older Bushmaster XM-15 "Patrolman's Carbine" in 5.56.

What other caliber uppers can I put on it?

I'm guessing .308 is a NO due to magazine well size, frame size, etc.
 
.308 is a no go. You can find including but not limited to:
.204 Ruger
.223 Rem
6x45
6.8 SPC
7.62x39
9mm
300 Blackout
450 Bushmaster
458 SOCOM
50 Beowolf

I am sure there are some I forgot besides 5.56.
 
I'm guessing .308 is a NO due to magazine well size, frame size, etc.
That's correct.

What other caliber uppers can I put on it?
.22 LR is probably the most common conversion. The most popular alternative center fire rifle calibers are 6.8 SPC II, and .300 BLK. 7.62x39 and 5.45x39 are even fairly common. .204 Ruger is another common one. Then there are the short fat single stack cartridges like .450 Bushmaster, .458 SOCOM, .50 Beowulf, etc. Of course there are also the fairly common pistol caliber uppers in 9mm and .45 ACP that generally use a block in the magazine well to hold Colt SMG, UZI, or similar mags. That's the common stuff. Just about anything that will fit in the mag well has been made. There were (are?) even single shot bolt action .50 BMG uppers that single loaded on the side of the upper.
 
The WSSM is an interesting round to me, and I may build an AR in one of those calibers. There are also .410 bore shotgun uppers.
 
There is a 50BMG upper for an ar15 plus 50 or so other calibers. The upper has really nothing to do with it. It is the barrel and extension reamed and head spaced properly to fit the cartridge you desire. Then the bolt needs to fit the rim of the cartridge and be matched to the head space. The only limitation has been touched on, the length of the cartridge must be able to eject and feed from the mag for semi auto function. The 50BMG is actually a bolt action upper. It is the exception to the rule as it is a caliber specific upper.
 
Also 6.5 Grendel and 17 Remington

There are a number of wildcats based on the 6.8 SPC case and the Grendel case.
 
The WSSM is an interesting round to me, and I may build an AR in one of those calibers. There are also .410 bore shotgun uppers.
i have one that is .358. I use .24 cases necked up to .358. Great deer whacker

If you go to Dedicated Technologies website, he has a variety of exotic stuff. The .358 is legal in Indiana for deer
 
I have a 7.62x25 upper... and wish those surplus spam cans were still available...
 
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