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Old June 21, 2013, 10:59 PM   #1
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5.56 lower?

Ok, please forgive me if I missed this elsewhere.

What caliber uppers can you put on a milspec 5.56 lower? And what parts do you have to replace? I'm looking for ALL the different calibers....

I think 6.5 Grendel (6.8 ?) .50 Beowulf, 300 Blackout & 5.45 right?
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Old June 21, 2013, 11:22 PM   #2
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Any upper that is also a AR-15. The only part on the lower that sometimes gets changed according to the caliper of upper is maybe a heaver or lighter buffer.
“The problem with socialism is that you eventually run out of other people's money.”

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Old June 22, 2013, 05:26 PM   #3
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AR-15, without bolt modification
.17 Remington
.20 Tactical
.20 Practical
.20 Vartag
.204 Ruger
.221 Fireball
.222 Remington
.222 Remington Magnum
.223 Remington (5.56x45mm)
.223 Remington Ackley Improved
6mm TCU
6mm Whisper
6.5mm Whisper
7mm Whisper
7mm TCU
.300 Whisper (.300/221, .300 Fireball)
.338 Whisper

AR-15, with bolt modification
223 WSSM
5.45x39mm (.21 Genghis)
243 WSSM
6mm PPC
6mm WOA
6mm BR Remington
6mm Hagar
6.5mm PPC
6.5 WSSM
6.5 WOA
6.5mm Grendel
6.8x43mm SPC
.30 Herrett Rimless Tactical (6.8x43mm case trimmed to 41mm and necked up to .308; the 6.8mm version of the .300 Whisper)
.30 RAR
300 OSSM
.357 Auto
.35 Gremlin (necked up 6.5 Grendel to 358)
.358 WSSM (various names, but all are some form of a WSSM necked up to 35 caliber, some are shortened to make them big game legal in Indiana)
.458 SOCOM
.50 Action Express
.50 Beowulf

AR-15 using a simple blowback operation
.17 HMR
.22 LR
.22 WMR
30 Carbine
357 Sig
400 Cor-Bon
41 Action Express
10mm Auto
45 GAP
45 Super
45 Win Mag

This list is in no way complete.

This list does not include complete different uppers like the FN 5.7 or the one that shoots .410 shotgun, crossbow bolts or bolt action uppers like the 50BMG
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Old June 22, 2013, 07:31 PM   #4
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Quentin is right- if it can fit through the magwell then somebody, somewhere, has made an upper that will shoot it.

There's even oddball ones like single shot .50BMG uppers and the 5.7x28mm one that uses PS90 mags and EJECTS down through the magwell.

The AR Rule #39- If it fits, somebody has stuffed it onto an AR-15 platform.
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