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Discussion Starter #1
as the title says how many different calibers uppers can use the 556 lower. just wondering what my options are.
 

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.22lr, .223/5.56, 6.5, 6.8, .450 Bushy, 9mm, .40, 10mm, .45, 5.45x39, 7.62x39, 50 Beowulf, just to name the common ones. I'm sure someone will be along shortly to add more, like the .458 Socom, etc.
 

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You mean the AR lower, right? Not the SIG 556?

Ghillie's right - just about any caliber that fits the mag well, and some that don't. You can get a 50 BMG bolt-action upper for your AR lower if you want. Or you could go all the way down to 5.7 FN, where the mag well becomes the ejection port! .204 Ruger is a pretty common one...
 

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.204.....I knew there was a popular one I was forgetting. :D I was distracted by the fact that the Illini football team was actually dominating the game for once. :mrgreen:
 

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as the title says how many different calibers uppers can use the 556 lower. just wondering what my options are.
Huh...you might ask what your options are NOT. Here goes (remember some of these are serious wildcat cartridges you won't find in your average AR parts/accessories catalog, but they work 100% in standard AR-15 lowers):

17HMR
.17Mach2
.22lr
.222 Remington
.25 WSSM
.204 Ruger
6.5 Grendel
7.62x39
5.56x42(SPC)cat
6x41(SPC)cat
6mmBanshee(Grendel cat)
6.5 Banshee(Grendel cat)
6.8SPC
6mmWOA
6mm Hagar
6mmAR
6mmAR turbo
458 socom
50 beowolf
338 spector
30HRT
300 Whisper
6mm/223
25/223
30/223
10mm
45acp
9mm
40 S&W
6BR
6BRX
6mmPPC
223WSSM
243WSSM
25WSSM
358WSSM
(.50 BMG, .50 DTC, 408 Chey Tac, 338 Lapua Mag - for conversion uppers not using the AR-15's mag well...may require modification to fire control components, etc.)
 

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Discussion Starter #7
wow lots to choose from. the 6.5 grendel upper is about 500 bucks from centerfire i was thinking of getting that for deer hunting. was just wondering if my stock lower would work. thx for the info
 

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The Grendel rifles are VERY nice and the 6.5mm round is just a wicked little bugger...especially with the 123gr Lapua Scenar loads out of at least an 18" barrel!! There is a great site dedicated to the 6.5 Grendel with tons of excellent information. If you have not happened upon it yet...check it out:

6.5 Grendel Fan Site :: For the 6.5 Grendel Aficionado

Also, Alexander Arms and several other sites have a lot of great information.
 

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Any reloading manual will have cartridge dimensions for the .223/5.56x45. Any round with an overall length equal to or less than the .223/5.56x45 will be able to use the existing magwell. My personal favorite is the .300 Whisper, the Whisper uses .223 brass cut off near the shoulder and necked down (doable with about $100 worth of reloading equipment) to .30 caliber and firing the .308 bullet. You can load 240 grain .308 bullets subsonic or supersonic. Similar ballistic performance to 7.62x39 but if you spend the money on a .308 supressor and load subsonic the rounds are VERY quiet! The ONLY part on a .300 Whisper upper reciever that is different from a standard AR15/M16 is the .30 caliber barrell, you can use your standard AR magazines and the boltface is the same so parts are readily available (brass, bullets, reciever and BCG)

The 6.5 Grendel is also attractive because it uses many parts in common with the AR15/M16 and with a drastically higher ballistic coefficient the 6.5 Grendel is flatter shooting than the .308 and has more kinetic energy so out past 5-600 yards the 6.5 Grendel hits harder.
 
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