I have a question about this lower (Cal = Multi)?

quote:

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what does the multi mean? Does it mean it can shoot both 5.56 and .308?

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Short answer, no. A .308 requires an AR-10 lower receiver (larger magazine well, among other differences).

The "Cal-Multi" allows you to configure the lower in a variety of calibers that may be used with the standard AR-15 lower (.223/5.56, 9mm, 6.5mm Grendel , etc.).

EDIT: Quick partial list from ar15.com

AR-15, without bolt modification
.17 Remington
.20 Tactical
.204 Ruger
.221 Fireball
.222 Remington
.222 Remington Magnum
.223 Remington (5.56x45mm)
.223 Remington Ackley Improved
6x45mm
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 BR Remington
6.5mm PPC
6.5mm Grendel
25 WSSM
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)
7.62x39mm
.30 RAR
300 OSM
.357 Auto
.35 Gremlin (necked up 6.5 Grendel to 35)
.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

To be honest, 99 percent of the time lowers are lowers, main difference being forged vs. billet. Some companies may have a nicer finish or tighter tolerances, but as long as you're mil spec you are good to go.

Just read reviews and avoid any companies with bad reputations (R-guns come to mind). I use PSA lowers (paired with BCM uppers) for my builds and haven't been disappointed.

I haven't been perusing the black gun forums in a while but I believe there are really only a handful on manufacturers that produce the raw forged lowers.

EDIT: This thread is old but explains my point about multiple companies using just a few manufacturers.