40 S & W or 9mm AR-15's

[Wea300mag]

I have an extra AR-15 stripped lower and want to build something unique with it. I have a 5.56 and a 6.5 Grendel. I was thinking of building one using a caliber typically used with handguns. I would appreciate any opinions on the handgun caliber option or other options you can think of.

Thanks

[Austrian Hunter]

.50 cal.  You can get an upper and mag and you set. 

[jay.sharkbait]

10mm

[Button Nubbs]

10mm

would be sooooo sick but ammo will make ya go broke!

[Fisherdave10]

I would go with 9mm.  Ammo costs less and "high capacity assault clip" magazines are more common IMO.

[NW-GSP]

You can reload 10mm for $13 a box of fifty

[Huntboy]

I would go with 9mm.  Ammo costs less and "high capacity assault clip" magazines are more common IMO.

 

[carpsniperg2]

Another fairly cheap round and a lot of fun is the 300 blackout.