We all say were only gonna do just one build , Wake up your lieing to yourself , It wont ever happen one turns into two , two turns into three, you get my point .
Hell just a month ago I was looking at my first AR trying to figure out what I wanted and I knew nothing about them , Now working on building a third already . WTH !!!
About 2-3/8 x 7/8" not counting the a full length guide along one 7/8" side (which you wouldn't need). And maybe 5" long. You might just look for a junker magazine to use instead. Or if you have Sportman's Warehouse nearby look for one of their $3.99 20rd Thermolds or add one to an online order.
__________________ US Army 1966-69, VFW Life Member, Retired Geek
If some of you are torquing your muzzle device with the receiver in a block, you somehow avoided a common problem - over torquing the barrel alignment pin.
To the OP - somewhere in there should be something to hold the barrel in the vice to install said muzzle device