Never slapped together an AR.

[Vaquero]

I assembled my 1st lower setting in the driver's seat of my truck.
It has a couple of scratches from the framing hammer or the Leatherman pliers.
Idgaf. Neither does the firearm.
It ain't rocket surgery.

 

[jason237m]

I think someone mentioned a vice block, I would suggest the magpul all in one. It's great for building, maintenance etc. I know it's not "bare minimum" but it would be $45 well spent.

https://www.cabelas.com/shop/en/magpul-bev-block-for-ar15m4

 

[SIG_Fiend]

For AR builds, the two most critical areas IMO are the barrel nut and castle nut. Screw either up and you can crack or otherwise damage your receiver.

In terms of tools, for roll pins, if you want to keep things simple and have a single kit, this Wheeler roll pin installation kit will work. You can find much better punches and pin holders elsewhere but, these honestly work fine for most.

For a castle nut wrench, I'd recommend the FCD JCW.

I highly recommend the VISM Lower Receiver Vise Block. It's cheap insurance to ensure you don't crack your lower when torquing the castle nut.

For a GI barrel nut wrench, the FCD CBW is also nice.

I highly recommend using an upper receiver rod for torquing the barrel nut. The Midwest URR is a great option and better than the Geissele equivalent in every way.

For any of these individual tools, yes, you can find cheaper options that are still good. For example, instead of the Midwest URR, the Magpul BEV Block is still a decent option for nearly half the price. That said, if we're talking spending just ~$40 more to get something rock solid and better quality, to me that's worth it.

Also, for the receiver extension and upper receiver threads, I highly recommend grabbing yourself a 14oz tube of Aeroshell 64 (aka 33MS) and lube those threads liberally! That tube will probably last you the rest of your life. I still have a tube from maybe 13yrs ago, and it's still maybe ~95% full after building quite a few AR's in that time.

Here's my latest build:

• Aero slick side upper, LMT MARS-L lower, FCD 2 stage NiB trigger
• KAC SR-25 receiver extension (#25758), VLTOR A5H2 buffer, Geissele Super 42 rifle spring, FCD CN5F
• Daniel Defense 14.5 mid, Centurion 9315 4-prong (pin and weld by John Thomas @ Retro Arms Works, fantastic work!)
• Centurion C4 M-LOK 12"

 

[Kbone70]

I didn't see it mentioned its nice to have a roll pin punch set as well.

 

[Lonesome Dove]

I didn't see it mentioned its nice to have a roll pin punch set as well.

That's called a different variety of Nails ground flat on the ends. Never use Gavanized they bend too easy.

 

[zackmars]

That's called a different variety of Nails ground flat on the ends. Never use Gavanized they bend too easy.

Pfft. Nails? Ain't no one got time for that. I use appropriately sized allen wrenches!

 

[popper]

Torque and stake the castell nut? Never have, not a problem. Many hand guards come with barrel nut and wrench adapter. Make sure your selected upper will accept the handguard, manuf are getting tricky about that.