AR-15 Upper build - Anyone Do It? Is it worth it?

I recently built my first AR lower from a kit. I enjoyed the process, and it wasn’t too difficult. I paired this lower with a pre-assembled upper, and it works great.
I’m considering my next AR build at some point in the future, and thought about doing a “complete” build from parts. The upper seems a good deal more complicated than the lower, with more potential for problems. Does it require any expensive tools?
Has anyone done this? I’m OK with a challenge and I am good with mechanical projects , but I’m not a gunsmith. I just don’t want to (a) get in over my head, (b) spend way more than a pre- assembled upper, or (c) have the upper blow up on me :grimacing:.
Any recommendations?


YAH, how about (d) ALL OF THE ABOVE. I would seek for that info with a pro gunsmith shop if there’s one in your area, or google for advice.

1 Like

I’ve never assembled one from scratch, but I have swapped a barrel out. A vise and an AR upper block made it a lot easier. The block is fairly economical and I am glad I bought the lower block in a kit as the lower block comes in handy as well:

You will need an armourer wrench and a torque wrench as well. I personally think assembling the lower with the assortment of springs that get away from you is more challenging - assuming you have the proper tools available.

This is a pretty good tutorial on AR Upper assembly process: How to Build an AR-15 Upper Receiver: Ultimate Visual Guide - Pew Pew Tactical

Edit: Just noticed the Pew Pew Tactical article has a link to a different type of upper holding block you might like better, I would prefer it if I didn’t already have the one I pictured …


I have assembled a number of them. I get what I want in the configuration I want. Sometimes it is a bit less expensive, sometimes not. Heck, my wife built hers too… I think it is easier than assembling the lower, but neither one is really all that hard with the right tools, as explained above.


Assembling an upper is no more difficult than the lower other than the need for bench blocks and a fair size vice/bench to hold the upper still. I have a block similar to @Gary_H but mine has a “inner filler” piece that slides in place so you cant crush the upper. Lots of folks that have never done it get twisted around the axle about “headspace”. On an AR either the bolt rotates home and locks or it doesn’t simple as that. You don’t need head space gauges.

Tips and tricks:
Lube the SNOT out of your locking ring/fore arm block/what ever its called this week (referred to here after as the “nut”) prior to install. Screw it on as tight as you can reasonably get it, like “Grunt” lbs of force. Then take it off, clean it, lube it and do it again. Repeat the last step again. That’s three times if you lost count.

NOW, clean the upper, barrel and block with brake cleaner and scrub the threads with a tooth brush, clean with brake cleaner again. Once it’s bone dry. Dip your finger in some motor oil and rub it on the threaded parts (there’s only two). Run a dry paper towel around both threads and clean off the excess oil.

This is the final torque. Torque wrench be dogged it’s going to be what it is to get it aligned. You are to get the gas tube holes lined up WITHOUT backing off the nut. Not as easy as it sounds but you can muscle about 7/8ths of a tooth/hole if you go slow and apply increasing force. Cheater bars on your wrench are acceptable. Your gas tube MUST be clear of all obstructions and “float” as it comes into the upper, that is the hardest part.

What you are doing is “Crush mating” your parts. They all come with some kind of coating be it anodizing, phosphate, blue, stainless, paint or parkerizing there is something coating it and you are literally crushing it flat and smooth with the first three steps.

Flash suppressors use the same logic except that you can sand a crush washer to get the muzzle device to index correctly with “grunt lbs of force”.

All the other bits, unless you are building A2 sights, are rudimentary.

Final take away is NEVER back off a crush fit part for final fit. If you go over and can’t get to the next aligned hole take it of clean it and do it again.

Final, Final take away, ALWAYS MAKE SURE YOUR WRENCH IS FLAT AGAINST THE PART AND FULLY ENGAGED. Even if you don’t think it wiggled re set it and get it flat and flush.

Happy building! It’s Lego’s for big kids!!




I totally agree with craig6 follow his advise and you will be fine.


Thanks for all of the great tips! Looking forward to a new project soon!