First go W/Barrel installed to AR Upper. Advice for what's next?

[VariableRecall]

I've very recently installed my first barrel onto an AR upper provided from a straight shooting Cast Boolits user. It was tricky to align the barrel nut with the gas tube, but it was done to spec and it looks good to me!

I'd like some advice on what I should do next in a matter of ensuring I did the job right, and how I should go along with testing it for the first time.

I believe the first order of business is to get a set of go/no go gauges to determine if I will have a proper headspace between BCG and barrel. If there is actually a problem, what can I do to relieve it? Is that sort of procedure necessary?

Are there any other steps that should be done to ensure that all of the new parts combined with its lower are in working order?

Thanks!

[rancher1913]

make sure the sights are lined up true, this is more important than the gas tube.

[BK7saum]

Headspace is set by barrel extension and bolt. Really not a lot to screw up, it either is in spec or not, based on tolerances, and has nothing to do with the install. I am sure you are good to go. I haven't found any of my builds to be out. Of course I set my dies up based upon the fired headspace to maximize brass life, but all have been good.

[Gtek]

Usually easier to check headspace before barrel install but your past that and as stated, chances are real good it's fine. The one thing that drives me crazy is the lack of attention to gas tube and key alignment on initial builds, slap together and let it run seems to be the theme. When I install tube and before any type of hand guard install this is checked and worked and most if not all can use a tweak.
Remove bolt assembly from carrier and hold upper assembly level and up up, install charging handle and carrier body in upper. Place pinky in rear of carrier and slide in, you will feel key engage tube and then carrier flush to rear of upper. If alignment is incorrect it shifts carrier either a little or a lot causing wear of internal upper and also rapid wear of tube and key. If correct you should get a feel of very light engagement and the slipping in and out with no perceivable jump/shifting in carrier body. A lot of variables are placed in the assembly and rarely does it align correctly. This is the time to tweak and the tweaking will be done out front on tube in the general direction of carrier movement, sometimes two thumbs, sometimes a big screwdriver tip rag wrapped between barrel and tube. The three bends in tube and you are working the center area using the hole in upper as pivot point. I have made a phenolic wedge for internal, sometimes the tube requires a tweak down internally but tube can be removed and adjusted and reinstalled. Sometimes it's a minute or two, sometimes a day or two with the multiple frustrated attempts. Some will not care but this is on of my many "THINGS" that makes me crazy but I know my slick running MSR appreciates it.

[VariableRecall]

make sure the sights are lined up true, this is more important than the gas tube.

Thankfully the barrel's front post/gas was already installed from the factory, so all I had to do was install the gas tube and torque the whole affair into place. I also installed a flash hider on the barrel and that was a first for me as well. I'm pretty sure it's on straight but I suppose I will find out the hard way if that is the case.

[elmacgyver0]

Did the barrel come without the extension?
If it came with the extension installed, just shoot it.
If it is some wildcat that you dreamed up, then yes you need to check headspace.

[VariableRecall]

Did the barrel come without the extension?
If it came with the extension installed, just shoot it.
If it is some wildcat that you dreamed up, then yes you need to check headspace.

The barrel came complete with the Barrel Extension, thankfully. It's a 5.56 barrel as well, and I've got ammo to test it with. I think I'll give it some factory ammo first, then my reloads. The reloads aren't anything special either.