DIY AR-15 Build: Upper Receiver Assembly Introduction - ITS Tactical

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DIY AR-15 Build: Upper Receiver Assembly Introduction

By The ITS Crew

1 of 8 in the series DIY AR-15 Build Upper

Welcome back to our DIY AR-15 Build and the start of our tutorials on assembling your Upper Receiver and finishing the build!

In this article we’re going to re-address all the parts and tools you’re going to need to assemble your Upper Receiver. While there are many complete uppers out there to purchase, we’ll be taking you through a complete upper assembly.

From the forward assist to the compensator and everything in between, when we’re done with this second series you’ll have all the resources available to you to take an AR-15 build from the ground up! Let’s get started!

Upper Receiver Introduction

In this series of articles on the Upper Receiver assembly there’s a whole lot to discuss and many things to consider when you’re selecting the parts that will go into your upper. Today we’re simply going to discuss the proper tools and the parts that we’ve selected for our 14.5″ Direct Gas Impingement Hybrid AR-15 build.

We’ll save the individual assembly articles for what to consider at each stage of the build and why. For an in-depth look into the tool selection we’ll highlight below, please refer to the initial introduction article to the DIY AR-15 Build.

While we’ve also referenced the parts we’re using in the original intro article, we’ve broken the list down a bit here to further highlight the individual pieces should you choose to undertake a ground up upper build like we’ll be going through in all these upcoming upper articles.

DIY AR-15 Build: Upper Receiver Assembly Introduction


Something to note here before we get into the parts list is to ensure you’re aware that the stripped parts we’re linking to in regards to the barrel will require a gunsmith to drill the holes for the taper pins and the pins themselves are not included here on our parts list.

With our 14.5″ barrel you’ll also need to get a gunsmith to permanantely affix the BattleComp 1.5 that we’re using in this build to satisfy the requirements of the National Firearms Act. Permananetly affixing the 1.5″ BattleComp brings the barrel length to the required 16″ length without having to apply for a SBR and pay the $200 Tax Stamp.

Below you’ll find links to the “Group” part (in bold) as well as the individual parts contained in the group in a sub-category below it. Some sub-category listings are simply features of the group.

DIY AR-15 Build: Upper Receiver Assembly Introduction


DIY AR-15 Build: Upper Receiver Assembly Introduction

Stay tuned next week as we continue our DIY AR-15 Build with the first part of our Upper Receiver assembly installing the Ejection Port Cover and Forward Assist!

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  • Defiantly get the correct tools. I cracked my Colt upper when I was attempting to take my barrel off by not using a upper receiver block. I ended up having to put the upper in the freezer to break the barrel nut loose.

    • LOL I remember when you said that happened! Yes, don’t pull an Eric!!

    • Yeah I pulled a Munson on that one!

  • I don’t understand the 14.5″ barrel length for civilian use.

    If we need to permanently attached a compensator to reach a 16″ length, why not just get a 16″ mid length BCM upper? In theory you’ll get a nudge more velocity with the longer barrel and you effectively have the same size rifle in the end.

    I’m very much a newbie, so if I’m off based please educate me.

    • mmasse

      I was thinking the same thing about the upper. If a 16′” length gas systems help create a slower bolt cycle and saves wear and tear on the internals why would I want a 14.5″ barrel?

    • Manny

      Sean, after adding the compensator a 16″ barrel ends up being about 17.5″. Lots of people like having the shortest possible AR they can get without getting an SBR stamp. Also, the 14.5″ barrel is the size on the M4, so lots of people that want military correct rifles get 14.5″ barrels and weld on the compensator/flash hider.

      mmasse, there is no such thing as a 16″ length gas system. I think you mean a mid length gas system (of which the gas tube is about 9.5″ long) that is now commonly used on 16″ barrels. One reason the mid-length was used for the 16″ barrel is because the length from gas port to muzzle is the same as on a 14.5″ barrel with carbine gas system (with a 7.5″ gas tube) and on a 20″ barrel with rifle gas system (with a 13″ gas tube). This makes the dwell time about the same. Another reason is that on a 16″ barrel with carbine gas, you can’t mount a bayonet unless you have a custom extended bayonet handle or a second bayonet lug mounted on the barrel forward of the front sight tower.

      After all that, a 14.5 barrel with a mid-length gas system still gives you slightly slower bolt cycle saving wear and tear on the bolt carrier group, a longer sight radius with fixed front sight compared to a 14.5 barrel with carbine gas system and having a barrel that in the end after welding on the muzzle device is 16″ instead of 17″ – 17.5″. Obviously the disadvantage being that changing out the muzzle device requires more work.

    • Manny, great comment! Couldn’t have said it better myself!! Sums up exactly why we selected the 14.5″ barrel for this build, shortest possible without going to a carbine-length gas tube.

    • Thanks for the explanation. I do not currently intend to add a compensator with a 16″ mid-length. So we both end up with 16″ physical length, I might get a theoretically 50-100fps faster bullet (which is useless in practice), but I didn’t have to dork around with a gunsmith welding a compensator.

      More questions raised:

      Can I have a 14.5″ barrel and/or complete upper mailed directly to my residence, or is that in itself an NFA item?

      What effect would a buffer have on bolt carrier group wear and tear? I’ve heard good things about spikes tactical buffers with the powdered (tungsten?) rather than solid weights.

    • Sean, no restrictions at all on purchasing any length upper, it’s subject to the NFA once it’s mated with a lower. Only then does it become illegal if you don’t follow the rules. Buffers can get tricky and there’s lots out there to choose from. Stick with an H buffer as a baseline and you’ll be good. We may do a write-up on different buffers at some point too.

    • JD

      Hi Bryan-

      Note: I am not a lawyer, and nothing I say should be construed or interpreted as legal advice.

      I love your site and the info you share with us, and I appreciate it greatly.

      However, on this very site it states:

      “This is critical: you must receive approval before acquiring a weapon component that falls under the classification of the National Firearms Act. You can purchase a barrel shorter than sixteen inches without it being considered an NFA item but the muzzle break must be permanently attached, and the total length of the barrel and muzzle break combined must be at least 16 inches. Ownership of NFA items (even if unassembled), without an approved form, can be interpreted as ability or intent to construct an NFA weapon; you are then subject to prosecution and fines.”


      In my personal opinion, unless you buy the upper pre-assembled as a 14.5 barrel with the appropriate (and permanently attached) muzzle device, you may be taking a risk that involves huge consequences.

      I’m not trying to be a jerk or a troll, I really really like this site and I love the fact that you’re greatly expanded the DIY AR build, to include videos and a huge amount of documented info. I just want to make sure that no one comes to grief. I love the idea of a 14.5 middy barrel (especially from Bravo) but unless and until it is legal before it ever reaches my door (either because I have the NFA stuff squared away beforehand, or because it’s pinned and welded) I will happily make do with a 16″ middy for my own peace of mind.

  • Adam

    Bryan just wondering why you chose to go with a fixed front sight base rather than a low profile gas block and a rail mounted front sight?

    • Adam, we did that mainly to show how to install one, since throwing a flip up front sight on a rail isn’t a big deal. Also a low profile gas block is essentially the same installation as a FSB. the gas tube installs the same and dealing with the taper pins is something we wanted to show. Thanks for the question!

  • button

    The post befor yours should cleat things up.
    “no restrictions at all on purchasing any length upper, it’s subject to the NFA once it’s mated with a lower. Only then does it become illegal if you don’t follow the rules.”

    You can have a 1 inch barrel on an upper if you want! That upper isnt a weapon. Once you put it on the lower receiver your in trouble. Unless of course you use a 15 inch muzzle break!!

  • Slag

    What about using a pigtail gas tube? It is longer than the standard tube & is available in 3 lengths: pistol, carbine & rifle. I’ve seen it avail @ Brownells. according to theirs & others the increased length helps as you described slowing down the cycle rate. Has anyone used this product?

  • Pat

    Hi all. This series is very informative. I plan to use it to build my own AR very soon. I am new, so I am wondering how everyone would rate the quality of this upper. It seems like it would be a very good one. Would there be anything that one would want to consider to change? I plan on using a palmetto state armory lower kit with a Geissele Trigger Assembly to substitute the one used here.

  • Michael

    Hey just wanted to mention that Autozone has torque wrenches that they will loan you for like a$100 deposit, that they refund when you bring it back. So if you don’t have a buddy with a torque wrench Autozone will loan you a Torque wrench.

  • Golf5316

    Can I simply substitute a Daniel Defense 16″ barrel and dispense with the pinning?

  • Golf5316

    Can I simply substitute a Daniel Defense 16″ barrel and dispense with the pinning?

  • Chris in KY

    @Sean Lets you get 16 inches with flash hider saving about 1.5 inches in over all length.

    Important if you get in out of vehicles with it or have to use in confined spaces or just want or need a more compact weapon with out a tax stamp or travel restriction.

    You could just use a thread protector on a 16 barrel for same length but you get all of the muzzle blast.

  • CanyonVR

    Couple Quick Questions….

    “With our 14.5″ barrel you’ll also need to get a gunsmith to permanantely
    affix the BattleComp 1.5 that we’re using in this build to satisfy the
    requirements of the National Firearms Act.”

    I understand adding the 1.5″ to get the total length to 16″, but why does it have to be done by a gunsmith?

    AND…What exactly does it mean to “permanently” affix it on?
    …crush washer and fastened on?
    …crush washer, Loctite, and fastened on?
    …welded in place?

    • Rob Henderson

      Hey Canyon,

      Good questions! The BATFE covers this in their NFA Handbook and you can check out the chapter that references permanent attachment here. (

      The important text is the following: “Permanent methods of attachment include full-fusion gas or electric steel-seam welding, high-temperature (1100°F) silver soldering, or blind pinning with the pin head welded over.”

      It doesn’t necessarily have to be done by a gunsmith but it does need to be welded or high temperature soldered on, which many people don’t have the tools for. Most gunsmiths have the tools on hand to do this procedure so that’s why we mentioned a gunsmith.

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