How to Build an Affordable AR-15 Rifle: DIY Step-By-Step

Using parts from Bear Creek Arsenal, author Michelle Hamilton walks us through assembling an AR-15 rifle.

March 18, 2024 By Michelle Hamilton

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The AR pattern rifle, colloquially known as the “AR-15.” Everybody and their brother makes this style rifle, and even more people “build” or assemble their rifle themselves. At this point in time, it seems almost a sport in and of itself to do so. There seems to be a strong divide among builders, be it those who wish to build the “cheapest,” the most “boutique” (of which I am guilty), the most expensive or even those who build a specialty rifle geared for a singular purpose (such as a rifle tailored specifically for suppressor use). With all the parts available, is there a rifle for everyone? An even better question, is there really a wrong answer to the AR question? I jumped at the opportunity to write about building an affordable AR style rifle. The parts came directly from Bear Creek Arsenal, which admittedly has a spotty record for quality control and even a past scandal. Being typically an AR specifications snob, I was quite excited to dig into not only the specifications, but also the tolerances and QC with this new rifle build. At this point, the rifle will be built to factory specifications, using general build practices and all factory components. Later down the road, we will be “accurizing” this rifle on a budget and seeing just how much accuracy we can squeeze from this Bear Creek Arsenal AR.

Unboxing and initial opinion

My experience with Bear Creek Arsenal (BCA) has been quite limited through the years. Straight out of the gate, as I examined parts there was a lot of head nodding in approval and the occasional “hmm, not bad.” For a budget-minded rifle, the finish work was quite nice overall. All small parts came nicely packaged and separated. I like this, as anyone who is remotely obsessive about order will as well. Some parts weren’t quite packaged as well, which could result in finish damage, but none arrived as such. Overall, I am pretty impressed. I contacted BCA about product specs and they were slightly vague, but their barrels are 4150 CM-V and 416 Stainless.

Assembly practices lower receiver

bear-creek-ar15-build-how-to-02 — When building, be sure to use all proper tools and be sure to headspace all barrels, regardless of manufacturer. That box of parts becomes a functioning rifle. Make sure it functions properly.

Lowers go together fairly easily, but proper tools will make the AR life much easier. There are a few important steps to keep in mind. Make sure that not only is the castle nut properly torqued to 40 foot-pounds, but also make sure to stake the end plate to the castle nut. This displaces metal into the appropriate notch on the castle nut. Not only is this proper specifications and per Technical Data Package (TDP), but it is ultimately a fail-safe to keep the castle nut from loosening during use. Some people choose to skip this and simply use Loctite, thread locker or some other anaerobic thread locking compound. Do not do this. The buffer tube houses springs and moving parts, which the thread locking compound can interfere with (if too much is applied). This includes, largely, the buffer retainer pin and spring.

Use lots of lubricant or even grease. I like using Machine Gunners lube from Springco on most parts, with the exception of the trigger components. I do like to use a Molybdenum Disulfide grease (commonly known as Aeroshell 33MS or its more modern replacement, Aeroshell 64). This is good for initially fitting new parts, and it won’t damage parts in the initial mating process, one of which is the J-spring located in the hammer. Some social media “experts” may disagree, but this is preventative maintenance, reduces excess wear and any moving mechanical part requires lubrication. I like a small amount of grease on the pivot pin (also known as the “front takedown pin”). This makes installation of the pivot pin much easier. It also helps mate the components together smoothly.

All springs and detents need a light coat of oil upon initial installation, as do pins. I do like to add a small amount of blue loctite to the grip screw as well. Be sure not to over tighten the grip screw upon installation, as typically grips screws are made from steel and can damage the aluminum threads. When installing a factory/mil-spec trigger guard, take the roll pin, using sandpaper to slightly bevel the end which enters the lower receiver. This will not only remove small manufacturing burrs, but also slightly bevel the end, making it much easier to install. When doing so, be sure to use a lot of lubrication here. This will not only help with installation, but also coat the steel roll pin, reducing the possibility of corrosion or rust.

bear-creek-ar15-build-how-to-03 — Lowers are fairly simple, but the upper is where the magic happens. Shown here is the complete lower, although I swapped out the carbine weight buffer for an H2 (due to gassing of the upper).

Fully support the “ears” of the lower receiver, as these are weak points and are easily broken, especially if proper tools and steps are not taken or used. While polymer tools do exist for ease of installation, it is as simple as ensuring that the ears are fully supported in one fashion or another. Using a roll pin starter punch will allow for positive and level entry, once inserted to an acceptable depth (do not allow the starter punch to come in contact with the lower), with a brass gunsmithing hammer, a proper sized roll pin punch will easily seat it to proper depth. Come back with Birchwood Casey Perma-Blue and touch up any areas which may need it after installation.

Assembly practices upper receiver

The lower is pretty straight forward, but the upper receiver is where the “magic happens” so to speak. This is the component that contains a 55,000-58,500 psi (pounds per square inch) fiery reaction, the component that largely determines the accuracy of the rifle and the component that determines the reliability and function of the rifle as well. This is largely where “building” a rifle and “assembling” a rifle differs (in my opinion). As stated before, this will be covering basic assembly and we will be touching on accurizing and trueing the rifle for accuracy at a later date. This will not only give a good basis for comparison, but also show the importance of these further steps for those wanting to squeeze “the most” from their rifle. Before any work is initiated on the upper receiver, be sure to secure the upper receiver in an applicable vice block or similar tool. I do not like clamshell upper receiver blocks and have a preference to the old DPMS Panther Claw, JP Enterprises vice block, Geissele Reaction Rod and XS’s new upper/lower vice block (especially for upper lapping). The Panther Claw fully supports the upper receiver, works well for most applications and is overall my personal favorite.

When installing the barrel, if it fits snugly, great! That said, there are some uppers and barrel extensions that will require thermal manipulation to install. This is in fact, even better. Using direct heat (my preferred methods are by using a heat gun) to the frontal portion of the upper where the barrel is installed, heat until the barrel extension will freely (yet snugly) fit into the upper. What is happening here, is aluminum alloy expands and contracts much quicker and at different temperatures than steel (which is why I dislike aluminum and titanium alloy gas blocks). The aluminum will expand a couple thousandths of an inch, leading to acceptance of the barrel. Once the upper cools, the receiver practically closes and seals itself to the barrel. This lends to better accuracy and known by JP Enterprises as “Thermal Fitting”. This process absolutely requires proper tools and proper techniques. If a person does not have the proper tools, it is suggested that a qualified gunsmith fit the barrel for them.

Before firing, it is recommended to disassemble the bolt carrier group, by pulling the ejector and extractor (along with springs) and headspacing the bolt to the barrel. This is suggested on any virgin bolt and barrel, as while CNC machines are precise and while unlikely problematic, they are a tool, they are produced by human beings and as stated before, contains a violent and fiery 50,000-58,500 PSI reaction. Never let anyone tell you that checking a barrel and bolt combination with a “Go” and “No Go” gauge isn’t necessary. For those who shoot a lot, a “Field” gauge would be another handy tool to have as well. While many brands of gauges exist, I prefer Forster or Pacific Tool and Gauge (PTG for short) and the gauge brands I use.

For the typical assembly of a rifle pin gauging and mic’ing the gas port isn’t “necessary”, but it will tell the user a lot about how the rifle will be gassed and will perform. Remember, the traditional AR pattern rifle is a “gas impingement” (quoted from L. James Sullivan) rifle and feeding the rifle too much or too little gas will result in a failing rifle or a rifle that will not perform efficiently. For example, the proper gas port size for a mid-length gassed barrel will be 0.078-0.080 inch, anything outside of this spec will feed the rifle either too little or too much gas.

When installing the barrel nut, it is suggested to use either nickel based anti-seize or Molybdenum Disulfide grease such as Aeroshell 33MS or its newer replacement, Aeroshell 64 and a little bit goes a long way! For those using nickel bases anti-seize, it is easy to go from looking normal, to looking like the Tinman. This will allow the removal of the barrel nut later down the road for barrel replacements and will act as an anti-seize against heating and cooling, while also preventing galling of the mated surfaces. Be sure to follow all manufacturers torque specifications. While mil-spec barrel nuts torque spec varies wildly from 30-80 foot pounds, not all barrel nuts are created equal or even from the same materials. My personal favorite practice stems from Mega Arms manufacturing specifications, that is to tighten the barrel nut to half spec, then, loosen, then tighten to ¾ spec then full torque value. This helps mate the threads of the upper and barrel nut together (according to Mega).

Installation of the gas tube into the gas block is where a small roll pin starter punch and roll pin punch earns their weight. This tiny roll pin is not only easily lost, but can be damaged if using vice grips for installation. The roll pin starter punch allows for the user to apply adequate lubricant to the surface and also lightly sand out any manufacturing burrs left on the pin. Installation is straightforward and quite easy, but installation of the gas block to the barrel can be tricky, especially for non-dimpled barrels or new builders. For starters, if the barrel isn’t dimpled, dimple it! While Bear Creek Arsenal already completed this task, many manufacturers do not. This slight removal of material from the bottom of the gas block journal will help secure and keep a low-profile gas block in place and keep it from being knocked out of place from sudden bumps and bangs against it. The reason being, the set screws of the gas block mate with the indentation of the barrel, making the gas block much harder to knock loose than simply applying torque values to a completely rounded, non-dimpled barrel.

bear-creek-ar15-build-how-to-05 — Be sure to always stake your castle nut and torque to proper specs. Shortly after this photo was taken, I did replace this castle nut, as the BCA nut is not able to be staked.

Many may ask, why is this so important? As stated before, this is a “gas impingement” rifle and any disruption in the flow of gas will negatively affect reliability of the rifle and yes, is absolutely important for defensive use rifles. When torquing, do not over tighten! This is easily done, as the set screws are small and can strip out if not careful. I do suggest a small amount of thread locker or Loctite on the set screws as well. One of the neatest tricks to see if the gas block is properly aligned, along with the gas tube is to pull the bolt from the carrier, then, without the charging handle in the upper, slide the carrier in and out of locked position. If any resistance is felt, the gas key is rubbing the gas tube, meaning the gas tube isn’t properly fed through the barrel nut or the gas block isn’t properly aligned. It should be a smooth, effortless and resistance free movement. Best results are achieved by flipping the barreled upper upside down, on a flat surface (work bench is fine) and using the index finger to move the carrier in and out of place.

When attaching a muzzle device, there are various ways of proper installation or “timing” the device to the rifle. The most common installation method of flash suppressors will use what is called a “crush washer” or “peel washer”. Both work at effectively keeping the flash hider installed and in correct time, but when installing compensators or muzzle brakes, I do prefer shims as this allows for more precise timing of muzzle devices. When installing muzzle devices with shims, I would recommend using Rockset over a Loctite or thread locker. When installing, again, be sure to follow all manufacturer recommendations. All parts assembled well, with no problems whatsoever. Everything was smooth, worked well and I was quite pleased with Bear Creek Arsenal’s parts. They definitely offer the user a lot for their money and an overall decent product with a decent finish. With the rifle assembled, headspaced, and a pre-range function test of action, trigger and safety it was time to get it out on the range. The rifle was ran for reliability and accuracy both, using a mixture of bulk NATO FMJ, Defensive Hollow Point, Soft Point and Solid Copper options, along with Match Boat Tail Hollow Point. For optics, an Aimpoint Comp red dot and Nightforce SHV 3-10x42mm with MOA reticle were used. All accuracy tests were performed at 100 yards, with 5-round groups shot.

bear-creek-ar15-build-how-to-06 — Always use anti seize or a Molybdenum Disulfide grease such as Aeroshell 33MS or 64 on the barrel nut thread. This prevents galling and the upper seizing up due to repeated heating and cooling.

With standard bulk NATO 5.56mm 55-grain M193 and 62-grain M855 (Turkish SS109 from ZQI) the rifle shot respectful 2.25-2.5 inch groups at 100 yards average and shot a pretty respectful .95-1.25 inch groups with SIG Sauer Match 77-grain BTHP (Boat Tail Hollow Point) Match ammunition. Function testing went well and there were no accelerated wear patterns on any components (which seems to be a trending social media rumor with BCA components). The carbine proved 100% reliable with the ammunition used and ate the 350 rounds with no problems. I did note that the finish on the barrel, while uniform is exceedingly thin and scratched fairly easily, especially when installing the gas block.

Final Thoughts

bear-creek-ar15-build-how-to-07 — The finish and anodizing on BCA’s component is very good and better than expected.

All in all, I’m pretty happy with the results from Bear Creek Arsenal’s components. As far as a budget friendly option, they did quite well overall in fit, form and finish. The biggest complaint was, the M4 barrel supplied with this kit was quite over-gassed. Luckily however, a Velocity Arms adjustable gas block was a quick solution to this issue. Make no mistake though, I do not like “solving” an over-gassing issue with adjustable gas blocks, nor do I like using the “band-aid” of heavier buffers as a solution either. Due to this, the likelihood this carbine will ever see a suppressor is quite slim. If one listens strictly to internet lore, they would expect an absolute train wreck and at first, so was I. But the experiences differ substantially from that. Assembly went smooth overall, with little to no issues (the roll pins had burrs and internal parts were dry/no lubrication, which are easy fixes). Bear Creek Arsenal’s finish really impressed, their anodizing looks good. Fit and finish quality I would rate fairly good overall. I would like to know more about their lower parts and their Q.C., but for the price point BCA offers, I can work with it for what it is. For what they offer and the price point they offer it, Bear Creek Arsenal did a good job. Do they offer the highest end rifle on the market? No, they don’t. Will they compete with those same rifles? No, they won’t. Do they offer decent parts to build a decent budget rifle? Yes, they absolutely do. For a sub $500 rifle, with them often times demanding low to mid $300 range? They are more than adequate to fill that void.