AR15 Gas Block Options

AR15 Gas Block Options

9. Gas Block options are numerous.  The standard Front Sight Base (FSB) sometimes called Front Sight Post depending on manufacturer, was the original AR15 gas block. As hand guards changed and barrels became free float, the need for more variety of gas blocks became apparent.  The purpose of the gas block is to connect the gas tube to the barrel. The gas tube sends gas to the bolt carrier to operate the function of the action, to eject a round and load a new round from the magazine.

If considering the standard FSB, one should also understand the differences between the F marked FSB and the non F marked FSB. The F marked FSB is 0.040″ higher than the the non F marked FSB. The non F marked FSB is traditionally for A1 and A2 style uper receivers. The F marked front sight base is for use with flat top upper receivers.

Before selecting a gas block, some things you should know. What is the diameter of the barrel at the gas port.  This could vary from .625, .750 or even .863.  So the block should be matched to the barrel. If you intend to install a pinned gas block, ensure that the barrel is pre-drilled to receive the pins. Not all barrels are pre-drilled to receive the traditional FSP, therefore a pinned gas block won’t work and a clamp on style gas block will be necessary.  Will the gas block fit within the hand guard?  Will you want a rail for a front sight on the gas block? Most gas blocks are fixed position but there are also adjustable gas blocks, meaning that the amount of gas transferred into the gas system is constant on a fixed gas block, or it can be adjusted by the user to super tune the rifle system with an adjustable gas block.

 

AR15 Barrel Options & Definitions

AR15 Barrel Options & Definitions

8. The Barrel of the AR15 is one aspect of the entire platform that someone can obsess about for quite some time. And for good reason since the barrel is the final word on accuracy and reliability, and sometimes cost, of the entire AR15 build. With so many options like length, gas system, caliber, twist rates, gas system lengths, and each variable having pros and cons; the barrel is one area of the rifle that should not be neglected! Proper selection of the AR15 barrel can be a book onto its’ self.

One must weigh the pros and cons about all aspects of the barrel when making a decision.  For example talking about supreme accuracy with pistol length barrels may be a moot point. Accepting a slight loss of supreme accuracy, but still maintaining combat accuracy and reliability may be a good balance. The intended use of the AR15 should really dictate the type of barrel used.

A. AR15 Barrel Profile

Government Profile is thicker than the original Light Weight A1 style barrel. The M16 and M16A1 profiles were thin lightweight barrels with .625″ diameter at the gas block. The Government profile A2 barrel was made with a greater thickness from the gas block to the muzzle to resist flexing and to allow a longer period of sustained fire without overheating. The rest of the barrel was maintained at the original thickness to allow for the the M203 grenade launcher to be attached.

Featherweight
Lightweight, AKA Pencil, is the original profile barrel. It is .625″ diameter at the gas block.

Medium
Heavy
Bull
Proprietary  & Special Purpose

B. AR15 Barrel Materials vary.

Stainless Steel  barrels are generally considered to be the most accurate and are often preferred by bench rest and competitive shooters. They are also a great choice for hunters as there is less chance of corrosion due to weather.

Chrome Moly Vanadium (CMV) are steel barrels and can be considered the starting point for any AR15 barrel.  The name can be misleading, and these are not chrome lined barrels.  CMV barrels are the most affordable barrels on the market, but require the most maintenance to prevent rust or corrosion.  If you’re really good about cleaning your barrels religiously, this might be the right choice for you.

Chrome Lined barrels are considered to be the most durable of the AR15 barrels. This is because the additional chrome lining adds self lubrication and prevents wear.  The self lubrication also aids in extraction.  However the trade-off is a slight loss of accuracy. Chrome lined barrels are great for tactical, home defense, or hunters; but might not be the preferred choice of a bench rest shooter looking for supreme accuracy.  Just how much accuracy is lost?  It is generally accepted to be about .5 MOA when compared to stainless steel barrels.

C. Rifle Cutting (Rifling)

Rifle cutting, or rifling, can be button/cut or forged.  Cold Hammer Forged (CHM) barrels are considered to be more dense than cut rifled barrels. This is because of the forging process hammering the lands and grooves into the barrel, no material is removed. Whereas with a buttoned or cut rifle barrel, the lands and grooves are being cut, or reamed, into the barrel.

Buttoned or cut rifling is generally preferred for it’s accuracy. The forging process can introduce stress into the steel, and this stress is known to reduce accuracy.  For most shooters the accuracy loss is negligible, however for bench rest shooters that squeeze every .01% of accuracy out of every component, these CHF process might not be preferred.

D. Barrel Twist Rate

The twist rate of the barrel is the rate of turn the bullet will experience in a given distance.  For the purposes of this article only the 223 Remington /  5.56 NATO rounds will be discussed. The information provided will prove a point which can then be applied to any of the nearly countless AR15 chamberings.

First, the twist rate, or ratio, can be defined using “1:7” as an example. What this means is the bullet will experience one complete revolution within a 7” length.  Whereas a 1:9 twist rate means the bullet will experience a complete revolution within 9” of length. Which is right? They are both right depending on the needs of the user, and the intended ammunition to be shot from the barrel.

The higher the twist rate, meaning the lower the number of inches taken to complete a revolution, means the more stable the bullet will be leaving the muzzle of the barrel. However it is possible to over stabilize a bullet. For example shooting a 40 or 50 grain varmint round from a 1:7 barrel may cause the bullet to turn at such high revolutions per minute (RPM) that the copper jacket can actually be removed from the lead core.  This over stabilization can cause a major loss in accuracy and a loss in ballistic performance for hunting purposes. This is why it’s important to match the barrel to the ammunition, and visa versa.

When it comes down to it, any twist rate will shoot just about any bullet, but when discussing optimization the twist rate should be matched to the ammunition you intend to shoot.  The general rule of thumb used is that a 1:7 will shoot bullets in the 70 grain range the best, but will also shoot 60 grain bullets just fine and even most 50 grain bullets without any problems.  1:9 shoots varmint bullets in the 40 and 50 grain range the best, but will also shoot heavier bullets, though at longer distances the heavier bullets will become unstable and cause a loss of accuracy.  1:8 seems to be the modern trade off and is a twist rate gaining popularity. The 1:8 seems to shoot everything well.  So the barrel should be matched to the bullet, and if you are not sure; you usually can’t go wrong with a 1:8.

E. Barrel Length will affect many factors on the flight of the bullet including velocity and distance. All things being equal a longer rifle barrel will generally produce more accuracy at longer distances due to the increased velocity, than a shorter pistol barrel for example. It is also important to note that barrels shorter than the carbine length 16” are sometimes considered to be controlled items by the ATF and special permission is required. One must also check short barrel rifles (SBR) with their state, county and city as SBR’s are illegal in some areas.

14.5” barrels are controlled, therefore not owned by most civilians. Though a 14.5” barrel with a permanently attached long muzzle device will usually satisfy laws regard Short Barrel Rifles(SBR).  14.5” barrels are absolutely great for CQB or urban tactical and home defense (with the proper permission). The trade off is a loss of accuracy and terminal performance at longer distances.

16” barrels are the most popular allowing for the most flexibility within the rifle, especially because they do not require any special ATF permission slips. 16” barrels are seemingly good at everything,  home defense, three gun competition, most tactical situations, and will even reach out with combat accuracy and effective terminal ballistics to 300 yards or so.

18” barrels are gaining popularity.  These barrels are especially popular with three gun shooters. They are usually coupled with mid length or intermediate gas systems giving a great balance of distance, velocity, and reduced recoil impulse while maintaining a manageable weight.

20” barrels were used on the original M16 rifles (the grand father of the modern civilian AR15). The longer barrel will give you more velocity which will increase the effective range of the bullet.  Bench rest shooters may desire this increased accuracy thus opt for a longer barrel. However the added weight of the barrel may be a turn off for hunting or tactical purposes and may be clumsy for use in home defense or CQB.

F. AR15 Gas System Length

There are different length gas systems for use on the AR15. The gas system length is sometimes predetermined by barrel length. However in some circumstances different gas system lengths can be used.  For less recoil impulse it is preferred to use the longest gas system possible, with the least dwell but still leaving 5” or more of barrel length in front of the gas port (dwell).  For comparison purposes the M16 and M4 have dwell of 6.8” and 6.7” respectively.

Pistol length gas system…..

Carbine

Mid (Intermediate) – slower cyclic rate yield easier follow up shots, shorter dwell time means less pressure on the bolt carrier yielding less wear and tear and less perceived recoil. improved extraction.

Rifle

Extended

Piston

 

G. Gas Port Size is the hole in the barrel which allows gas to bleed off from the barrel, into the gas block, through the gas tube and into the upper receiver and bolt carrier. The size of the gas port is to be specified in conjunction with the gas system length and dwell. The gas port size is one means of tuning the rifle to specific ammunition.

The standard gas port size varies from .059”-.090” and the maximum would be .120” since that is the internal diameter of the standard gas tube. However a larger size gas port diameter can cause the AR15 gas system to become over gassed. The larger size gas ports are not recommended on shorter barrels, and anything over .090 is not usually recommended except with use on an adjustable gas system.

The two trains of thought on the subject; Smaller gas port hole with more dwell OR Larger gas port hole with less dwell.

Common gas port diameters based on barrel length…  Please note this chart doesn’t take into account other factors such as barrel diameter at the gas port, bolt carrier weight, buffer weight or buffer spring tension,  ammunition or suppressor use. These port sizes will also vary by manufacturer.

  • 11.5” barrel…..   .810”-.094”
  • 14” barrel…..      .059”-.086”
  • 16” barrel…..      .059”-086”
  • 20” barrel…..      .086”-.096”
  • 24” barrel…..      .089”

Barrels with a larger diameter at the gas port (.750” diameter) tend to lean towards the middle to larger hole size, while barrels with a small diameter (.625” diameter) at the gas port tend to lean towards the low to middle hole size. Gas port size is one thing that should be considered but shouldn’t be over-thought.  Most of the quality manufacturers have done the thinking for you, and unless you specifying a custom made barrel it might not be something necessary to consider too much. When in doubt err on the smaller side of port sizes, as the port size may be enlarged later if necessary.

H. Feed Ramps are available in two basic varieties, standard (aka Rifle) and M4 style feed ramps.  The purpose of the feed ramps is to aid the tip of the bullet into the barrel extension, and thus properly chambered. This improved chambering is especially noticeable with ammunition that is pointed at the tip, vs. rounded nose ammunition.  It is also important to note that the M4 style feed ramps are best utilized when paired with an upper receiver which also will have m4 feed-ramp extensions.  One should never pair a standard/rifle feed-ramped barrel extension with a upper receiver that has m4 feed-ramps.

 

AR15 Upper Receiver Options

AR15 Upper Receiver Options

7) The Upper Receiver Assembly is the Top half of the gun that consists of the barrel, bolt, hand guard, and other various parts necessary to operate the AR15 rifle.  This top half is highly customizable and changing the top half can change much of the characteristics of the firearm, even the caliber.

Like the lower receiver The upper receiver its’ self is available forged, billet or extruded. The same pros and cons that apply to the lower receiver in terms of manufacturing process also apply to the upper receiver.  For further information about these manufacturing processes, please read the section title “AR15 Lower Receiver Options”.

Some upper receivers will have a forward assist, though not all. The forward assist allows you to bump the bolt carrier group forward incase some minor dust, dirt or fouling is preventing a complete chambering of your ammunition. This is useful in critical situations such as military, law enforcement or home defense.

Most upper receivers will have a standard charging handle which resides above the receiver extension (buffer tube). However some upper receivers have the charging handle attached directly to the bolt carrier group, thus there will be a cut out in the upper receiver for this fixed charging handle.

Upper receivers are available with a “flat top” sometimes called an A3 or A4 style receiver. The flat top receiver, with machined picatinny rail is by far the most common. The A1 and A2 style upper receivers will have a built in carry handle and rear site. The type of site varies based on the A1 or A2 designation.  Some manufacturers, such as Rock River Arms, have proprietary uppers which incorporate flat top rails with built in sights.

The A3 style (Also called A4 by some manufacturers such as  Rock River Arms) flat top receiver allows for the mounting of iron sights or optics or both. The versatility of the picatinny rail is perhaps the number 1 reason for the popularity of the flat top upper receivers.

AR15 Lower Receiver Parts

AR15 Lower Receiver Parts

6 ) In addition to the trigger, butt stock, pistol grip; other AR15 Lower Receiver parts you will need to complete your lower receiver include: the magazine release button, the safety selector, and the bolt release.  You will also need various small springs detents and pins.  All of these parts will be available in an AR15 Lower Parts Kit (LPK). However upgraded after market, ambidextrous,  or enhanced parts including the magazine release button, safety selector, and bolt release are also available.

An Ambidextrous bolt release such as the Magpul B.A.D. lever will allow you to operate the bolt release with your trigger finger.   Ambidextrous magazine release allows you to drop the magazine using your offhand.   Other aftermarket parts allow you to truly customize the setup, feel, and utility of your AR15.

The Trigger assembly is included with most, but not all, lower parts kits.  Learn more about trigger assemblies for the AR15

AR15 Pistol Grip Options

AR15 Pistol Grip Options

5) Pistol Grips Give you something to hold onto, and are a necessary component of the AR15 rifle.  Pistol grips on your AR15 are really a matter of personal preference as some grips may vary in angle, girth, texture and shape.  What fits one hand may not fit another.

Some things to consider when comparing after market AR15 pistol grips…

Some grips vary in angle. Some grips vary in girth. Some grips have compartments inside for batteries or other storage.

Proprietary grips like the Monster Man Grip would be required in some areas to avoid “Assault Weapons Bans” (AWB’s).

Grip materials also vary, some grips are sticky rubber, while the Military Specification (Mil-Spec) grips are firm plastic with a partially textured surface. Some grips are aluminum and even others wood.  There are pros and cons to each material used to construct the grip such as grip-ability and weight.

Not much more can be said about grips other than to try a few and see what fits you the best.

AR15 Buffer Options

AR15 Buffer Assembly & AR15 Buffer Options

4) The Buffer Assembly is made up of a tube, spring and buffer. There are differences in the tube, but differences in buffers and springs will allow you to tweak or customize the AR15’s perceived recoil.

Selecting a buffer tube is fairly straight forward and often dictated by the butt stock you desire on your AR15.  Fixed stocks will typically use an A1 or A2 buffer tube.  Adjustable stocks will typically utilize a Commercial or Military style buffer tube.

“Buffer tubes” are actually known as receiver extensions, or receiver extension tubes.  A Milspec buffer tube is slightly smaller in diameter but it is forged aluminum, not extruded which makes it stronger even though it’s slightly smaller. Also there is a difference with how the threads are cut on the milspec versus commercial buffer tubes, making for a better thread lock or thread engagement, with the military size tube and the lower receiver.  It is important to note that though the forged buffer tube may be considered stronger and the thread engagement considered better with the military tube, there is not any evidence that this added strength is necessary in a civilian AR15. Under normal use situations, the commercial buffer tubes are more than adequate to do what is asked of them.

 

Other differences with the commercial and military buffer tubes include the commercial sized butt stock will have a loose fit on a military sized tube. A military sized butt stock likely will not fit on a commercial tube. A military style buffer tube usually will have less adjustments, only 4 versus the 6 adjustment points on a commercial buffer tube. Some manufacturers have systems that do not use either the milspec or the aftermarket tube size… The early Choate stock is one example of a proprietary tube.

 

Buffers are essentially engineered weights that help to slow down the cyclic rate of the bolt as it cycles in the upper receiver and the receiver tube.  Buffers are available in two basic sizes, Rifle or Carbine. This rifle or carbine size designation refers more to the buffer tube than it does to the barrel length.  Pistol sized buffers for the 9mm and the 45 may also vary in size and weight. Non-traditional hydraulic buffers are also available.

Carbine length buffers are available in varying weights. Standard Carbine is a tube with steel weights inside.  Two steel weights, plus one tungsten weight is considered a H1 (sometimes simply referred to as an H), 2 tungsten weights plus 1 steel is H2, and 3 tungsten is H3. Since Tungsten weighs more than Steel, the weights of the buffers will vary.  However the weight of the buffer is not the only factor to consider, as the segmentation of the individual weights can prove to provide less bolt bounce. H buffers seem to be the best starting point when in doubt on a carbine sized AR15 buffer, heavier weights may be required for shorter gas systems.

Weights may vary from the chart below, but the chart is provided as a comparison tool to show the differences between the different buffers.

Standard CAR…..              2.9 oz.
H buffer is …..                    3.8 oz.
H2 buffer is…..                   4.6 oz.
Rifle buffer is…..               5.17 oz.
9mm buffer is…..              5.5 oz.
H3 buffer is…..                   5.6 oz.

Which is right, heavier or lighter buffers and springs.  It all comes down to shooter style and preference.  Generally speaking a heavier buffer will slow down the cyclic rate more and have less felt recoil on the shooter. Where as a lighter buffer will have a faster cyclic rate allowing for quicker follow up shots.  However there is more to it than that, such as gas system length, and pressures from the ammunition so some experimentation may be necessary.

Like buffers, the buffer springs too are available in varying degrees of resistance to the backwards force of the Bolt.  The first importance is to ensure your spring is matched to the size of your buffer tube (rifle length or carbine length tube). A rifle length buffer spring is approximately 12” long +- ¾”, and a carbine length spring is approximately 10 ¾” +- ¾”.  After determining your proper spring length, you must determine which spring resistance is right for you.

There are springs on the market which have increased or reduced resistance to the bolts rearward movement when compared to a standard military specification spring.  Mixing and matching spring tension with buffer weight will have different effects on your AR15. It is generally suggested to start with a standard buffer spring.

 

AR15 Butt Stock Options

AR15 Butt Stock Options

3. The Butt Stock Assembly,

The Butt stock assembly is made up of basically a buffer tube (actually known as the receiver extension tube), and a butt stock, which attach to the lower receiver. Within the tube, will reside the buffer and buffer spring.  Butt Stock Assemblies come in two basic varieties, fixed and adjustable. Before selecting a butt stock one must familiarize themselves with the laws of their area, as adjustable butt stocks are not allowed in some states, counties or cities.

 

A fixed butt stock is simple and straight forward, it doesn’t move and does not adjust. Though there are multiple styles available. Fixed butt stocks are available skeletonized or like the traditional A1 or A2 style butt stock you see on M16 service rifles.  Weights are even available for bench rest shooters to insert into their stock.

Adjustable butt stocks are increasingly more common because they adjust to the size of the shooter, often times in more ways than one.  The most basic M4 Adjustable butt stock adjusts for length of pull.  Some more complex butt stocks allow the shooter to adjust for comb height as well.

Before selecting a butt stock, be sure to read on about Military Vs. Commercial Buffer Tubes.

Understand how Buffer Weights effect your AR15.

 

 

AR15 Trigger Assembly Options

AR15 Trigger Assembly Options

2. Trigger Assembly

The trigger is a critical assembly of any firearm, without it the gun won’t go bang! But there are different triggers for different applications.  There are numerous triggers on the market including single stage, two stage and drop in. Picking the right one is critical to a safe and reliable AR15.

A. Before selecting a trigger for your AR15 you should be familiar with some terms and characteristics of any trigger assembly. Knowing the following terms will allow you to better understand which trigger is right for your application.  First, the trigger assembly is actually known as the fire control group.  Slack, sometimes called take-up, is rearward movement of the trigger before the trigger engages the sear. Creep is after the sear has been engaged, any further/additional rearward movement of the trigger before the hammer falls. Over travel is how far the trigger can continue to travel rearward after the shot breaks.  Trigger pull weight is the amount of force it takes to pull the trigger, engage the sear, and cause the hammer to drop.   A higher trigger pull weight, of 7-9 Lbs., is usually preferred for tactical or home defense triggers, while a lighter trigger pull weight 3-5 Lbs. is usually preferred for precision or competition purposes.

B. A single stage trigger requires one trigger pull. Meaning the single stage trigger has little-to-no movement (slack or creep) in it before the sear is tripped. A standard US Government Issue M4 or M16 riles have a single action, and most out of the box civilian AR15’s will come with single action triggers. Most AR15 Lower Parts Kits (LPK’s) will have single action triggers unless otherwise noted.

C. Two stage triggers, while requiring only one trigger pull, is broken between two stages. The first stage will have some take up with a higher pull weight. There will be a slight disconnect, therefore it will often be very noticeable when the first stage ends and the second stage begins.  The second stage of the two stage trigger will require much less pull weight.  For example the first stage may require 5 Lbs. of pull and the 2nd stage only 2 Lbs. The advantage of a 2-stage trigger is that with proper training when you pull through the first stage and get to the hold on the second stage, you know you’re right on the edge of it breaking.

D. A drop in trigger kit can be single stage or two stage.  The drop in triggers come pre-assembled and are great for the do it yourself AR15 builder or professional gunsmith alike.   Many, though not all, drop in triggers are adjustable which allows you to customize your trigger to perfectly suite your needs.

E. Generally speaking, all things considered equal, a single stage trigger is usually preferred for high stress situations such as tactical or home defense.  Single Stage Triggers are also often preferred in rapid fire such as a three gun type competition.  Two Stage triggers are often preferred for bench rest or target shooting or service rifle type competitions, they are often considered more accurate.  Triggers are one of those components in the AR15 that people can obsess about, but it really comes down to shooter preferences and familiarity with one’s own trigger.

 

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AR15 Lower Receiver Options

1. The AR15 Lower Receiver Options

The stripped Lower Receiver IS the firearm. This is the part that has the serial number, everything else attached to the lower receiver are just parts. Lower receivers are available in a variety of types.

 

A. A “Forged” lower receiver refers to the process of forming a block of aluminum by pressing  raw metal into its almost final shape. Much of the detail is outside detail is pressed onto the forgings, which are then machined to the specification with cut outs and holes etc…  Forgings are the most common lower receivers, and can be considered the standard, on the market because they tend to be the strongest and nearly the cheapest to manufacture.

B. A “Cast” lower receiver is the process of pouring liquid metal into a shape.  Though casting is possible there are not many manufacturers using this process to make lower receivers.   After casting, the receivers are then machined.  Cast receivers are considered to be weaker than the standard forged receiver.  Cast lower receivers can typically be identified by the raised lettering and a rougher appearance within the mag well.

C. “Extruded” Lower receivers are not very common. Extrusion is the process of forcing heated aluminum through a shape . The Extruded lower receiver is then cut and machined to specification.  It is then cut to length and final machined to final configuration. Extruded Lower Receivers tend to have less detail and shape than other receiver types.

D. “Billet” Lower Receivers are the 2nd most common fabrication method used for fabricating lower receivers today.  A billet lower receiver starts as a block of aluminum which is then completely machined and shaped to the final shape and specification.   This type of receiver is generally referred to as a “billet” receiver because the block of metal is what is known as a billet.  Billet lower receivers tend to require the most investment because of the extensive machine time necessary in fabrication of the part.  Billet Lower receivers typically are of the highest tolerance due to the total machining process but are not always completely “mil spec” because of some size variations.

E. A newer lower receiver to enter the market in recent years is the polymer lower receiver. Polymer lower receivers are the cheapest to make because plastic is cheaper than aluminum and the molding process is quick and fairly accurate allowing the manufacturer to form almost all of the detail into the raw part.  However polymer lower receivers tend to be the weakest of all the lower receivers on the market.  Some manufacturers are attempting to overcome the weakness of the material by utilizing metal inserts in the critical high-stress areas.  Polymer is also more prone to size fluctuations due to temperature differences than aluminum.  This may cause some “fit” issues.

F. Which is a better lower receiver? The general consensus is that a forged 7075 aluminum lower receiver is certainly the most common and perhaps the best on the market when made to meet or exceed military specification (mil spec).  7075 Aluminum is much tougher then 6061 aluminum. 6061 Aluminum is lighter, and often referred to as air craft grade aluminum.

Billet, though technically weaker than forging, are very popular because they tend to be the most pleasing in appearance and any weakness deficiencies can be designed out by adding more material where necessary. Cast is generally not preferred due to the rough appearance, and the weakness incurred during the manufacturing process.  Polymer lowers are not yet time proven and are still an experiment as the bugs are worked out of the designs.

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AR15 Design & Build Guide – Table of Contents

AR15 Design & Build Guide.

 

While there are numerous guides for the assembly of the AR15 rifle, there are few that will explain what the differences between the parts are.  The AR15 is a highly customizable platform. A rifle can be built highly specialized for a specific task or mission. Some of these tasks would include citizen home defense, competitive shooting, hunting, LEO, Personal Defense Weapon (PDW), Military Close Quarter Battle (CQB), Military precision, bench rest shooting and on and on and on…  While one build may work O.K. across the board, you wouldn’t necessarily want a long heavy bench rest shooter on a hunting trip or for home defense, and you wouldn’t necessarily want a Military CQB model for hunting or bench rest shooting.  So, this guide will help lead you through the process for selecting each part in building your own or specifying parts for your gunsmith to build YOUR new custom AR15!

Upper Receiver & Lower Receiver.  These are the two basic assemblies of the AR15 platform of rifles.  There are sub-assemblies for each the upper and the lower.  Below is a table of contents,

 Lower Receiver

  1. The Lower Receiver
    1. Forged
    2. Casting
    3. Billet
    4. Polymer
    5. Comparison
  2. Trigger Assembly
    1. Definitions of trigger terms (creep, weight, over travel)
    2. Single Stage Triggers
    3. 2-stage Trigger
    4. Drop in trigger kits
    5. Comparison
  3. Butt Stock Assembly
    1. Stocks – fixed, adjustable,
    2. Tubes – commercial, military
  4. Buffer Assembly
    1. Buffers
    2. Springs
  5. Pistol grips
  6. Other AR15 Lower Parts (pins, springs, detents, mag release, safety selector)

    Upper Receiver

  7. The AR15 Upper Receiver (Forged, Billet)
  8. AR15 Barrels
    1. Barrel Profile
    2. Barrel Material
    3. Rifle Cutting
    4. Barrel Twist Rate
    5. Barrel Length
    6. Gas System Length
    7. Gas port size
    8. Feed Ramps
  9. Gas Blocks
  10. Gas Operating Systems
  11. Muzzle Attachments (compensator, flash hider, crowned)
  12. Bolt Carrier Groups
    1. Weight
    2. Coating
  13. Hand Guards (hand guards, free float, rails)
  14. AR 15 Sights
  15. Other AR15 Upper Parts (charging handle, forward assist, dust cover, delta ring, barrel nut)

    General Information

  16. Some Basic AR15 Design Ideas & Considerations
  17. Understanding different coatings and metal treatments.
  18. Definitions, Acronyms, and Abbreviations.
  19. AR15 Failures and trouble shooting.
  20. History of the AR15 and predecessors.
  21. Legal Concepts & the AR15