I want to start an image gallery of YOUR AR builds at home… send in some pics and I’ll start to post them over here:  http://www.ar15fornoobs.com/build-gallery/

Send to: info [at] ar15fornoobs (dot) com

In short, it works!!!  I’ve had the AR out to the range about 3 times now… I just shot a quick video of it functioning this weekend:

http://www.youtube.com/watch?v=q8wWA-Gyqok

Pictured above is the bottom side of my new Yankee Hill Machine upper that showed up in the mail.  This one came with all the parts needed to assemble the Dust Cover, and Forward Assist.  Reference the Upper Detail post if you’re not sure what those are.  This upper does have T-Marks and M4 style feed ramps (pictured below).  I’ve got a whole post dedicated to M4 Feed Ramps to shed light on what those are for and if you need them.

1. Reference to the specific M4 model / configuration of an AR-15 produced by Colt. This is a Colt model number and is NOT available to civilians. (Sad Trombone)
2. The type of feed ramps cut into the upper receiver and barrel.  This post is dedicated to that concept.

Both upper receivers and barrels are available in an ‘M4′ design. What exactly is that?  Here’s what I can gather:  [click this post to expand the article]

Your barrel extension (the part that fits in your Upper Receiver)  already has feed ramps built into it.  When the bolt pushes a new round towards the chamber, the bullet tip hits the feed ramp and gets guided into the chamber. Pretty simple.

M4 Feed Ramps take the standard feed ramps to the next level . M4 style ramps extend beyond the end of your barrel extension, and continue this deeper cut through your upper receiver.  By extended the feed ramps even further, you can help eliminate possible feeding problems.

How so?  Lets say the spring in your magazine is going bad, and after you fire a chambered round, the new round in the magazine hasn’t quite made it all the way to the absolute top of the magazine before being slammed forward by the bolt.  Or, maybe the round is faulty and the bullet projectile is not centered.  It is possible a non-M4 design might jam, where the M4 feed ramp would catch the tip of your bullet, and help guide it into the chamber.  Yes, another example in your life where ‘just the tip’ helps you survive.

So do I need M4 feed ramps???  Honestly, nope.

A lot of AR15 components come with M4 feed ramps as a standard.  BUT, you do need to pay attention to the parts that you’re ordering.  Your Upper and your Barrel Extension SHOULD match.  They don’t HAVE to, I’ll explain.  Below is a diagram courtesy of ar15barrels.com.

Lets talk about the lower left corner of the diagram.  If you pay ZERO attention to what you’re buying / assembling, there’s a 25% chance you’ll configure a pretty dumb idea.  What’s happened in this scenario is that a NON-M4 barrel is installed into an M4 Upper Receiver.  If a round starts to feed and hits the M4 ramp on the Upper, it will MOST CERTAINLY jam when it its the lip of the barrel extension.  Don’t set yourself up for disaster, avoid this configuration.

Videos I watched that showed step by step instructions on how to assemble the entire upper:

With each variable below… I’ll also explain what aspect of your barrel it affects.  Before going through this list… keep in mind what type of AR you’re going to build.  A short, tactical close range AR?  Maybe a long range hunting rifle, or varmit eliminator?  Multi-purpose zombie killer?  Your overall goal should be what drives your decision making when picking barrel attributes.  Here we go:

Length – Barrel length affects accuracy and muzzle velocity of your bullet.  The longer the the barrel, the more accurate your rifle will be at long range.  Your projectile will also travel a further distance in the barrel with extremely high pressure behind it allowing it to accelerate faster.  On the flipside, a shorter barrel is lighter, and easier to maneuver in confined areas.  If you’re clearing a home or in an urban setting defending your life / family… you might not want to be swinging around a heavy and long barrel.  With 16″ being the most common, I saw AR-15 barrel lengths range from 7″ to 24″ with various stops in-between.  The barrel length will affect your Hand-Guard lenth, and gas tube length, so be conscious of that when ordering additional parts.

Twist – The  rifling inside your barrel act on the bullet to cause a spinning gyroscopic affect on it.  The barrel twist is expressed in a ratio, like 1:7 or 1:9.  The ratio refers to the number of inches it takes for the bullet to make a full 360 degree turn.  So a 1 turn in 7 inches twist spins the bullet faster than 1 turn in 9 inches.  The faster you spin your bullet, the more stable it should be when traveling through the air… but there’s a catch, you can OVER spin light bullets causing inaccuracy and drift (bad).  So keeping things simple,  you choose the barrel twist based on the weight of the bullet you plan to shoot.  Bullets from 35 to 50 grains in weight  should be used with a twist of 1:14 – 1:12.  1:9 (most common) and 1:10 are suitable for 45 to about 70 grains.  The most common weighted bullet I’ve seen is 55 grain.  The military steel core ammo I saw for combat was 62 grain.  1:9 twist seems to be the winner as ‘most likely compatible’.  For 69 to 90 grain bullets, a twist rate of 1:8 or 1:7 should be used.  Not sure what type of ammo you’ll be using?  Take a look online at some ammo stores and maybe you’ll see some common weights and pricing like I did.

Chrome Lining – There is much debate over this topic, and apparently a lot of myths… so I’ll keep this one simple.  Chrome lined barrels offer easier cleaning, higher resistance to corrosion, and higher resistance to super hot temperatures experienced during rapid fire.  The US military used chrome lined barrels, but it isn’t necessary for civilian use at the range.  It is said that a chrome lined barrel is less accurate, but the CDT blog stated the difference being about 1/4″ at 100 yards.  Your budget may play more of a role in this decision, as chrome lined barrels are significantly more expensive than non-chrome lined ones.  I may stick with the basic barrel for my build, but I need to check out the pricing differences first.

Twist Source: http://cheaperthandirt.com/blog/?p=2625
Chroming Source: http://cheaperthandirt.com/blog/?p=2678

Upper Receiver

Much like the lower, my basic understanding is that uppers are all pretty similar.  There are a few variations of design, but all function the same. Here are some of the variations:

A1 Style Upper: Has a fixed handle on the top.

A2 Style Upper: Has a fixed handle just like the A1, except that it has a rear sight with elevation and wind adjustments.

A3/A4 Style Upper: Sometimes called ‘flat top’. It has an accessory rail on the top for mounting any type of scope, sight, or A2 style removable handle. The A4 variation is effectively the same receiver, except that it has M4 style feed ramps that compliment the feed ramps on an M4 barrel. This actually rather confusing, so I’m dedicating a whole post to the M4 variation.

Forward Assist – This ‘button’ more / less serves a mechanical function of applying forward pressure on the bolt.  My understanding is that in certain combat situations, dirt, dust, and gunk can clog the upper and prevent the bolt from closing properly against the back of the round.  If this jamming occurs, you can slam the ‘forward assist’ to jam the bolt into position.  I’ve talked with AR range shooters who have never had to touch this button, and I don’t expect to have to use it either.  There are some variations of the Upper that don’t have the forward assist at all.

Dust Cover – Pretty straight forward.  It snaps closed… and when the bolt is moved forward or backward it pops back open.

Charging Handle – This works similarly to racking the slide on a semi-automatic pistol.  The charging handle allows you to bull the entire Bolt Carrier Group backwards and release it loading the first round into the chamber.  If you want to lock the bolt in the ‘back’ position, you similarly use the charging hand to pull the BCG back and engage the Bolt Catch.

T-Marks – A lot of listing for uppers mentioned having or not having ‘T-Marks’… WTF is that?  T-Marks are small white location indicators that are integrated into a Picatinny Rail system.  They’re used to note the location of an accessory should you decide to put it back after a re-location.  They simply count the number Picatinny Rail spaces… utilize them however you’d like.  Oh, and these are T marks because they’re on the TOP. A quad-rail hand-guard can have T-Marks, B-Marks, L-Marks and R-Marks.

Delta Ring Assembly

Includes Delta Ring, Barrel Nut, Weld Spring and Barrel Snap Ring.  This kit serves 2 functions: 1) Secures the Barrel to the Upper Receiver 2) Provides an attachment for the Hand Guard.  Some Hand Guards require a special type of assembly and are typically included with that Hand Guard if needed.

Hand Guard

Hand Guards or sometimes referred to as the ‘Forearm’ attaches to the Upper / Delta Ring assembly and serve as a ‘forward position’ place hold your rifle.  The Barrel gets pretty hot, so you don’t want to be stabilizing your rifle holding that!  Hand Guards come in all shapes and sizes, made of polymers and aluminum, etc etc.  The most common type I’ve seen is what they call a 4-Rail system.  Meaning is has 4 sets of Picatinny accessory rails on the top, bottom, left and right.  The correct length hand guard you purchase should correspond with the length of barrel you’re utilizing.  Typically, Carbine Length (16″ Barrel), or Rifle Length (20+” Barrel).  There are some Mid-Length hand-Guards that are designed to cover the Gas Block.  More on that below in the Gas Block section.

Free-Float Hand-Guards – There is a variation of the Hand-Guard referred to as Free-Float.  What this means is that the Hand-Guard only attaches to the upper at the rear position delta ring / barrel nut, and NOT again at the front gas block area.  The idea here is that by not letting the hand-guard touch the Barrel at all, any pressure exerted on the Hand-Guard doesn’t flex the barrel.  Even though this ‘flex’ of the barrel would be minimal, it is still a deviation in barrel angle and the effects are exacerbated by shooting distance.  These Hand-Guard designs are a touch more expensive as I’ve noticed, but increase rifle accuracy.  I’m sold.

Gas Block /  Gas Tube

The Gas Block attaches to the Barrel at the point where the ‘Gas Port’ is cut into the barrel.  Much like Hand-Guards, there are tons of different styles of these.  Some with Picatinny Rail systems, some without.  Above I mentioned that Mid-Length Hang-Guards were designed to cover the Gas Block… in that case, you need a ‘Low Profile’ Gas Block so there’s room for the Hand-Guard.  I think it’s safe to say that your Gas Block should be chosen to work as a pair with your choice of Hard-Guard.

The Gas Tube’s role is to transport the high pressure gas that was fielded by the Gas Block, and channel it back to the Upper Receiver and into the Gas Tube receiving end of the bolt.  The Barrel Nut is made so that once you get it tightened down, there’s only a small adjustment needed to feed the Gas Tube into the Upper Receiver.  WTF is all this needed for?  Check out the Gas System post for details on why this is necessary.

Flash Hider

This screws onto the threaded muzzle of the Barrel and comes in a multitude of designs.  The main purpose is to diffuse the muzzle flash from the rifle to make it less observable in battle.  It also typically has no cuts on the bottom so when firing in the prone position, no dust is kicked up into the air.

See all of this stuff in action! Check out this cool animation:

http://www.youtube.com/watch?v=FZipq6D6D9k