So what does a "service rifle" AR-15 look like?

This is an AR-15 pattern rifle approximating an "M4 Carbine".
The accessories are based on the circa-1997 SOPMOD Block 1 accessory kit.

While this is the image many of us see when thinking of an "M4 Carbine", there are countless possible configurations.

Below is a typical "A2 National Match" configured AR-15 pattern rifle.

While iron sights have fallen out of favor among competitors, the 20" barrel, clamshell, and fixed A2 stock are all but ubiquitous at the top.

Why? Well, one of the most important properties of a competition service rifle is recoil.
The more recoil a rifle has, the harder it is to maintain your sight picture and position while shooting.

Clamshell handguards and fixed A2 stocks both make it easy for shooters to add extra weight to a rifle.
Similarly, a 20" barrel weighs more than a 16" barrel (the minimum / standard barrel length for AR-15 pattern rifles).
You also get a little more velocity, which gives your shots a flatter trajectory out to farther ranges. The combination of all this increased weight can dramatically lower the recoil impulse of a rifle.

Another benefit of the 20" barrel (which also applies to 18" barrels) is a smoother and slower recoil impulse.

18" and 20" barrels have "rifle-length" gas system.
"Rifle length" gas systems are longer than "mid-length" or "carbine" systems common on 16" barrels.
The length of the gas system has to do with how far forward of the chamber the gas port is milled.

The further forward the gas port is (e.g. a longer gas system), the longer it takes for gas to enter the gas tube.
The longer it takes for gas to enter the gas tube, the longer it takes for the bolt to start unlocking.
This is known as "dwell time", and a longer dwell time spreads out the recoil impulse and feels "smoother".

In 2016, the CMP / NRA updated their rulebooks to allow optics of up to 4.5x magnification on allowed service rifles.
This reflects the fact that optics are now commonplace on standard infantry rifles (ACOG / M68 CCO have been in use for a while).

As a result, a typical service rifle you might see at Camp Perry would look something like this:

It carries over a 20" barrel and clamshell handguards from the A2 National Match rifle, while adding a scope and a modern "precision" stock.


Last, and generally in this form of competition, least, you have a typical modern "tactical" AR-15:

While these will get the most likes on Instagram or upvotes on Reddit, they are not optimal for service rifle matches.
Previously, weight was mentioned as an important property of a rifle - but it is closely linked with a rifle's balance.

The balance of a rifle generally refers to where its center of gravity is. Generally, most rifles tend to be "front heavy".
The heaviest part of most rifles is often the barrel, which is forward of the grip, causing the center of gravity to be far towards the front.

If you look at the two rifles labeled National Match, you'll notice both of them have large, bulky looking stocks.
Both of these stocks allow the shooter to insert lead weights into the stock to move the center of gravity backwards.
This makes it easier to shoot the rifle, especially in the offhand stance.

To summarize the desirable attributes in a service-rifle AR-15:

• High-quality barrel from a reputable manufacturer (Krieger, Bartlein, Shilen, Criterion)
  • 18" or 20" barrel (rifle-length gas)
  • 5.56 or .223 Wylde chambering
• Crisp, match-focused trigger (Geissele, Rock River, LaRue)
  • Two stage
  • 4.5 lbs minimum pull weight
• Heavy, solid stock (Magpul, Colt)
  • Optional: capable of accepting lead weights