AR-15 barrel profiles matter to a degree but also may not, depending on your intended application.
For most people, it won’t matter much. The average shooter is only going through a box or two at a time, a few times per year.
Nothing wrong with that and no judgement here at all – especially these days! – but that is generally the case.
There are also some proprietary profiles but almost everything boils down to a variation on a theme, with those themes being the common barrel profiles.
If you’re about to start an AR-15 build or swapping the barrel to a different one, this is an aspect to consider as it is something that will affect your rifle.
M4 And A2/Government
The M4 barrel profile and A2 aka Government profile are the most common. If you’re going to be conscious about barrel selection, they are also the most pointless.
The M4/A2 profile are the same, save for a cutout in the M4 barrel for mounting an M203 grenade launcher. The barrel narrows to 0.625 inches in diameter after the chamber, flaring to the gas block, and 0.75 inches in diameter up to the muzzle.
The A2 profile was developed for the M16A2. The story is that troops (in many versions of the story, Marines) were using the rifle’s barrel as a pry bar and would permanently bend the pencil barrel of M16A1s. The M4 profile includes a cutout for mounting a grenade launcher.
The benefit is a bit more weight up front, which ostensibly helps fight muzzle rise, but also leads to the main drawback of a front-heavy rifle. The extra material adds up to 8 ounces, sometimes more.
HBAR Barrel Profile
The HBAR barrel profile is a thick-to-slightly-less-thick tapered design, thinning after the gas block. It was developed to add heat resistance and make the barrel more durable.
They’re big and heavy at the back, which helps mitigate heat up to the gas block, which has some benefits. If you live to mag dump, the HBAR makes a certain amount of sense, but the intended application is precision target shooters.
The additional material between the chamber and the gas block is slower to heat, thereby slowing any potential shift of alignment due to minute heat deformation.
For the precision shooter, it’s an excellent choice, especially if you do a lot of shooting from prone or a bipod.
Pencil barrels were the original barrel profile for the AR-15/M16 as designed by Eugene Stoner, Jim Sullivan and Bob Fremont. The original barrel was 0.625 inches from front to back (with the gas block bulge in the middle) making the rifle light and handy.
Unfortunately, stress relieving and heat treating of the era weren’t what they are now.
As the barrel heated, it would ever so slightly warp (elastic deformation) and shift point of impact until it cooled. That’s why the M16 was switched to burst fire rather than full auto at one point.
This was not, of course, a benefit of the A2/M4 profile; the typical pencil contour is the same diameter as the A2/M4 barrel profile from the chamber to the gas block and that’s where heat stresses will manifest themselves.
Modern pencil/lightweight barrels, properly heat-treated and stress-relieved, aren’t as affected…but bear in mind that ANY barrel will shift point of impact if it gets hot enough.
The guys at InRange TV have a fantastic presentation on the topic. See it here:
Much of the conventional wisdom of pencil barrels is based on those older units. As you can see in the video, a modern pencil barrel shifts far less than an older Colt pencil barrel. However, a pencil barrel of modern manufacture that isn’t properly relieved and treated will too.
The SOCOM barrel is basically an M4/A2 in reverse. The barrel is thinner past the gas block and thicker from the chamber to the gas block, and with a cutout for mounting an M203 grenade launcher.
There are some more minor differences, including some stress relief cuts, but ultimately they barely add up to a significant difference for the civilian shooter. About the only benefit is a modest reduction in weight compared to an A2 or M4 contour, but a marginal one.
If you wanted a heavier barrel than a pencil, but not quite an A2/M4, this is the one to get.
There are a number of takes on the “bull barrel” style, but all add up to more or less the same thing: a big, heavy barrel.
Most are the A2/HBAR diameter of 0.750 inches, but some may be narrower or reduce diameter at various points.
The upsides and downsides are the same as A2/HBAR profiles, but the purpose is different. The idea is to stiffen the barrel as well as adding mass to reduce the effects of heat for the purpose of maximum accuracy, as bull barrels will typically have additional improvements for precision match shooting.
Bull barrels tend to be target barrels, so they will often – though not always! – be made of higher-grade materials than most HBAR or A2 barrels as they are going into a target rifle, with tighter clearances and tolerances for precision shooting.
Proprietary Profiles: Flutes And The Rest Of The Orchestra
Then you have proprietary AR barrel profiles, including fluted barrels, custom contours and so on.
Barrel contour designs are created for a few different reasons. It can be to add or reduce weight, it can be to increase durability and resistance to stress, or it can be to fit a specific shooting application.
It may also be some combination thereof, and it will be pretty obvious what the manufacturer has in mind.
How Much Do Barrel Profiles Matter?
How much do barrel profiles matter? Outside of a few specialized roles in the shooting sports and in the military, what the barrel contour affects is how the gun handles and where it balances.
If you’re just plinking a few times a year…you’re not going to care. If you’re training with your rifle or carbine or SBR a lot (as you should be) then it’s going to. Lighter profiles are easier for dynamic training, heavier barrels for heavy firing schedules with less movement.
The same applies for an AR pistol. A thinner pistol barrel is fine if you aren’t shooting it much. However, a heavy training and firing schedule may be a good reason to consider a thicker barrel profile to mitigate heat in the barrel.
There are some sporting applications where contour matters, such as for precision shooting. A shooter might want a lighter profile for easier handling in action shooting competitions (2 Gun, 3 Gun) or they may want a heavier barrel for muh split times.
The M4/A2 profile makes sense in a military context; you can’t be giving soldiers a delicate rifle. However, the armed civilian isn’t going to use their rifle as a pry bar or mount a grenade launcher.
If using an AR for hunting, a lighter barrel is going to be preferable if you do your hunting on foot. If stand hunting…it doesn’t matter as much!
So, those are the common AR barrel contours. Give it a think next time you put one together, or if you’re thinking about replacing yours.