There’s a growing trend to shorter barrels on tactical precision rifles. In years past, a 24- to 26-inch barrel was practically a given. Accepted wisdom was that it was necessary to sacrifice a little maneuverability to gain a more complete powder burn and significantly reduced flash signature. Today, precision rifles with significantly shorter barrels are commonplace.
The desire for more maneuverable rifles for the urban setting led manufacturers to come out with shorter-barreled precision rifles. This brings up some obvious questions. How short is too short? What sacrifices, if any, are made by going to a shorter barrel?
To answer these questions, we must first start by taking a look at the subject of internal ballistics. Internal ballistics is a very complex subject. There are many factors which affect the internal performance of a given cartridge and bullet. Factors affecting internal performance include the powder chamber capacity; load density; amount and burning characteristics of the propellant powder; temperature of the propellant prior to ignition; uniformity and speed of ignition; diameter, weight and bearing length of the bullet; and the length of the barrel and its interior dimensions.
Longer barrels give the powder more time to work on propelling the bullet. For this reason longer barrels generally provide higher velocities, everything else being equal. However, the gas pressure behind the bullet diminishes as the bullet moves down the bore. Given a long enough barrel, there will eventually be a point in which the bore friction and air pressure in front of the bullet will equal the gas pressure behind it. At this point, the velocity of the bullet will start to decrease.
There isn’t any clear-cut answer as to how much velocity will be lost per inch of barrel length reduction. The amount of loss is closely tied to the expansion ratio. As previously noted, the type and amount of powder, as well as the weight and bearing length of the bullet, also play a major part. Rifles with high expansion ratios (smaller calibers) tend to lose less velocity than rifles with low expansion ratios (larger calibers).
Custom precision rifle maker Tactical Operations, Inc. (Tac Ops) was led in the trend to shorter-barreled precision rifles with the introduction of tits groundbreaking 308 Winchester (7.62x51mm NATO) caliber Tango 51™ rifle. Tac Ops considers a barrel of length of 18 to 20 inches to be optimal for the urban environment, with 18 inches the preferred length.
During the development of the Tango 51, Tac Ops took a standard 26-inch barrel and cut it down to 18 inches in one-inch increments. Between 10 to 20 rounds were fired at each increment. They found that a 20-inch barrel provides for a complete propellant burn and no velocity loss when using Federal Match 168-grain BTHP, a cartridge that has become something of a law enforcement standard. Going to an 18-inch barrel only resulted in a loss of 32 feet per second (fps).
Shorter barreled rifles are more versatile, being equally suitable for both urban and rural operations. According to Tac Ops, there isn’t any need to go to the 26-inch barrel unless you want to go to a heavier bullet or push the round to higher velocity using more powder or use a slower burning powder.
The Los Angeles County Sheriff’s Department’s Special Enforcement Bureau (SEB) performed tests similar to those conducted by Tac Ops and came to similar conclusions. The late Tommy Lambrecht, who at the time was SEB armorer and Special Weapons Team long rifle expert, chronographed the Federal Match 168-gr. BTHP rounds. Lambrecht said that the muzzle velocity was averaging around 2,660 to 2,670 feet per second (fps) from the 20-inch-barreled Tango 51 that Tac Ops delivered to him.
Although the 20-inch barrel remains very popular, many agencies prefer an 18-inch barrel for its added maneuverability. With the 18-inch barrel, you’re still shooting around 2,630 fps with Federal Match. The target certainly isn’t going to know if he’s being hit with a bullet that leaves the muzzle at 2,660 fps or 2,630 fps. The terminal ballistics are identical.
Going to an 18-inch barrel doesn’t adversely effect the accuracy of the rifle. Tac Ops has achieved incredible accuracy with the shorter barrels. The 18-inch barreled Tac Ops rifles are still capable of shooting sub-1/4 MOA. The performance is just as good with the 18-inch barrel as it is with the 20-inch barrel out to a distance of 600 yards.
Shorter barrels are actually often more accurate than their longer counterparts. A rifle barrel is a cantilevered beam and as such they sag. More sag results in more whip and vibration as the bullet travels down the bore. Barrel sag induces longitudinal stress that can cause stringing of shots. Using a shorter, heavier barrel minimizes reduces stress and accuracy-robbing barrel vibration. A shorter barrel is stiffer and vibrates at a less.
Barrel length and contour determines the relative “stiffness” of a barrel, i.e., how much a barrel will tend to vibrate. Shorter barrels generally have oscillations of smaller amplitude. than longer barrels. Thicker barrels generally have fewer vibration nodes than slimmer barrels. The ringing frequency of a thicker barrel is higher and the oscillations are of a smaller amplitude and of a shorter duration. This equates to less barrel motion at the muzzle. The use of a shorter barrel also allows the use of a heavier contour without making the rifle unwieldy.
The use of a heavier contour tends to provide less variation between a cold shot and any subsequent follow-up shots. Barrels expand as they heat up. As the barrel expands any stress on or in the barrel will cause stringing of the shots. Bore expansion results in an increase in group size. Heavier barrels tend to be more consistent because they take longer to heat up.
An 18- to 20-inch barrel may be fine for a caliber like the .308 Win., but what about calibers such as the .300 Winchester Magnum (7.62x66B)? Many agencies are opting for this cartridge as a result of its long range ballistics.
The .308 Win. has a maximum effective range of about 800 yards. While this is certainly more than enough for most law enforcement scenarios (law enforcement snipers rarely have to engage targets at more than 100 yards), the .300 Win. Mag. does increase the maximum effective range by an additional 300 yards, for a maximum effective range of about 1,100 yards. The .300 Win. Mag. is also a flatter shooting cartridge at all ranges, although this comes with the price of additional recoil and overpenetration concerns that need to be addressed.
Many law enforcement agencies purchasing a .300 Win. Mag. will primarily be employing the rifle in an urban environment. The common reason for opting for the .300 Win. Mag. that it extends the capabilities of the rifle to longer ranges than the .308 Winchester is capable in those rare situations where longer range capability is necessary. One example is airports where longer range shots may be necessary in a counterterrorism/counterhijacking role. This leads to an obvious question. Will going to a shorter barrel for added maneuverability in the urban environment adversely affect long range performance of a rifle in this caliber?
Back in the 90s, to find the answers, Tac Ops took a 26-inch barreled .300 Win. Mag. and chopped the barrel down in one-inch increments as they previously did with the .308 Winchester. Ten rounds of Federal Match 190-grain BTHP Gold Medal were fired from each increment. No velocity was lost from 26 inches to 22 inches. Velocity loss started to occur only after they went below 22 inches.
But that was then. This is now. According to Michael Rescigno, President of Tac Ops, you can now even go to a 20-inch barrel on Tac Ops .300 Win Mag rifles and still get outstanding performance using the 190-grain Federal Match ammo. This is the direct result of Tac Ops newest proprietary chamber reamer. The new reamer provides a tighter chamber with higher pressures. The Tac Ops rifles still provide 1/4-MOA or better accuracy.
At this point, I can hear readers asking, “What about muzzle blast and muzzle flash? Won’t they be a problem with the shorter barrels?” These are valid concerns. With both calibers, shorter barrels do increase the muzzle blast and muzzle flash somewhat. It’s not as much as one might expect. From a practical standpoint, the differences between a 24- or 26-inch barrel and an 18- or 20-inch barrel are negligible, except when slow burning powders are used.
Any concerns over the muzzle blast and sound/flash signature can easily be eliminated by the use of a sound suppressor (silencer). With today’s compact, low-maintenance suppressors, such as the Tac Ops 30, there’s no reason that all tactical precision rifles shouldn’t be so equipped. More and more law enforcement agencies are coming to this conclusion.
The use of a sound suppressor provides a number of advantages to both the shooter and spotter. The suppressor greatly reduces any ground disturbance and eliminates any muzzle flash/sound signature that can identify the position or disturb vision and hearing. There isn’t any necessity for the shooter or spotter to wear hearing protection. Many shooters find that their accuracy improves when a suppressor is employed due to the resulting reduction in the muzzle blast and recoil. The reduction in recoil also permits quicker follow-up shots.
A sound suppressor can substantially reduce the recoil velocity and recoil energy of a rifle. Gas volume and gas pressure at the muzzle are major factors in the free recoil energy produced by a rifle. Shorter barrels generally result in increased gas volumes and higher gas pressures at the muzzle. All other factors being equal, increased gas volumes and higher gas pressures at the muzzle will increase the recoil velocity and free recoil energy.
Free recoil energy is proportional to the square of the recoil velocity of the rifle. Doubling the recoil velocity quadruples the free recoil energy. Sound suppressors reduce the free recoil energy by suppressing the effects of the expanding powder gasses. They also add weight, slowing the acceleration of the rifle.
In summary, the appropriate barrel length is closely tied to the caliber and the load or loads that will be employed. If a shorter barrel provides equivalent or better accuracy and little or no loss in velocity, why go to a longer barrel? Why sacrifice maneuverability and add excess weight? While old attitudes may die hard, chronographs and ballistics don’t lie. Shorter barrels are often better. The proof is in the performance.
Tactical Operations, Inc.
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