Is there a growing trend to shorter barrels on precision rifles?

In the past, most precision rifles have been manufactured with 24 to 26 inch barrels. Conventional wisdom in the past has been that it's necessary to sacrifice maneuverability to gain a more complete powder burn and significantly reduced flash signature. As is so often the case, the conventional wisdom of the day has proven to be wrong.

Projectiles in Motion

Internal ballistics is a very complex subject. Many things affect the internal performance of a given cartridge and bullet. These 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. As the bullet moves down the bore, the gas pressure behind it diminishes.
Given a long enough barrel, there will eventually be a point at 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 is not 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 playa major part. Rifles with high expansion ratios (smaller calibers) tend to lose less velocity than rifles with low expansion ratios (larger calibers).

Tactical Operations (Tac Ops) .308 Winchester (7.62x51mm NATO) caliber Tango 51 TM rifles typify the new thinking on the subject. Tac Ops considers 18 to 20 inches to be the optimal barrel length for the urban environment, with 18 inches preferred.

The Difference in Sizes

During the development of the Tango 51, Tac Ops took a standard 26 inch barrel and chopped it down to 18 inches in one inch increments. Between 1.0 and 20 rounds were fired from 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 which has become something of an industry standard. Going to an 18 inch barrel only results in a loss of 32 feet per second (fps).

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. The Los Angeles County Sheriff's Department's Special Enforcement Bureau (SEB) performed similar tests and came to similar conclusions.

Deputy Tom Lambrecht, who recently retired from the Department and who served for many years as SEB armorer and a Special Weapons Team long rifle expert, chronographed the Federal Match 168-grain BTHP rounds. Lambrecht said that, with the 20 inch Tango 51 that Tac Ops delivered to him, the muzzle velocity was averaging around 2,660 to 2,670 fps.

Many agencies prefer the 18 inch barrel for its added maneuverability. Even with a shorter barrel, you're still shooting around 2,630 fps with Federal Match. The target won't know if he's being hit with a bullet traveling 2,660 fps or 2,630 fps, and going to an 18 inch barrel doesn't effect the accuracy.

After initially going with the 20 inch barrel Tango 51s, the Los Angeles County Sheriff's Department has decided to go with the 18 inch barrel and Tac Ops 30 suppressor on all new Tango 51 s they purchase.

Physics of a Shorter Barrel

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. Using a shorter, heavier barrel minimizes accuracy robbing barrel vibration because a shorter barrel is stiffer and vibrates 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 smaller vibration nodes than longer barrels. Thicker barrels generally have smaller vibration nodes than slimmer barrels. The ringing frequency of a thicker barrel is higher and the oscillations are 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.

Shorter barrels do increase the muzzle blast and muzzle flash somewhat; however, from a practical standpoint, the differences between a 24 or 26 inch barrel and an 18 or 20 inch barrel are negligible.

Suppressor Use

Concerns over the muzzle blast and sound/flash signature can easily be eliminated by the use of a sound suppressor. The use of a suppressor provides a number of advantages to both the shooter and spotter. The use of a suppressor greatly reduces any ground disturbance and eliminates any muzzle flash/sound signature which 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 reduction in the muzzle blast and perceived recoil.

Tango Accuracy

Jerod Johnson, Leupold Law Enforcement and Military Representative/West Coast Division, who spent eight years as a Marine scout sniper, recently took his Tango 51, equipped with a Leupold Mark 4 M1 4.5-14 x 50mm Mil Dot illuminated reticule scope, to the known distance range portion of the 1st Marine Division Scout Sniper School. Marine Sgt. John Spurling was the marksmanship instructor at the school.

At the school, the Marines were shooting M40A1 and M40A3 rifles. Navy SEALS in attendance were shooting SR-25s. Johnson was shooting his Tango 51. They started off at 100 yards zero. Once they got their groups, Johnson went to 500 yards, shot four rounds rapid bolt, putting all rounds into the head of the target. Johnson then went to 600 yards, firing four rounds rapid bolt, again putting all rounds in the head. This was followed by ten rounds at 800 yards and ten rounds at 1,000 yards. At 800 yards, Johnson put all rounds once again in the head. At 1,000 yards, Johnson put nine rounds in the head and one in the neck. Johnson states, of all the rifles he has personally shot, the Tango 51 is, by far, the most accurate. As can be seen, the shorter barrel of the Tango 51 certainly doesn't hamper long-range accuracy.

How to Build a Better Rifle

Most of the ideas that Tac Ops has on building rifles came from the questions that they asked. They discovered that building an accurate rifle was really an engineering problem.

One thing that Tac Ops noticed was that many sporting rifles made out of old, loose military Mausers still shot extremely well. When Tac Ops investigated, they found out that the more accurate rifles all had snug, on axis chambers with minimum head space. This confirmed that cartridge alignment was critical and even more important than having a closefitting, expensive action. Later on, while reviewing the gun literature, Tac Ops found that the whole cartridge alignment and bullet fit issue was really resolved by the cast lead rifle bullet crowd. They proved that a long, correctly shaped throat and lead were critical to accuracy. While many reamers are excellent, Rescigno is adamant about only using JGS reamers because he considers the product to be the best - bar none - and their customer service, outstanding.

The answer to accuracy is basic - get the cartridge to correctly fit the barrel and correctly fit in the throat and keep from moving while it's fired. Beyond that, everything else besides the barrel is just support. For this reason, it's really important to remove as much of the receiver's influence on the cartridge as possible.

For information on the Tango 51, contact:
Tactical Operations, Inc.
433 North Camden Dr. 4th Fl. #239
Beverly Hills, Ca 90210
Phone 310 275-8797
Fax   323 933-3521
Email: blackops2@earthlink.net