[Bart B.]

jmr40' link http://www.tacticaloperations.com/SWATbarrel/ is both interesting and typical of what lots of published results of rifle tests say. But like so many of them, it doesn't tell the whole story and some of the data is questionable. Examples:

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 Tango 51 rifles will still shoot sub-1/4 MOA.

The accuracy of the Tango 51 isn't hampered by the shorter barrel. While at the range with the Tango 51 we were consistently getting sub-1/4 MOA accuracy at longer ranges? Well, the shorter barrel doesn't hamper longer range accuracy either.

As I mentioned in my article on the Tango 51, San Fernando (CA) PD Special Response Team long rifle marksman Chris Colelli once fired a 3-shot sub-1/4-inch group at the article appeared, Colelli fired a 3-shot group from the rifle at 700 yards that measured just under 2 inches center to center. The group, which was witnessed by several credible spotters, was shot off of a bipod with one small sandbag.

What's the size of the biggest groups fired? Are they too egotistical to publish that data? They obviously don't want folks to think about the larger ones even though that 2-inch 3-shot group was probably by far the smallest one shot and all the others were larger; much larger.

The very best benchrest rifles do not consistently getting sub-1/4 MOA accuracy at longer ranges; it's more like sub 3/4 MOA which is what their group agg's prove.

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.

What they don't mention is that any given barrel vibrates exactly the same for each shot fired for a given load. A different load makes it wiggle more or less, but the vibration frequency's the same.

If the bore's enlargement from normal to bigger as the barrel gets hot starting out cold, then nobody would be able to shoot a few dozen shots under 2 inches at 600 yards. That's been done but with bullets sorted to use only the perfectly balanced ones so the barrel could be tested for accuracy going from cold to very, very hot. They don't know what they're talking about. I think their problem was poorly fitted barrels or barrels not stress relieved properly.

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 invrement. 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).

Too many people have done similar tests, including SAAMI, and with bullets leaving in the 2500 to 3000 fps range muzzle velocity drops by 20 to 25 fps per inch the barrel's shortened. Maybe they used ammo with "barrel length sensors" in it so the powder would keep the same pressure requirements to push the bullet out at nearly the same velocity by changing the powder's burn properties. That claim's one worth "dishonorable mention" in my opinion.