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BARREL LENGTH & THE PERCISION RIFLE

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 Posted 4/15/2012 7:37:30 AM
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BARREL LENGTH AND THEPRECISION RIFLE
Why shorter barrels may often be better
by 
Eugene Nielsen

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.  Acceptedwisdom was that it was necessary to sacrifice a little maneuverabilityto gain a more complete powder burn and significantly reduced flash signature. Today, it’s not uncommon to rifles with significlly shorter barrrels.

 Attitudes are are changing. The desire for more manueverable rifles for the urban setting has led agrowing number of manufacturer's to come out with shorter-barreled precisionrifles.  This brings up an obvious question  -- how short istoo short?  What sacrifices, if any, are made by going to a shorterbarrel?

 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 factorswhich 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 ofignition; diameter, weight and bearing length of the bullet; and the lengthof the barrel and its interior dimensions.

 Longer barrels givethe powder more time to work on propelling the bullet.  For this reasonlonger barrels generally provide higher velocities, everything else beingequal.  However, the gas pressure behind the bullet diminishes asthe bullet moves down the bore.  Given a long enough barrel, therewill eventually be a point in which the bore friction and air pressurein front of the bullet will equal the gas pressure behind it.  Atthis point, the velocity of the bullet will start to decrease.
 
 

Shorterbarrels are capable of surprising long-range accurancy. San Fernando (California)PD Special Response Team long rifle marksman Chris Colelli, shown here,fired a three-shot group at 700 yards that measured just under two inchescenter-to-center. Colleli also fired a sub-1/4- inch group at 200 yards.The target is now framed and hanging in his lieutenant's office.
 There isn't any clear-cutanswer 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 previouslynoted, the type and amount of powder, as well as the weight and bearinglength of the bullet, also play a major part.  Rifles with high expansionratios (smaller calibers) tend to lose less velocity than rifles with lowexpansion ratios (larger calibers). 

 Tactical Operationsabout in the April 2000 issue of  S.W.A.T., typifies the trend torifles with shorter barrels.  Tac Ops considers a barrel of lengthof 18 to 20 inches to be optimal for the urban environment, with 18 inchesthe preferred length.

 During the developmentof the Tango 51, Tac Ops took a standard 26-inch barrel and cut it downto 18 inches in one-inch increments.  Between 10 to 20 rounds werefired at each invrement.  They found that a 20-inch barrel providesfor a complete propellant burn and no velocity loss when using FederalMatch 168-grain BTHP, a cartridge that has become something of a law enforcementstandard.  Going to an 18-inch barrel only resulted in a loss of 32feet per second (fps).

 Shorter barreled riflesare 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 barrelunless you want to go to a heavier bullet or push the round to higher velocityusing more powder or use a slower burning powder.  The Los AngelesCounty Sheriff's Department's Special Enforcement Bureau (SEB) performedtests similar to those conducted by Tac Ops and came to similar conclusions. 
 

 Tommy Lambrecht, SEBarmorer and Special Weapons Team long rifle expert, recently chronographedthe Federal Match 168-gr. BTHP rounds.  Lambrecht said that the muzzlevelocity was averaging around 2,660 to 2,670 feet per second (fps) fromthe 20-inch-barreled Tango 51 that Tac Ops delivered to him. The accuracy of theTango 51 isn't hampered by the shorter barrel.  While at the rangewith the Tango 51 we were consistently getting sub-1/4 MOA accuracy atlonger ranges?  Well, the shorter barrel doesn't hamper longer rangeaccuracy either.

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

LosAngeles County Sheriff's Department Special Enforcement Bureau (SEB) SpecialWeapons Team long rifle experts Fred Keelin (left) with Tac Ops Alpha 66
 Colelli is a superbmarksman, one of the best that I've seen, but he would be the first toadmit that an element of luck played a role in this feat.  Groupslike these certainly aren't typical of what could be realistically expectedunder actual operational conditions.  Still, they show that the rifleis capable of phenomenal accuracy provided that the operator does his orher part.

 Although the 20-inchbarrel remains very popular with agencies purchasing the Tango 51, many agencies prefer an 18-inch barrel for its added maneuverability. With the 18-inch  barrel, you're still shooting around 2,630 fps withFederal Match.  The target certainly isn't going to know if he's beinghit with a bullet that leaves the muzzle at 2,660 fps or 2,630 fps. The terminal ballistics are identical.

 Going to an 18-inchbarrel doesn't adversely effect the accuracy of the rifle.  Tac Opshas achieved incredible accuracy with the shorter barrels.  The 18-inchbarreled Tango 51 rifles will still shoot sub-1/4 MOA.  The performanceis just as good with the 18-inch barrel as it is with the 20-inch barrelout to a distance of 600 yards.  After initially going with the 20-inchbarrel for their Tango 51s, the Los Angeles County Sheriff's Departmenthas decided to go with the 18-inch barrel and Tac Ops 30 suppressor onall new Tango 51s that they purchase. 

 Shorter barrels areactually often more accurate than their longer counterparts.  A riflebarrel is a cantilevered beam and as such they sag.  More sag resultsin more whip and vibration as the bullet travels down the bore.  Barrelsag induces longitudinal stress that can cause stringing of shots. Using a shorter, heavier barrel minimizes reduces stress and accuracy-robbingbarrel vibration.  A shorter barrel is stiffer and vibrates at a less.

 Barrel length and contourdetermines the relative "stiffness" of a barrel,  i.e., how much abarrel will tend to vibrate.  Shorter barrels generally have oscillationsof smaller amplitude. than longer barrels.  Thicker barrels generallyhave fewer vibration nodes than slimmer barrels.  The ringing frequencyof a thicker barrel is higher and the oscillations are of a smaller amplitudeand of a shorter duration.  This equates to less barrel motion atthe muzzle.  The use of a shorter barrel also allows the use of aheavier contour without making the rifle unwieldy.

 The use of a heaviercontour tends to provide less variation between a cold shot and any subsequentfollow-up shots.  Barrels expand as they heat up.  As the barrelexpands any stress on or in the barrel will cause stringing of the shots. Bore expansion results in an increase in group size.  Heavier barrelstend to be more consistent because they take longer to heat up. 

 An 18- to 20-inch barrelmay be fine for a caliber like the .308 Win., but what about calibers suchas the .300 Winchester Magnum (7.62x66B)?   Many agencies areopting for this cartridge as a result of its long range ballistics. The .308 Win. has a maximum effective range of about 800 yards.  Whilethis is certainly more than enough for most law enforcement scenarios (lawenforcement snipers rarely have to engage targets at more than 100 yards),the .300 Win. Mag. does increase the maximum effective range by an additionalthis comes with the price of additional recoil. 

 Many agencies purchasinga .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 thecapabilities of the rifle to longer ranges than the .308 Winchester iscapable in those rare situations where longer range capability is necessary. This leads to an obvious question -- will going to a shorter barrel foradded maneuverability in the urban environment adversely affect long rangeperformance of a rifle in this caliber?

 To find the answers,Tac Ops took a 26-inch barreled .300 Win. Mag. and chopped the barrel downin one-inch increments as they previously did with the .308 Winchester. Ten rounds of  Federal Match 190-grain BTHP Gold Medal were firedfrom each increment.  No velocity was lost from 26 inches to 22 inches. Velocity loss started to occur only after they went below 22 inches.

 As a result of theirtests, Tac Ops decided not to go below 22 inches on their .300 Win. Mag.tactical precision rifle, the Alpha 66.  According to Mike Rescigno,President of Tac Ops, the 22-inch barrel is ideal for the tactical shootersthat are going to use the 190-grain Federal Match ammo.  There isn'tany loss of performance by going to the 22-inch barrel and this round. The Alpha 66 still provides 1/4-MOA or better accuracy.

 For heavier bulletsor hotter loads with slower burning powders, Rescigno recommends a 24-to 26-inch barrel.  The longer barrel length is necessary for completepowder combustion with these loads.  Rescigno adds that he has a 24-inchbarrel on his personal .300 Win. Mag. just in case he wants "to shoot theheavier 220-grain bullets with a lot of powder." 
 
 

TOP:After testing and evaluation, the SEB has decided to go with an 18-inchbarrel on all new .308 Win. Tango 51s, and a 22-inch barrel on all .300Win Mag. Tactical precision rifles. Fred Keeling (left) is shown with witha suppressed 18-inch-barreled Tango 51 .308 Win., and Guy Geisler (right) is shown with a 22-inch-barreled Alpha 66 .300 Win. Mag.BOTTOM:The optional barrel length is closely tied to the loads that will be employed.There is no loss of performance from the .300 Win. Mag. Federal Match 190-grainBTHP when fired from barrels as short as 22 inches. The above Alpha 66has Tac Ops muzzle brake  installed. 

 At this point, I canhear readers asking, "What about muzzle blast and muzzle flash?  Won'tthey be a problem with the shorter barrels?"  These are valid concerns. With both calibers, shorter barrels do increase the muzzle blast and muzzleflash somewhat.  It's not as much as one might expect.  Froma practical standpoint, the differences between a 24- or 26-inch barreland an 18- or 20-inch barrel are negligible, except when slow burning powdersare used.

 Any concerns over themuzzle blast and sound/flash signature can easily be eliminated by theuse of a sound suppressor (silencer).  With today's compact, low-maintenancesuppressors,such as the Tac Ops 30, there's no reason that all tactical precision riflesshouldn't be so equipped.  More and more law enforcement agenciesare coming to this conclusion. 

 The use of a soundsuppressor provides a number of advantages to both the shooter and spotter. The suppressor greatly reduces any ground disturbance and eliminates anymuzzle flash/sound signature that can identify the position or disturbvision and hearing.  There isn't any necessity for the shooter orspotter to wear hearing protection.  Many shooters find that theiraccuracy improves when a suppressor is employed due to the resulting reductionin the muzzle blast and recoil.  The reduction in recoil also permitsquicker follow-up shots. 

 A sound suppressorcan substantially reduce the recoil velocity and recoil energy of a rifle. Gas volume and gas pressure at the muzzle are major factors in the freerecoil energy produced by a rifle.  Shorter barrels generally resultin increased gas volumes and higher gas pressures at the muzzle. All other factors being equal, increased gas volumes and higher gas pressuresat the muzzle will increase the recoil velocity and free recoil energy.

 Free recoil energyis proportional to the square of the recoil velocity of the rifle. Doubling the recoil velocity quadruples the free recoil energy.  Soundsuppressors reduce the free recoil energy by suppressing the effects ofthe expanding powder gasses.  They also add weight, slowing the accelerationof the rifle.

 In summary, the appropriatebarrel length is closely tied to the caliber and the load or loads thatwill be employed.  If a shorter barrel provides equivalent or betteraccuracy and little or no loss in velocity, why go to a longer barrel? Why sacrifice maneuverability and add excess weight?  While old attitudesmay die hard, chronographs and ballistics don't lie.  Shorter barrelsare often better.  The proof  is in the performance.
 

 

http://www.tacticaloperations.com/SWATbarrel/SOURCE

Tactical Operations, Inc. 
433 North Camden Dr. 4thFl. #239
Beverly Hills, Ca 90210
Phone 310 275-8797
Fax   323 933-3521


 


The Spike! for Freedom

Edited: 4/15/2012 7:53:19 AM by SpikeDefender
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 Posted 8/12/2012 8:08:15 PM
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personally prefer the Army Drill team because they do way more elaborate throws.

Next would be the Marine Silent Drill team because I love the percision but find their routines get very repetitive and just a lot of rifle spinning.

I haven't seen enough of the Navy or Air Forces teams to really hold an opinion.

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