Barrels Tight or Loose ??

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by bjlooper, May 16, 2006.

  1. bjlooper

    bjlooper Well-Known Member

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    I read several times on this fourm comments that a certian barrel manufactures barrles are loose (Pacnor) or that anothers barrels are tight (Lilja).
    What diffrence does tight or loose make in regards to: Accuracy, velocity, and longevity.
    Thanks
    DR B
     
  2. Fiftydriver

    Fiftydriver <strong>Official LRH Sponsor</strong>

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    BJlooper,

    Well, in general terms, a loose barrel will allow higher velocities because the bullet is not swaged down in diameter as much as it is with a tighter bored barrel.

    Those wanting to shoot hard bullets will especially see this although a loose barrel used with a bullet such as a Barnes X bullet will aften see poor accuracy results because the hard, solid bullet will not bump up under pressure to fill the bore diameter if slightly larger then the bullet diameter.

    A tight bore is generally more accurate because the bullet does not have to bump up under pressure much if any for a quality fit to the bore.

    Velocity may be limited because it takes more force to drive a bullet through a smaller diameter hole then a larger one but accuracy generally is better.

    As far as barrel life, I am not sure there would be much difference at all as long as the loose bore is not so large as to allow gas to pass around the bullet body and cause flame cutting.

    In all honesty, the difference between loose and tight can be measured usually by less then 1/2 thou. Most aftermarket barrels are pretty tight on average. I would say Lilja barrels are some of the tightest and this may result in lower velocity potential.

    May seem kind of strange that these barrels are the ones I use exclusively in my Allen Magnums as they are based on high performance but I will take extreme accuracy over an extra 50 fps any day of the week.

    Again, I would say the difference between say a Lilja, Rock, Broughton, Hart or Kreiger in bore diameter would be very small if any. There is a reason all of these are very good shooting barrels.

    It is not as big a deal as some believe it is but there are some differences, mainly velocity potential, although this is pretty small.

    If someone is saying they are getting +100 fps more velocity with one barrel brand over another, all else being equal, I would find that hard to believe without a change in pressure.

    Good Shooting!!

    Kirby Allen(50)
     

  3. Bart B

    Bart B Well-Known Member

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    [ QUOTE ]
    What diffrence does tight or loose make in regards to: Accuracy, velocity, and longevity.

    [/ QUOTE ]Accuracy wise, the groove diameter should be at least .0003- to .0005-inch smaller than bullet diameter. I've shot .3092-inch bullets in a .3077-inch groove diameter barrel with excellent accuracy. Military rifle team members using the M14NM rifles with arsenal barrels liked the M118 7.62mm NATO match ammo with bullets about .3086-in. diameter. These barrels wouldn't shoot Sierra's .3082-inch bullets (nor others of the same diameter or a bit smaller) as their groove diameters were typically about .3083-inch. Many of these guys had two M14's; one called a "Lake City" one for M118 ammo and the other a "Sierra" one for 168 and 180 grain HPMK's.

    Velocity wise, tighter barrels typically shoot bullets faster than loose ones. The best example of this was the same rifles used by the military teams. When Lake City Arsenal came out with their M852 match ammo with Sierra 168's in them, the loose 22-inch barrels on M14 (and civilian M1A) rifles usually wouldn't shoot them fast enough to stay supersonic through 1000 yards. Tight barrels with .3075-inch groove diameters did as they chronographed the same load about 100 fps faster than a loose barrel. But not enough people used barrels that tight so Lake City Arsenal started using Sierra 175's in their match ammo and that solved the problem as they left at the same speed but have a higher ballistic coefficient.

    I've also had higher velocity out of tighter barrels of the same length and chamber dimensions with the same load. In Great Britain where aresnal ammo has to be used in most long range matches, they have to use .3065-inch groove diameter barrels to shoot their 147-gr. .3075-inch diameter NATO bullet out fast enough to stay supersonic through 1000 yards.

    Barrel life is about equal between them.
     
  4. Fiftydriver

    Fiftydriver <strong>Official LRH Sponsor</strong>

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    [ QUOTE ]
    Velocity wise, tighter barrels typically shoot bullets faster than loose ones. The best example of this was the same rifles used by the military teams. When Lake City Arsenal came out with their M852 match ammo with Sierra 168's in them, the loose 22-inch barrels on M14 (and civilian M1A) rifles usually wouldn't shoot them fast enough to stay supersonic through 1000 yards. Tight barrels with .3075-inch groove diameters did as they chronographed the same load about 100 fps faster than a loose barrel. But not enough people used barrels that tight so Lake City Arsenal started using Sierra 175's in their match ammo and that solved the problem as they left at the same speed but have a higher ballistic coefficient.


    [/ QUOTE ]

    I would have to agree and disagree with you on this one. Yes, if you take the same ammo and shoot it in two different rifles, the one that has the tighter bore will produce higher velocity, for one simple reason, the pressure increases.

    I do not believe the original question was pertaining to using a standard mil spec ammunition though.

    If you take two barrels with different bore diameters and load them both to the same pressure level, say 60,000 psi. The larger diameter bore will produce higher velocities on average then the smaller diameter bore.

    Simple reason, it takes more pressure to drive a bullet down a tighter hole then it does a larger hole.

    In your comparision you are correct but I do not feel that is relative to the question at hand here.
     
  5. Bart B

    Bart B Well-Known Member

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    [ QUOTE ]
    I do not believe the original question was pertaining to using a standard mil spec ammunition though.

    If you take two barrels with different bore diameters and load them both to the same pressure level, say 60,000 psi. The larger diameter bore will produce higher velocities on average then the smaller diameter bore.

    [/ QUOTE ]Yes, Kirby, I know all that.

    I used a given ammo type as a base to compare two different groove (not bore) diameter barrels and changing only one element of the hypothetical experiment. Changing two elements is bad data collection methodology to see a difference. My own handloads did the same thing with loose and tight barrels. I thought one could tell that.

    And yes, the larger groove (again, not bore) barrel will shoot the same bullet faster with the same pressure; there's more force pushing it 'cause there's more area for the pressure to push on. This assumes the bullet will upset to groove diameter preventing gas blow by leaks, too. But you gotta put more powder in to reach the same pressure curve levels 'cause there's more volume inside the barrel.