Varying OAL on VLD's versus velocity

Discussion in 'Reloading' started by cowboy, Jul 7, 2009.

  1. cowboy

    cowboy Well-Known Member

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    Since Eric Stecker published his article on varying the OAL by .040 to find the sweet spot I figured I'd give it a try and see what would happen with a 280AI I have been using the 168 VLD's in. Right now I have them set at .015 off the lands. If I truly did find a better setting at say .130 off - anyone got any thoughts on what I might expect for a velocity difference. Right now I'm getting 2825 fps out of a 25" barrel using H4831sc. The reason I ask this is that I use a turret that is set at the 2825 and any drastic velocity change would mean some turret changes.
     
  2. royinidaho

    royinidaho Writers Guild

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    cowboy,

    you will get velocity and pressure changes with different seating depths. If I remember right the deeper the seat the higher the pressure. Another change usually happens when touching or jamming the rifling.

    My experience with a 270 Win would indicate on the extreme end of things at extended distances drop compensation would most probably be necessary on your turret.

    If I were you and she's shootin' good, I'd attempt to restrain he urge to dink around with it. Sounds to me like you have a very good thing going. Don't wear it out w/tinkeritus. Its a bad affliction.:D
     

  3. phorwath

    phorwath Well-Known Member

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    Roy & cowboy,
    Starting seated into the lands, velocity dropped for me as seating depth was increased with the Berger VLD.

    Same with the Henson HATs, except with those I started 0.030" off the lands. But velocity decreased as I increased seating depth.

    So I would say pressure and velocity drop as seating depth is increased. It leads me to wonder if changing the seating depth is really any different than leaving the seating depth constant and changing powder charges. Either way MV is being modified in the search for the sweet zone.
     
    Last edited: Jul 9, 2009
  4. royinidaho

    royinidaho Writers Guild

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    The way I see it is that as case volume increases, with long COL, pressure and thus velocity decreases. To maintain velocity a bit more powder is needed to maintain or increase the velocity.

    I usually push things enough, longest possible col, maximum amount of powder to where if I go from 215Ms to 215s I get into pressure signs.

    I'm one of those sorry folks that gets anxious over 20 fps.:rolleyes: I've been to counseling and thing I'm getting over it a bit.gun)
     
  5. phorwath

    phorwath Well-Known Member

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    I would add that the instructions provided with the HATs were to work up to a maximum load with the bullet 0.030" off the lands, and then increase seating depth while maintaining the same powder charge, while searching for the best accuracy. Increasing seating depth while maintaining constant powder charge is also the instruction from Berger. Neither company would provide these instructions if increasing the seating depth increased cartridge pressures (and consequently increase MV). It would be the more dangerous recommendation for load development and increase their liability if someone had a case rupture. If pressure and muzzle velocity increased with increased seating depths, then their recommendation would be start the farthest off the lands and decrease bullet seating depth, working the bullet closer into the lands.

    If we were to check with either Bounty Hunter or Lightvarmint, I'm certain both have described cartridge pressure and muzzle velocity decreasing as the bullet is seated deeper into the case, provided that powder charge is maintained at a constant charge weight.

    Someone else will sound in here pretty quick - no doubt. With the 338 265gr HATs, my muzzle velocity dropped about 30-35fps as seating depth was increased in 0.010" increments, starting at 0.030" off the lands and increasing seating depth to 0.070" off the lands.
     
  6. MontanaRifleman

    MontanaRifleman Well-Known Member

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    I believe I experienced this in load development with RL17 and the 180 E-tip out of a 300 WSM. At 68 gr with the bullet seated to fit the mag, ~.140 off the lands, I ran into pressure signs, with no pressure signs at 67.5 gr. That night I loaded some more @ 67.5 gr seated to .140 and .050 off the lands... and some @ 68 gr seated to .140 off the lands. There was a very slight stiff bolt vs a stiff bolt the night beore @ 68 gr, and the the two different seating depths @ 67.5 gr showed an average 8 fps slower for the longer COAL.

    -MR
     
  7. jmason

    jmason Well-Known Member

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    While we're on this topic did you note any substantial accuracy gains by changing the seating depth as described above while maintaining you charge weight? My thought would be it would just make the load go haywire again.

    If you did notice accuracy enhancement did you then go back and adjust your charge for the new found seating depth?

    "Inquiring minds want to know":)
     
  8. phorwath

    phorwath Well-Known Member

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    Yes, I did observe improved accuracy in the 0.050" off the lands seating depth in the initial range tests.

    Then when I was preparing to confirm that finding and fine tune powder charges, my scope blew a gasket. gun)gun) And I haven't been back out to the range with the 338 Edge since. Looking for a scope now, and having a tough time getting my hands on a Sightron SIII with mil-dot reticle.
     
  9. jmason

    jmason Well-Known Member

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    I haven't got that intense with loading yet. Once I get a good ES and some decent accuracy with just the powder charge I stop. My lengths are magazine or as far as I can set them.

    I did see some of those scopes on eBay but that's the only place.
     
  10. remingtonman_25_06

    remingtonman_25_06 Well-Known Member

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    I have noticed that if I keep powder charge the same but increase the OAL, I get a slightly lower muzzle velocity. I have noticed this with everything from a .222 rem to a 300 RUM.

    I always thought the longer the OAL, or the bullet was closer to the lands that it would create more pressure and that it would have a higher velocity. That just doesn't seem to be the case. I havne't done a whole lot of testing with my bullets in the lands because I cant get enough neck tension to keep them there, when I close the bolt it just seats them to the lands again.

    I just use a fired case, dent the neck, put a bullet in it, chamber the round and it will seat it relatively close to the lands, do that a couple times for an average and thats where I start my seating depth. At most, I'm .010" off which is where all my guns shoot well, either at the lands or no more then .010" off.