Excessive headspace=lower muzzle velocity?

Discussion in 'Reloading' started by PapaChunk, Dec 31, 2011.

  1. PapaChunk

    PapaChunk New Member

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    Hi everyone first time poster so go easy one me.:D My question for you all is, does excessive headspace cause a slower muzzle velocity? Yesterday I went out to do some shooing at 700 yards. Using the same amount of elevation I always use I shot about three rounds at some steel. I noticed that the rounds were hitting about 7-10 inches low. I didn't give it much thought just dialed up some more elevation and started shooting again. Used this new dope for the rest of the time and was on target. Later that night I was cleaning up my brass and noticed that almost all of them had signs of thin wall around the case head. Brass had only been reloaded twice before. Checked some of the rounds that I had not shot yet with a hornady headspace gauge and notice the shoulders had been pushed back to far and causing to much headspace. Unfired brass was a little over 0.010" shorter than the fire cases. I reset my sizing die to fixed this issue. Anyway I got to thinking and was wonder if the excessive headspace caused my rounds to go low. I was thinking that since the brass and to expand more to fill the chamber that it would cause a loss in pressure resulting in a slower muzzle velocity. Am I thinking straight or just making excuses? Thanks.
     
  2. Loner

    Loner Well-Known Member

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    I think you have it right. Energy spent stretching that case was not spent on pushing
    the bullet.
     

  3. bassin93

    bassin93 Well-Known Member

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    temp will also play havoc on your velocity even using extreme powders. did you use a setting from a summer (warmer) velocity reading and now shooting in a colder enviroment? I lost 50fps in my edge from 75-80 degrees to now 35-45 degrees.
     
  4. joe0121

    joe0121 Well-Known Member

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    Excessive headspace = Blowed up gun. :(
     
  5. woods

    woods Well-Known Member

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    What caliber and was the brass new brass, once fired or fired multiple times

    What signs, do you have pics and how did you determine the signs

    .010" is not un-normal for an unbelted case going from a new case to a fired case. My Steyr 30-06 is .011". When you say the "shoulders had been pushed back too far", what was the difference in the measurements between the cases with the shoulders pushed back too far and a new case? A little more info

    Normally it takes so little pressure to expand the brass case in comparison to the pressures inside the chamber that it has little to no effect on pressure and velocity.
     
  6. PapaChunk

    PapaChunk New Member

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    .308 Win
    twice fired winchester brass


    Shiny ring around case head.




    Brass fired from my rifle measure 1.625" before resizing. My sizing die was pushing the shoulder back roughly .010" to 1.616". Normally I like to bump the shoulder back only .003"-.002" to avoid over stretching the brass. New winchester brass was measuring 1.616"



    This was what I was really wanting to know. So you are saying that difference in headspace will not affect my point of impact.

    Thanks for the replies.
     
  7. MNbogboy

    MNbogboy Well-Known Member

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    In my experience any change will very likely change POI especially at longer ranges....Imagine changing your seating depth .010...let alone case capacity...
    IMHO,
    Randy
     
  8. Mikecr

    Mikecr Well-Known Member

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    No. Same powder amount in a smaller case reduces barrel time, and possibly increases velocity. It won't decrease velocity.
     
  9. MNbogboy

    MNbogboy Well-Known Member

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    Mikecr has a good point, that a decrease in case capacity will probably not decrease MV to the degree you are talking about....You didn't mention if you were able to confirm the 7 to 10" change in POI with chronograph results...It is entirely possible to have that much difference in POI without much of a change in velocity in either direction...Barrel harmonics will always affect POI....And a change in case dynamics will most likely affect the measurable barrel harmonics...Again due to all the variables that most often come into play such as ambient temperature as Bassin93 mentioned....It is hard to say what exactly happened without all the stats...
    An example is; both of my 260s always are slower with new brass (smaller in capacity and contradictory to Mikecr's theory) but burn rates complicated with the reflectivity of the inner case walls of the "shiny" new brass may attribute to this(my theory).....Second neck sized firings are a little faster and three and on fired cases stabilize just a tad under the second fired cases (now confirming Mikecr's theory)....
    We can speculate all we want but this really is rocket science...We can only do our best to produce the most repeatable ammunition and deliver it in a redundant action to our target...Any deviation from the process will deliver different results....
    Randy