close

Privacy guaranteed - Your email is not shared with anyone.

Help me finish learning something new

Discussion in 'Reloading' started by Schrag4, Mar 18, 2017.

  1. Schrag4

    Schrag4

    Joined:
    May 21, 2010
    Messages:
    1,700
    Likes Received:
    621
    Location:
    Wichita, KS
    Today I tested a new bullet- powder- gun combo. 115gr FMJ (9mm) and AA#5 5.6gr out of an 8.3 inch barrel. I loaded up all 25 rounds in the ETS Glock mag and shot them over a chrono without much time between shots. I had a camera rolling on the chrono so I wouldn't have to stop to write anything down.

    Well, the first 10 or so rounds were very close together in velocity, but then they tended upward, and the last 10 or so ended up close together too, but about 35 FPS higher than the first group.

    What can explain this? Without having looked anything up, I think it must be either a hotter chamber causing the powder to burn faster, more completely, or the inside bore diameter changing due to expansion.

    Your thoughts?
     
  2. Schrag4

    Schrag4

    Joined:
    May 21, 2010
    Messages:
    1,700
    Likes Received:
    621
    Location:
    Wichita, KS
    ETA - just looked at the data again and the first 10 had an avg of 1362 with a stdev of 5.3 and the last 10 had an avg of 1396 with a stdev of 9.2
     

  3. Kwesi

    Kwesi

    Joined:
    Sep 23, 2006
    Messages:
    1,735
    Likes Received:
    62
    Location:
    TX
    How are you weighing your charges? Are you using check weights first? What scale are you using? Most good scales are accurate within .1 gr. so that could account for it.
     
  4. Schrag4

    Schrag4

    Joined:
    May 21, 2010
    Messages:
    1,700
    Likes Received:
    621
    Location:
    Wichita, KS
    I don't weigh every charge, just the first few. I don't see how the scale is relevant as it doesn't throw the charge. My powder measure is the Lee Pro Auto Disk, the $15 upgrade to the LCT kit at Kempf Gun Shop.

    Do you seriously weigh every single charge and throw back any outside of a certain tolerance? I could see doing that for precision rifle, but IMO it makes no sense whatsoever for general plinking pistol ammo.
     
    happie2shoot likes this.
  5. sig357fan

    sig357fan

    Joined:
    Apr 8, 2008
    Messages:
    1,030
    Likes Received:
    126
    Location:
    SW OH
    Schrag4,

    is the increase in velocity linier, meaning a noticeable "climb" in velocity as each round was fired in a progressively hotter chamber.

    sig357fan
     
  6. sig357fan

    sig357fan

    Joined:
    Apr 8, 2008
    Messages:
    1,030
    Likes Received:
    126
    Location:
    SW OH
    Scharg4,

    another question, where any of the velocities the "expected" velocity for the load you were developing.

    sig357fan
     
  7. Kwesi

    Kwesi

    Joined:
    Sep 23, 2006
    Messages:
    1,735
    Likes Received:
    62
    Location:
    TX
    Schrag4: I only weigh every charge when working near max/hot loads. I load on a Dillon 550 & not familiar with your equipment. The scale is the way to confirm your grains however you drop the powder. A set of check weights is how you know if your scale is weighing correctly.

    I believe any of the experienced loaders would throw 10 & weigh each to confirm.
     
    orangejeep06 likes this.
  8. Schrag4

    Schrag4

    Joined:
    May 21, 2010
    Messages:
    1,700
    Likes Received:
    621
    Location:
    Wichita, KS
    I suppose it wasn't a smooth climb.

    upload_2017-3-18_17-28-1.png

    Load data states it's from a 4" barrel. This is 8.3" I didn't know what to expect, but mid 1300s doesn't sound unreasonable.

    It sounds like the only feedback so far suggests inconsistent throws from my measure. I will try to weigh charges more often to confirm consistency. I don't know what I would do, though, if I saw an increase or decrease of, say, 0.2 or 0.3 gr. I'm using the disks so that kind of change would be smaller than if I moved to a bigger or smaller cavity. Of course if I'm loading near max then that's a different story. In this instance, I used the same prescribed OAL and the prescribed min/max are 5.3/6.3, so I'm still closer to the low end.
     
  9. willie_pete

    willie_pete NRA Life Member

    Joined:
    Sep 11, 2000
    Messages:
    11,088
    Likes Received:
    9,194
    Location:
    Sunny Fla
    Something defintely changed after the 11th round. There is a step change in average vel. after the 11th round. Were they shot in the order they were loaded? If so, look at powder charge changing for some reason. If they were mixed, look for something else; It doesn't look like barrel heating on that graph with the step change.

    wp
     
  10. Dave514

    Dave514

    Joined:
    Jul 6, 2013
    Messages:
    27,300
    Likes Received:
    9,342
    Location:
    USSA
    I'd say a powder difference due to the step up but a barrel heating up and being fouled will often result in greater velocities.
     
    fredj338 likes this.
  11. crockett

    crockett

    Joined:
    Mar 26, 2010
    Messages:
    5,587
    Likes Received:
    5,974
    Higher temp in barrel expands the outside diameter, but also tightens the inside. Tighter barrel = higher velocity.
     
    fredj338 likes this.
  12. sig357fan

    sig357fan

    Joined:
    Apr 8, 2008
    Messages:
    1,030
    Likes Received:
    126
    Location:
    SW OH
    schrag4,

    anything left in the barrel, progressive build up of soft jacket metal?

    the reason I ask is when trying to work up a cast bullet load in a G31 in 357 Sig I saw lead build up in the first 2 mag fulls, granted, I was using a cast bullet but if you got a bad batch of bullets with soft jacket material, could it build up in that few of rounds enough to cause pressure/velocities to increase.

    sig357fan
     
  13. fredj338

    fredj338

    Joined:
    Dec 22, 2004
    Messages:
    24,044
    Likes Received:
    2,581
    Location:
    so.cal.
    Crockett & dave nailed it, barrel/chamber temps. Allow 1min per ahot & see your chart looks like.
     
  14. sciolist

    sciolist

    Joined:
    Nov 11, 2009
    Messages:
    5,841
    Likes Received:
    3,326
    Location:
    PNW
    Really? I've noticed this to a much lesser degree, and wondered about the effect of internal temperature. Will have to try it next time I do chrony. I've definitely never waited anywhere near a minute between shots.
     
  15. fredj338

    fredj338

    Joined:
    Dec 22, 2004
    Messages:
    24,044
    Likes Received:
    2,581
    Location:
    so.cal.
    Also depends on the powder. I see it a lot when doing rifle testing.
     
  16. jmorris

    jmorris

    Joined:
    Apr 13, 2006
    Messages:
    2,010
    Likes Received:
    484
    Try firing two shots in a row, then lower the muzzle, then raise and fire another, then point the barrel into the sky and lower to fire through the chronograph.

    The last shot is likely to be the fastest.

    Also. You didn't say what chronograph you have but it can also depend on where through the screens you are firing as to what they read.
     
  17. sciolist

    sciolist

    Joined:
    Nov 11, 2009
    Messages:
    5,841
    Likes Received:
    3,326
    Location:
    PNW
    Thanks. I'm going to have to experiment with this.
     
  18. BWC45ACP

    BWC45ACP

    Joined:
    Mar 4, 2016
    Messages:
    37
    Likes Received:
    22
    Location:
    Kentucky
    Powder gets a little dense in some powder measures due to vibration or shaking around while reloading.Making the charge weight increase. Before I started using a Dillon I would tap on the bowel of the measure to make sure the powder had settled. Never had any problems after that
     
  19. fredj338

    fredj338

    Joined:
    Dec 22, 2004
    Messages:
    24,044
    Likes Received:
    2,581
    Location:
    so.cal.
    If I stop for more than a couple minutes, I throw a couple charges back before getting back to the reloading process. Yes powder does settle in the measure.
     
    happie2shoot likes this.
  20. WeeWilly

    WeeWilly

    Joined:
    Nov 12, 2011
    Messages:
    6,493
    Likes Received:
    3,464
    Location:
    Idaho
    I have to be honest, I think your results were random, they just happened to land that way.

    Every time I am out at the range and testing handgun loads, I will think I see a pattern, maybe velocity climbing as I am shooting multiple sets of the same flight. Just when I think I have it figured out, another pattern emerges.

    Now, I just look and look and see a larger ES than I was hoping for.. ;)