will a deeply seated bullet drop velocity?

Discussion in 'Reloading Forum (All Calibers)' started by Winny94, Sep 22, 2019.

  1. Winny94

    Winny94

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    I did the Berger VLD seating depth test and found a .090 jump was best in my rifle. I have a short freebore, so a .090 jump puts CBTO at 2.0425 (~2.800 COAL). I did my charge weight testing today and while I had some amazingly consistent and very accuraye loads, they were SLOOOWWW. About 75-100 fps slower than comparable loads from others shooting the same cartridge/barrel mfg/ bullet/powder/primer
    So my question is, would a stuffed bullet (it is very much in the powder column) reduce velocity even though the charge is the same as others that dramatically?
    If no, either my scale or Chrono is lying to me, or I just have a slow barrel.

    Details:
    7mm Sherman short
    Adg brass
    180gr Berger VLD hunting
    62.4 h1000 = 2835 fps ( es 8, SD 4.6)
    Compressed load, loaded with drop tube

    Note: I do plan to rework this load (or go with a 175gr Berger), but this load is going be the load for a mulie hunt next week, so I'm not looking for an overnight solution , just some thoughts from those more experienced than me.

    Thanks for any insight
     
  2. rammac

    rammac

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  3. Tim Singleton

    Tim Singleton Silver $$ Contributor

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    IME
    Bullets out of the lands take more powder to reach same velocity as a bullet engaged in the lands.
    Pressure thing
     
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  4. SPJ

    SPJ Gold $$ Contributor

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    Can ya hit what your aiming at ?
    Will it kill cleanly?
     
  5. rhovee

    rhovee

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    How close did you try the 180's? I would try 3-5 in, and 3-5 off. And no your not going to stick a bullet going 3-5 in the lands.
     
  6. MTlager

    MTlager Silver $$ Contributor

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    I have never been able to get much velocity from H1000 in the Saum. Running 3000 fps with RL 23 or 26.
     
  7. Prose

    Prose

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    Wrong. Seating near or into the lands can completely change the pressure curve. “Internal ballistics” is the study of this. A long jump, dependent on powder bullet chamber combo can cause a decrease.

    Just today I was shooting a 6.5 CM, seated into the lands at 2.878 with 42.9 H4350 netted me 2855 10 shot avg Sd10. Same load at 2.792 was 2760 Sd 5 10 shots each.

    Again, this will vary completely from one combo to the next.
     
  8. Winny94

    Winny94

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    Per Bergers advice, I got as close as .010". It wasn't fantastic (especially compared to the .090 range), but wasn't the worst. After I get back, I may give it a shot closer in. Mag length would put me right at ~.003" average jump. Can't jam and still fit in the mag.
     
  9. rammac

    rammac

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    No, I'm not wrong.

    The original poster didn't say anything about comparing to being in the lands, simply seating deeper will reduce the usable case volume which will increase the pressure which will increase the velocity. Yes, if you start from a jammed bullet there will be a reduction in velocity initially but as you keep seating deeper you will see the velocities go up again.

    I am well aware of what the science of internal ballistics is.
     
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  10. wedgy

    wedgy Gold $$ Contributor

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    Yes, that is a bit slow, what barrel length ? If you have an ES of 8 I'm guessing the chrono is MS or LR and probably isn't the issue. RL 26 will usually give the best velocity but has been shown unstable above ~84F but is very stable below that. It gets the barrel very hot if shooting strings but great in hunting rifles.
    How many rounds on the barrel ?
     
  11. mikecr

    mikecr

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    You don't know anybody else's seating relationships, so it seems like you're reaching this direction without basis. And rammac is right.

    You didn't say, so I wonder if this brass was new or fully fire formed at the time of offense.
    There may also be a chronograph issue that we could discover here.
    Type? Distance to muzzle? Time of day, lighting?
     
  12. Winny94

    Winny94

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    26" bbl. Chrono is a magneto. I was going to try RL26, but it has been scarce.
     
  13. Winny94

    Winny94

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    4th firing on the brass. 200 rds on the barrel now. Chrono is a magneto.
    FWIW, the others load that is nearly identical to mine is shooting a 20 thou jump and 90 fps faster.
     
  14. Bradu

    Bradu

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    Oit of curiosity, what is case capacity of the fire formed brass? Seating deeper will increase your pressure some, quickload is a good method for showing this. I'm leaning towards a slow barrel, I have that problem with my 6.5 saum. I hit pressure sooner than most and don't know how some of these guys get the speed they do. Rl26 is the ticket from the little experimenting that I've done but chances of finding it are slim.
     
  15. JimSC

    JimSC

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    from my testing using the Berger seating test I have found that from .120 jump to around .060 jump the velocity will decrease then from .060 to the lands the velocity increases. I have seen this happen several times now and it is easy enough to test on your own rifles
     
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  16. Winny94

    Winny94

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    Thanks - I have a dozen prepped cases left over so I loaded a quick ladder with a .005" jam (I mistakenly said earlier I couldn't jam at mag length, I had my math wrong). Planning on heading out over lunch tomorrow. Should be a quick test to tell.
     
  17. JimSC

    JimSC

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    That would be good, I would like to see if other rifles behave the same way. I went back and looked at my spreadsheets, which I should have done before posting, and found the majority behaved like the 6CM did but there was a anomaly or two. Berger 80's just got faster the closer they were to the lands until jam then for some reason they dropped 30 FPS. 77SMK's with Varget did the drop then climb routine yet Varget with 120 and 123 SMK's and Varget in a .260 Rem just climbed steadily the closer they got.

    this would be worth a more indepth study
     
  18. Laurie

    Laurie

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    Ignoring the effects of 'jammed' bullets which increase pressures considerably, for jumped set-ups there comes a point where deeper seating / increased jump produces an MV drop - but I've never heard of anything close to 100 fps.

    This factor is widely known and has been illustrated many times. For instance Vihtavuori / Lapua had a COAL v MV table many years ago for a standard military 7.62X51 Lapua load fired through a pressure barrel and results documented. Initial modest COAL reductions / larger jumps saw no change in MV / pressure, but at a given point both dropped - not huge amounts, but enough to be seen and was repeatable.

    I saw it myself recently doing COAL tuning in a 284 Win with the new Sierra 183gn MK over Viht N165. Starting with the bullet just touching the lands and then seating deeper in 10 thou steps, there was no MV change until 40 thou' jump was achieved when it dropped by 10 or 12 fps and stayed at the lower level for the next two COAL reductions at which point I stopped testing. This was on a single figure ES combination so a change is valid (measured on a Labradar in a single session with the barrel not allowed to get hot). In fact, the load was so 'single figure' that a mild 'in' COAL saw an ES of 1 from a five shot test batch - big shame it had an inch vertical stringing at 100 yards!
     
  19. Winny94

    Winny94

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    Well, anecdotal at best, but putting them at the lands gave me 60-65 FPS more for like charges
     
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