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Effect of Altitude on Bullet Velocity

Discussion in 'Competition Shooting' started by 9mmepiphany, Sep 6, 2017.

  1. 9mmepiphany

    9mmepiphany Moderator

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    I live at 30' above sea level and will be shooting a match next weekend at 5800'.

    Will the difference in altitude have much effect of the velocity of my pistol ammo?

    I'm shooting a revolver loaded with .38Spl . 170gr coated bullet over 3.2grs of Clays. I'm getting a velocity around 680-700fps (120PF). The minimum velocity I need is about 620fps (105PF), but I'd really like to have at least 675fps (115PF) for a little cushion.

    Anyone ever run into a chronograph issue at higher altitudes?
     
  2. Klint Beastwood

    Klint Beastwood Member

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    The higher in elevation you go the thinner the air gets. Thinner the air gets, the less drag is on the bullet from the air density= the bullet will being going faster @ higher altitude.
    I live boarder to 3000ft. I've never had an issue with a chronograph. When the light sensor chronos where the only thing on the market...well i think everyone has issues with those...getting to much light in the sensor, not enough, on an angle, etc. However, no never had an issue related to elevation.
     
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  3. taliv

    taliv Moderator

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    9mm, i don't think you'll have an issue. i can't imagine what would cause a velocity loss unless your powder is extremely temp sensitive and your altitude change comes with a steep drop in temperature.
     
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  4. 9mmepiphany

    9mmepiphany Moderator

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    Thanks, this has been my thought process also.

    I think the MD was just messing with out-of-towners coming to the match with his Welcome email containing: "Please remember that Farmington sits at about 5800 ft. above sea level and that may affect how your ammo performs if you are coming from somewhere that has a vast difference in altitude"
     
  5. ny32182

    ny32182 Member

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    You may see a difference, but as mentioned, if all else is equal you will gain velocity rather than lose it.
     
  6. taliv

    taliv Moderator

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    that said, MY performance at altitude is noticeably different
     
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  7. Corpral_Agarn

    Corpral_Agarn Member

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    How far away are the targets?
     
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  8. Schwing

    Schwing Member

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    This wouldn't be Farmington Utah by any chance would it?
     
  9. Sam1911

    Sam1911 Moderator

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    It wouldn't be a matter of distance to the targets he's worried about, but rather velocity going over the chronograph.

    At many large IDPA or USPSA matches your ammo is tested to make sure it is running hot enough to clear the power limits, so they know you aren't gaming with light "powder puff" loads.

    He doesn't want to show up and be disqualified because his ammo ran slower than normal due to altitude.

    Having said that, I would expect it to be a bit faster, not slower.
     
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  10. tarosean

    tarosean Member

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    Farmington NM?
     
  11. Corpral_Agarn

    Corpral_Agarn Member

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    Ah. That makes sense.

    Thanks
     
  12. 1stmarine

    1stmarine Member

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    No practical difference unless temperature drops substantially with that altitude that is another factor associated with altitude and depending how sensitive the powder is to temp changes.
    I am afraid if temperature in fact drops, with clays and low density in pistol rounds you might experience changes in ignition and burn that in shotgun loads I don't see much loaded
    compressed shot-shells as intended for this powder.
    So find out about temperature forecasts and might want to use proper pistol powders for that round.
    In the air if you have a target at long distance then you have to consider that barometric pressure change but otherwise it is not a factor for average pistol shooting.
     
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  13. Berger.Fan222

    Berger.Fan222 Member

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    We've seen a small effect with rifle ammo (~50 fps), but the muzzle velocity always increases with altitude.

    A back of the envelope calculation was able to attribute the effect to the difference in the mass of the air in the barrel. Higher altitude -> less air in the barrel to push out. Less air in the barrel -> more bullet velocity when it leaves.

    I expect that the effect would be much smaller in pistol barrels than in 22-30" rifle barrels.
     
  14. 9mmepiphany

    9mmepiphany Moderator

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    I've been giving this a lot more thought also.

    Taking Iron, heavily hydrating, and loading carbs before the match
     
  15. 9mmepiphany

    9mmepiphany Moderator

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    Farmington, New Mexico. They say the new Fairfield Inn and Suites is very nice
     
  16. papaairbear

    papaairbear Member

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    With thinner air creating less resistance to the bullets energy-or lower drag- wouldn't the bullet strike the target a bit higher, depending on the range? Inconsequential difference probably, but maybe not?
     
  17. 9mmepiphany

    9mmepiphany Moderator

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    Yup, it isn't even the entry fee that would bother me, but traveling 16 hours and not being able to shoot the match

    When your required PF is only 105 (618fps), it is pretty hard to "game"... and still have any margin to reliably take down steel. I usually load to about 115PF (675fps)...which surprisingly chrono'ed out to 120PF in Seattle last month
     
  18. tarosean

    tarosean Member

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    It's a hotel, I've stayed in it. ( very few hotels around the world impress me)

    make sure you take in the local Mexican restaurants and green chili. no chain restaurants!
    Green chili cheeseburger is heaven on a bun!
    ( I grew up close to there.)
     
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  19. 9mmepiphany

    9mmepiphany Moderator

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    I welcome eatery suggestions.

    We'll be having dinner Friday after we arrive, and get chrono'd, and an aftermatch dinner Saturday night. I love going to the places that locals frequent
     
  20. Klint Beastwood

    Klint Beastwood Member

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    well...that makes a bit more difference with rifles at further distance and the velocity change with a new DA. The difference at 25ft and with a handgun not so much....
     
  21. climbnjump

    climbnjump Member

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    Um, doing those 3 things right before a match might not be a good idea, so I'm assuming you're spreading them out. If you're driving from CA to NM, then your body is starting to adjust as you drive higher. Oddly enough, the same applies if you're flying as cabin altitudes are usually kept at a pressure equivalent to around 8000 ft, but the exposure time is less. Heavily hydrating the day before is probably a good idea, as is avoiding alcohol. The iron tabs aren't going to really do anything for you except perhaps upset your stomach - some people are sensitive and some are not. If you normally load carbs before competing at a match at your normal altitudes, then go for it. If you are doing it special for this match, it might not be wise - lower oxygen levels do adversely affect digestion, although 5800 ft probably isn't high enough to affect most people if they eat within reason, so just do what you normally do.

    If you do have spare time the day prior to the match, then you might take a leisurely hike up to a higher altitude (than 5800) and spend a few hours there. Going higher will help cue in your body to adjust. Then get a good night's sleep. During the match, remember to concentrate on your breathing. When you are between stages, breath deeply then exhale with pursed lips as though you are blowing out candles on a birthday cake. This raises the pressure in your lungs which helps increase oxygen absorption across the alveoli into your bloodstream. This is called "pressure breathing" and is a standard mountaineering "trick".

    Enjoy the match!
     
  22. 9mmepiphany

    9mmepiphany Moderator

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    That is defiantly on my list...I learned it when shooting 3-position rifle back in high school.

    Thanks for the tips on the other things. I do usually carb up, but not heavily, hydrating is what I have to keep reminding myself to do. What I'm really looking forward to are temperatures well below the 106 at my last local match
     
  23. tarosean

    tarosean Member

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    Mexican
    Dona Maria
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    Si Senor

    Fast food burger = Blakes Lotoburger.
    Clancys Irish pub = pub food.


    * I have not been there in about 5yrs and the oil crash devastated the 4 corners region, so a lot could have changed..
     
  24. murf

    murf Member

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    suggest you walk as much as possible to acclimate yourself to the altitude. flatlanders become exhausted quickly at altitude until they spend enough time in the high country.

    luck,

    murf
     
  25. 9mmepiphany

    9mmepiphany Moderator

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    Thanks for all the advice.

    Turns out it was never an issue, the ammo chrono'd a bit hot; I didn't even do much gasping...must have been the 16 hours in the car getting there through higher elevations .

    The runs in IDPA are pretty short and these stages were overall pretty short...with 13 in one day, I would have expected them to be

    Won my Class, came in 2nd in the Division (loss of focus on a stage)
     
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