Jesse
Lv 5
Jesse asked in SportsOutdoor RecreationHunting · 1 month ago

Ballistics:Temperatures effect on muzzle velocity question?

The temperatures effect on a bullets muzzle velocity. Is that a constant?

If your FPS is for example 2750 FPS and your ammo temp. and ambient temp. are both 70deg F. At 60deg F or 80deg F is the increase or decrease in M.V. caused by the temp. on the ammunition always going to be a constant, not including other factors such as fouling and bore erosion?

Update:

I’m going to try and explain it better. Regardless of the heat in the action or barrel etc... Say you cold bore shot 2 shots. One at 70 deg F, let’s say your M.V. is 2750. Now let’s say you take a second shot at 80deg F. Both on a cold bore, both ambient and ammo temps match. The only difference is a 10 deg increase. That 10 deg increase will increase your muzzle velocity. 10 deg colder than 70 deg will reduce your MV. Because temp. effects MV. So is that difference a constant? 

7 Answers

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  • Robin
    Lv 7
    1 month ago

    the distance needs to be accountedfor. at 1200 yds the tempreture, velocity, humidity, air pressure would have all changed from the muzzle

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  • 1 month ago

    Cold air is denser. Denser air slows down the bullet more. Unless you are shooting very long range, it really does not matter. Cold also thickens up any liquid lube you use so either do not use it, use graphite, or wipe as much off as you can. You might also consider your powder if you reload. A clean burning powder is always best.

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  • BBean
    Lv 7
    1 month ago

    Kinda funny to me how some questions project mental pictures that only a movie scene can explain close to how I see them. The movie Wild Times where a buffalo hunter, being a phenomenal marksman, developed problems with an overheating barrel in a shooting contest that was playing havoc on accuracy. A defeated competitor offered helpful advice...dip the barrel in a bucket of water. Advice taken...accuracy restored. That advice was probably thought of as a secret "trick of the trade" in that time era. Doesn`t that correlate with your question?

    Of course, any change in temperature can affect everything concerned and one constant is 'no two things are perfectly(as in 100%) alike.'

     Can one imagine a barrel with thermocouples affixed every inch apart with individual gauges to read temperature differences and recording every shot through a chronometer? An instrument panel would resemble a cockpit in an airplane and really the most unhelpful information to rely on to compensate for more important inadequacies. Too much science can and has ruined several of my hobbies.

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  • Anonymous
    1 month ago

    Yes the barrel gets hot after you fire several bullets through it.

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  • 1 month ago

    I only must say Glacierwolf this time you SHOW your an inexperienced IDIOT. Possibly you missed Physics class or were not up to the qualifications for that either. I guess my and many others keeping their ammo in a cooler makes no sense on a hot day. Funny also we must calculate differently for the denser COLD air because of the increased drag.

    Only one more time you show you are in fact a phony.

    Also IN FACT on very cold days the barrel WILL contract and it expands slightly in heat. This is how you SOLIDLY attach two metal parts without welding. Put one in the freezer, insert it in the other part, and let it normalize in temperature and I guarantee you that will NEVER come apart unless you reverse the process. Heat the outside part until the center which is cooler can be removed.

    Simple physics if Glacierwolf had a clue.

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  • 1 month ago

    Guys, there is only so much room here to explain.

    First, when you leave your WARM car or HOUSE your barrel is not at ambient air temperature instantly.  I guess if you bungie cord it to the bumper....

    Second. At -45F you run out of your car, take a few shots, then get the heck back in.  Only an idiot would leave the weapon on the shooting bench since any exposed flesh that accidentally touches it will flash freeze.  

    Eielson AFB has heated winter shooting positions.  Big @ss heaters blowing at your back.  Your weapon is at 50-60F but once out the open door the bullet is at the mercy of ambient temperature.

    Slappit - air gets denser as it gets colder.  I do not know how you can argue with that. Somehow you must have read something wrong is all I can think of.  I have learned some good things from your posts - however - I think you are being overly harsh.  Whats up?

    As to the answer.  When I fire 10 rounds of factory ammo in a clean gun there will be deviations sometimes as high as 150fps between the faster round and the slowest.  I have a new Ruger 308 Predator, I have fired two 10rd strings as fast as possible through a chronograph with Winchester 168grBT ammo and got 2FPS difference!  I went back to the store, sure this was a fluke.  Bought another box and got the same only 3fps.  Other boxes did 30-50 fps and two did 100fps high to low.  My point - you will never get a bullet to fly the same speed as the next - air temperature would need to be hundreds of degrees difference to make any noticeable change in the variable already inherent in firearms because:

    No two bullets have the exact number of gunpowder ganuals.

    No two bullets are perfectly identical in length

    Very few bullets in a box or normal ammo have the same coaxial alignment.

    1. Ammunition temperature is not an issue. Barrel temperature is.  In a centerfire rifle after 5 quick shots the barrel can be hot enough to hurt your fingers. As the barrel warms up it expands.  The expansion makes the barrel rifling wider which  decreases the resistance between the projectile and barrel - the projectile will travel faster.  As a bullet travels from Point A to Point B faster gravity has less time to pull it earthward - it will almost always strike higher.  The effect was a cold barrel vs. hat barrel can be detected in as little as 100 yards.  This is why you see bench rest shooters fire one round, then wait a few minutes before firing the next.

    2. Air temperature is an issue.  As the air gets colder it become denser.  This will increase drag on the bullet from Point A to Point B.  Not really noticeable at short range - it becomes apparent at longer distances, beyond 200 yards.  Especially when hunting in open tundra during winter when shots can be quite long - this is something hunters need to factor in.

    3.  Altitude is an issue.  The higher one goes - the less air pressure - this will cause less friction of the projectile going from Point A to Point B.  Shots will go high since the reduced air friction does not slow down the projectile as it would at sea level.

    Something to consider.  Bullets traveling past the speed of sound, 1080fps at sea level, develop a vacuum behind that creates a ballistic crack.  This is also a consideration for an extreme long distance shooter.

    Hope this helps 

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  • 1 month ago

    I am going out on a limb to say that under most conditions the normal variances of muzzle velocity on commercial ammo will make much more difference in muzzle velocity than an air temp difference between 60 and 80 degrees. Besides, after the first shoot the temperatures inside the barrel are increasing anyway.  It iis 60 in the barrel bore on the first shot, it is probably 80 or more on the second shot.

    --Russ

    • falconry2
      Lv 7
      1 month agoReport

      As Russ says, if you're shooting factory ammo the difference from cartridge to cartridge (various factors) is going to affect velocity/accuracy more than minor temp changes. Going from 100* to -20* can effect some powders and will change air density but not enough for an average shooter to notice. 

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