Velocity and temperature

[getitdone1]

Just finished reading the "cold weather" thread. Got me to wondering how much temperature effects muzzle velocity. I know it does.

Anyone have some numbers?

Don McCullough

[jdad]

W748 is extremely temperature sensitive. One of the shooters, in our silhouette league, has sight settings for 30, 60, and 90 degrees F. He says that his load MV will vary as much as 150 fps, from the extremes.

I know that the Vhita Vouri powders are the least temp sensitive, but they are hard to find and have become quite pricey.

[Griff]

Physics ain't a strong suit of mine... since for all intents and purposes I flunked chemistry... but strictly as a mental exercise, I've often wondered... just in what direction does a round object, with a hole down the middle of it, contract due to the cold?

Is the "hole" smaller or larger?

[J Miller]

W748 is extremely temperature sensitive. One of the shooters, in our silhouette league, has sight settings for 30, 60, and 90 degrees F. He says that his load MV will vary as much as 150 fps, from the extremes.

I know that the Vhita Vouri powders are the least temp sensitive, but they are hard to find and have become quite pricey.

I don't doubt there's some variation, but 150fps? Wow!

I've been shooting 748 for decades and never noticed any such changes in point of impact.

I'm wondering if the different layers of clothes the shooter would be wearing at the different temps is changing his hold, therefore changing his point of impact? Just a thought.

Joe

[Old Savage]

You are clealry a theoretical physicist/philosopher.

[86er]

The temperature issue starts with the deterrent that is on the powder. Deterrent, for those that don't know, is a coating put on the powder to adjust the burn rate. Some powders are "double deterrent" powders. That is, they have two different coatings to adjust the burn rate. One coating burns or "melts" off before the next coating is affected. Then the actual "powder" ignites. The deterrents are compounded mixtures. These mixtures have different "melting points". The melting point of the deterrent is expressed in degrees of ignition temperature per standard environmental temperature, for instance 1400 degrees at 72 degrees. When the environmental temperature changes greatly from the standard, the deterrent takes more or less time to melt. For cold, it would take longer. In super-slow motion what happens is the force of the primer pushes the bullet forward a little before the powder begins to burn. This has already dropped the case pressure a little since there is now more room in it. Next, the powder deterrents react and eventually the powder burns. At this point, some of the powder may not be burning in the case but rather in the barrel. Again, this reduces the pressure build up in the case and subsequently changes velocity. I find it interesting that extreme heat can reduce velocity too. Cordite is a good example. In the case of too much heat, the deterrent is already entering a "molten" state. First, it no longer evenly coats all the powder and second it virtually disappears at a lower temperature than was intended. Here, the immediate ignition of the powder pushes the bullet forward before enough pressure builds up in the case, possibly with some powder still burning while it enters the barrel. The cartridge loses pressure and thereby velocity. With different powders, heat can increase velocity. If the deterrent is loose from the environmental temperature, certain powders will burn faster than intended and quickly build pressure entirely in the case before the bullet moves forward. This instantaneous and complete burn increases velocity. Whether increase or decrease in velocity, the three factors are environmental temperature, ignition temperature and rate of deterrent(s). In extreme instances, I have seen a 450 N.E. with Cordite that shot 2150 fps at 72 degree environmental temperture push the same bullet just 1900 fps in 116 degree environmental temperature. I also had a decrease of 200 fps with an Alliant powder in 109 degrees, where a load with the same MV that was pushed by H4350 actually gained 95 fps on the same day.

[pwl44m]

HUH ! Good Post Joe I actually imagined Myself climbing inside the Case watching all this happen. Ambient temperature has its affects on a lot of things (most over My head).
@ Griff, it aint "larger" It's "Bigger" lol

[AJMD429]

Physics ain't a strong suit of mine... since for all intents and purposes I flunked chemistry... but strictly as a mental exercise, I've often wondered... just in what direction does a round object, with a hole down the middle of it, contract due to the cold?

Is the "hole" smaller or larger?

Interesting question - at first it seems 'obvious' that the hole would shrink when the temperature goes down, as the overall dimensions of the metal would shrink, and obviously the external diameter of the barrel would shrink. BUT the thickness of the barrel wall would shrink as well, so that would tend to open up the bore. However if you think of it in terms of the circumferences (external and internal), would they both not have to shrink?

I guess the bullet would shrink, as well, in cold temperatures, although I'll bet it's temperature upon muzzle exit is pretty high regardless.

[handirifle]

WOW! 86er, I am impressed. I learned more in the (won't tell you how long it took) time to read that than I have in a lot of years reading articles on powders.

This double coating, is that what they're referring to in a "double based" powder?
Thanks

[86er]

Thanks - actually the deterrent is the coating on the powder, and double deterrent is two layers of different coating. The base is the amount of solid product that converts to gas expressed in a percentage of nitro (cellulose, glycerin or guanadine). The "double base" is a powder formula or (rarely) a powder kernel that is formed from solids with two different percentages of nitro. The deterrents are centrilytes like diethyl, dimethyl or dibutyl phthalate. There are other contents that do not effect the burn rates. They are stabilizers and additives. Additives may be a potassium derivative, commonly used for flash suppression. Also, surfactants are used to make spherical powder, hold grain shape and prevent sticking and static electricity.

[RKrodle]

Physics ain't a strong suit of mine... since for all intents and purposes I flunked chemistry... but strictly as a mental exercise, I've often wondered... just in what direction does a round object, with a hole down the middle of it, contract due to the cold?

Is the "hole" smaller or larger?

Smaller. Like installing bearings on a shaft that is a tight fit. Heat the bearing and it expands and slides onto the shaft, or freeze the shaft and it contracts and the bearing slides on the shaft or a combination of the two.

[pwl44m]

Or heat a head and freeze a seat.

[Old Savage]

From my chronographing I think that 150 fps difference is easily possible.

[BigSky56]

Don I was down in Dillon this year for elk the temp was 0 and wind chill dropped it to 20 below I tried a shot at a target with my 348 loaded with IMR 4895 the bullet hit 2' low at 200 yds I tried a shot with AA4350 it dropped maybe 16"-18" I dont like chasing wounded elk since then I have been working on a load using RE-17 as it is a 4350 type powder with more speed and the deterrent is combined through out the powder, as in no coating to burn thru, it is a extreme temp powder. I will have it up and going this spring. Up close and personal it wouldnt matter but at distance it makes a difference. danny

[Griff]

Physics ain't a strong suit of mine... since for all intents and purposes I flunked chemistry... but strictly as a mental exercise, I've often wondered... just in what direction does a round object, with a hole down the middle of it, contract due to the cold?
Is the "hole" smaller or larger?

Smaller. Like installing bearings on a shaft that is a tight fit. Heat the bearing and it expands and slides onto the shaft, or freeze the shaft and it contracts and the bearing slides on the shaft or a combination of the two.

Oh gee... just take the mystery out of my favorite musing subject!!!

[alnitak]

Physics ain't a strong suit of mine... since for all intents and purposes I flunked chemistry... but strictly as a mental exercise, I've often wondered... just in what direction does a round object, with a hole down the middle of it, contract due to the cold?

Is the "hole" smaller or larger?

Might it not contract in both directions??

[RKrodle]

Physics ain't a strong suit of mine... since for all intents and purposes I flunked chemistry... but strictly as a mental exercise, I've often wondered... just in what direction does a round object, with a hole down the middle of it, contract due to the cold?

Is the "hole" smaller or larger?

Might it not contract in both directions??

Maybe this will help.
http://hyperphysics.phy-astr.gsu.edu/hb ... hexp2.html

[vancelw]

Physics ain't a strong suit of mine... since for all intents and purposes I flunked chemistry... but strictly as a mental exercise, I've often wondered... just in what direction does a round object, with a hole down the middle of it, contract due to the cold?

Is the "hole" smaller or larger?

Might it not contract in both directions??

Maybe this will help.
http://hyperphysics.phy-astr.gsu.edu/hb ... hexp2.html

Smart aleck! There you go obscuring fiction with facts. Spoil all the fun.

Why does everyone have cold on their mind?

[getitdone1]

What motivated my temperature question is how it's gonna effect my shooting through milk jugs filled with water? Will a real cold day slow the bullet to where I'd penetrate one less jug--for example. I also wondered about the change in the water on a cold day--of course before it froze. For instance, would water a couple of degrees above freezing be harder to penetrate than water at 70 degrees? When you combine the two then perhaps even fewer jugs penetrated.

Then, what about the cold constricting the bore which would lower velocity?

May sound like I'm being overly picky but when you go to considerable effort, using many loads and bottles, you like to have accurate results.

Of course I can wait for this danged winter to be over with and then continue with my jug penetration tests but may be moving before good weather gets here. Have to finish the testing here.

Actually looks like 40-50 degree days will be here soon so I'm finishing my jug penetration tests then and know it'll be accurate enough.

Full report in a few days. 375 H&H going for 20 plastic milk jugs filled with water. FMJ 300 gr Hornady bullet. Penetrated 15 so far. Most soft nose bullets from centerfire ctgs go through 4-5 jugs. Fast, fragile varmit bullets only penetrate 1-2 jugs. Helps give you an idea of how dangerous it is to use fragile, poor penetrating bullets on large, dangerous game.

Don McCullough

[SJPrice]

Don I was down in Dillon this year for elk the temp was 0 and wind chill dropped it to 20 below I tried a shot at a target with my 348 loaded with IMR 4895 the bullet hit 2' low at 200 yds I tried a shot with AA4350 it dropped maybe 16"-18" I dont like chasing wounded elk since then I have been working on a load using RE-17 as it is a 4350 type powder with more speed and the deterrent is combined through out the powder, as in no coating to burn thru, it is a extreme temp powder. I will have it up and going this spring. Up close and personal it wouldnt matter but at distance it makes a difference. danny

I for one would be very interested in your progress and success.

[AJMD429]

Then, what about the cold constricting the bore which would lower velocity?

I KNOW this is a theoretical question . . . but . . . all else being equal (which of course it wouldn't be), wouldn't the smaller bore tend to increase velocity...?

It's kind of interesting to see how the "jug penetration" tests posted a few years back showed the .50 BMG FMJ loads penetrated far fewer jugs than a .45-70 heavy-bullet load plodding along at 1,000 fps or so.

[Old Time Hunter]

This is why I use the Hogdon Extreme powders like H4198 and H4895 instead of the IMR versions. They are coated differently.

[El Chivo]

I found a big difference in the heat with SR 4759, so I too switched to extreme powders. For pistol powder I use IMR 4227 since I called Hojjdon and they told me it was, for all intents and porpoises, an extreme powder as well.

For the question about the bore, cold metal will make a bore larger. The metal shrinks towards its center, away from the bore.

The reverse happens in hot weather, the metal expands outward, making the bore smaller.

bore.jpg

in this sketch, the dotted ring is the center of the metal, the metal expands or contracts towards this center. Metal expands, bore gets smaller. Metal contracts, bore gets bigger.

[Griff]

I've always been led to believe that a HOT bore will be smaller than a cold one. Metal expands in all directions... a cold bore will give less pressure than a hot one.

[getitdone1]

Lots of knowledgeable people in this group. I know I'm not the only one to notice this. Lots of "been there done that" guys here.

A good, knowledgeable leader helps and Hobie's the man.

Thanks for all the info.

Don

[Gobblerforge]

When setting the pin into a pintal hinge, the Blacksmith will heat the hinge with the eye in it. The pin is tapped into the eye and the hinge is cooled in the slack tub thus making the hinge smaller and locking the pin tightly. The hole gets smaller. The same is done to make large, hollow, light weight metal rollers. The tube is heated and the end inserted. The tube cools and locks it in. And I mean in. Don't get it wrong.
Gobbler

[Boreman]

86er,
An excellent and informative discussionon on the effect of temperature on
powder burn rates and their composition.
I think you should expand the information in an article with other powder data to be included as stickey for future reference.

[claybob86]

I found a big difference in the heat with SR 4759, so I too switched to extreme powders. For pistol powder I use IMR 4227 since I called Hojjdon and they told me it was, for all intents and porpoises, an extreme powder as well.

For the question about the bore, cold metal will make a bore larger. The metal shrinks towards its center, away from the bore.

The reverse happens in hot weather, the metal expands outward, making the bore smaller.

bore.jpg

in this sketch, the dotted ring is the center of the metal, the metal expands or contracts towards this center. Metal expands, bore gets smaller. Metal contracts, bore gets bigger.

What about the expansion and contraction around the circumference? Lot more metal there to react than just across the wall thickness. Somebody mentioned heating bearings to expand them to go onto a shaft. I know this is true from experience. Just sayin'.

[El Chivo]

we've long had the same discussion on the clarinet forum. A lot of people were mystified as to why a clarinet's pitch drops when cold and rises as you warm it up (a smaller bore makes the pitch rise). But it's because it's bigger, due to the shrinking walls.

One more example is a person who gets stung by a bee in the esophagus, they can suffocate because the throat swells shut. It doesn't swell open.

I think I know what you're describing, as if the shrinkage takes place around the circumference. Sort of like a hose clamp, as you tighten it, changing the length of the circumference. However, there's nothing pulling on the surface of your gun barrel. What you should think of is more like bread dough rising. It expands or shrinks in all directions.

If your barrel thickness is 5mm, and it shrinks to 4mm, that will leave 1/2mm extra space in the bore and 1/2mm less diameter on the outside. There's no reason for it to constrict like a hose clamp or a sphincter muscle unless it's being held in by something else.

[Griff]

I found a big difference in the heat with SR 4759, so I too switched to extreme powders. For pistol powder I use IMR 4227 since I called Hojjdon and they told me it was, for all intents and porpoises, an extreme powder as well.
For the question about the bore, cold metal will make a bore larger. The metal shrinks towards its center, away from the bore.
The reverse happens in hot weather, the metal expands outward, making the bore smaller.

bore.jpg

in this sketch, the dotted ring is the center of the metal, the metal expands or contracts towards this center. Metal expands, bore gets smaller. Metal contracts, bore gets bigger.

What about the expansion and contraction around the circumference? Lot more metal there to react than just across the wall thickness. Somebody mentioned heating bearings to expand them to go onto a shaft. I know this is true from experience. Just sayin'.

Do you know the thing they say about things you learn in your youth. "They will stick with you forever, and are harder'n all get out to unlearn." Thus is my example, well... maybe not that exact wording, but you get the picture!

Whence my dilemna, every time I think about this, this ONE thing I was told as young sailor sticks with me and makes me forget everything I've learned since. Why do shells get stuck in HOT bores? Our forward (& only) gun crew practiced getting its barrel cooled so that a stuck shell could hopefully come out before it exploded in the bore. Is there a point at which that expansion of ALL the metal in one direction (outward) becomes in all directions?

If you have a tight outer bearing race to go into the hub say, you freeze it to contract and it'll slip right in without beating... now, does the inner diameter of that race get smaller or larger? That was the point of my question.

I'm off to a shooting match... woo hoo!!! the weekend off, and the heck with chores! Ya'll discuss this and have an answer by this evening... or not!

[Gobblerforge]

On a bearing race, the cold makes the metal shrink. Both in thicknes and length. By this we can see that since there is a lot more length than thicknes the bearing race will be smaller in diameter. The same principal applies to wheelrights that have to set a buggy tire. The outside of the wooden wheel is measured. That length of metal is used minus just a little bit, Maybe an 1/8 to 1/4 inch. The weld is made to make the tire round and solid. Then the whole tire is heated in a round ring fire to expand the iron. I am told that up to 1/8 inch can be achieved per foot or so of stock. The tire is placed over the wheel and cooled to contract to iron and make a tight tire. Yes the metal gets thicker with the heat but it is made up for by the length of the stock.
Gobbler

[RKrodle]

On a bearing race, the cold makes the metal shrink. Both in thicknes and length. By this we can see that since there is a lot more length than thicknes the bearing race will be smaller in diameter. The same principal applies to wheelrights that have to set a buggy tire. The outside of the wooden wheel is measured. That length of metal is used minus just a little bit, Maybe an 1/8 to 1/4 inch. The weld is made to make the tire round and solid. Then the whole tire is heated in a round ring fire to expand the iron. I am told that up to 1/8 inch can be achieved per foot or so of stock. The tire is placed over the wheel and cooled to contract to iron and make a tight tire. Yes the metal gets thicker with the heat but it is made up for by the length of the stock.
Gobbler

Great example Gobbler. If I can find the right chunk of metal today I'll crank up my torch and break out my calipers and see about some pics and examples.

Griff, the round stuck in the chamber is from the cooler round being inserted into a hot chamber and then expanding as it sinks the heat from the walls of the chamber. The brass, if it's brass, has a different temperature coefficient than the steel chamber and will expand larger. Also depending on the difference of the thickness, difference between OD and ID or also referred to as cross section, the chamber may be real hot but has not expanded much. After all, the round did not become stuck until after it was inserted in to the chamber. Something had to chance from before and during insertion for it not to come back out. and that would be the temp of the round.

[rogn]

The hole in metal such as a hole in a washer expand and contracts linearly just as a sold mass of the same material. So, If you have a 1/2" hole in a metal plate or in a tube(barrel) The hole will behave exactly as a solid bar measuring the same 1/2";coefficient of expansion will be the same. This was explained above as the standard prceedure to place a "press fit" or "shrink fit" bearing on a shaft. As far as predicting velocity changes due to bullet and barrel dimentional changes, there are entirely too many variables to make any predictions, except probable change.

[El Chivo]

On a bearing race, the cold makes the metal shrink. Both in thicknes and length. By this we can see that since there is a lot more length than thicknes the bearing race will be smaller in diameter. The same principal applies to wheelrights that have to set a buggy tire. The outside of the wooden wheel is measured. That length of metal is used minus just a little bit, Maybe an 1/8 to 1/4 inch. The weld is made to make the tire round and solid. Then the whole tire is heated in a round ring fire to expand the iron. I am told that up to 1/8 inch can be achieved per foot or so of stock. The tire is placed over the wheel and cooled to contract to iron and make a tight tire. Yes the metal gets thicker with the heat but it is made up for by the length of the stock.
Gobbler

that sounds right - same principle as a Weaver scope ring. Because there is more length than thickness, expansion would loosen it rather than tighten it. But you're talking about a metal strap rather than a block of metal.

But, once it's tightened, aren't you more likely to have a loose scope in the cold rather than in the heat?

About the stuck artillery shell, I think that proves the bore shrinks. Sure the brass gets heated and expands, but if the bore was expanding too, it wouldn't get stuck. Or it would be less sticky with a hot bore because of the expansion. And the hotter it gets, the looser it should get. But the reverse is true.

One thing interesting about shooting is the interior of the bore gets hotter than the exterior of the barrel. So, on a cold day, if you shoot a lot, with the outer surface of the metal below freezing and contracting, and the inner surface very hot and expanding, what happens to the bore? It has to expand inward.

I have also wondered why your car engine runs better when it's warm. Is it because the parts are fitting together more tightly?

[Gobblerforge]

"One thing interesting about shooting is the interior of the bore gets hotter than the exterior of the barrel. So, on a cold day, if you shoot a lot, with the outer surface of the metal below freezing and contracting, and the inner surface very hot and expanding, what happens to the bore? It has to expand inward."

Naw man, the inside just gets bigger than the outside.
Gobbler