major general julian s. hatcher knew a thing or three about firearms and ballistics, gained over a long career in the united states military, at various times being in charge of the production of military ammunition at frankford arsenal, and also commanding various elements of the springfield armory which produced infantry arms for the united states.
his book, "hatcher's notebook," most recently published by the national rifle association, by odysseus editions, inc., is considered a must have and an authoritative comment on such matters as above.
and, for good reason.
the following is taken from chapter xvii, "random notes on various subjects," subpart 13, distribution of the heat energy of powder, page 399 of the above edition.--
"each pound of modern single base smokeless powder has a potential energy of about 1,250,000 foot pounds. if this powder is fired in a .30 caliber rifle, it will supply charges for about 140 cartridges, and each will fire a 150 grain bullet at 2800 feet per second muzzle velocity, with a muzzle energy of 2612 foot-pounds.
"the amount of this powder potential that has appeared in the form of muzzle energy of the bullets is therefore 140 x 2612, or 365,680 foot-pounds, or only about 29 1/4 percent. [the bullets, in other words, have only absorbed about that percentage of the potential energy of the powder upon its ignition. jjjay.] where did the other 70 3/4 percent go to?
"in 1929 the ordnance department set up a technical staff test program to determine this. the firing was done in a browning machine rifle, with results as follows:
"heat distribution of one round in a browning machine rifle.
heat to cartridge case ................................................ 131.0 b.t.u.
to kinetic energy of bullet ............................................ 885.3 b.t.u.
to kinetic energy of gases ............................................ 569.1 b.t.u.
heat to barrel .......................................................... 679.9 b.t.u.
total 2,864.0 b.t.u.
heat generated by friction ........................................... 212.0 b.t.u.
it is obvious from this that were some methods developed which would enable the bullet to absorb more energy, say from a very obvious source such as the remaining kinetic energy in the propellant gases which emerge from the barrel following the bullet in the form of incandescent heat and flame, that the bullet could be made to go much faster: one obvious way to do this would be to extend the length of a barrel so by the time they exited the barrel they would have given more energy up to the bullet. but, look at the figures, ... , if you extend the barrel, it is going to absorb just that much more heat from the energy in the propellant gases, to the detriment of the bullet's velocity.
and, so it goes.
i am developing a load for a rifle, a 7mm remington magnum shooting a 130 grain sierra matchking bullet, the end design/result which will be to propel the bullet a little over 3,000 feet per second from the muzzle. right now, at the early stages of developing this load, i am using about 60 grains of hodgdon h-4350 powder. 440 grains equals an ounce. 60 grains of this particular powder is just a little less than the volume of one teaspoon of powder. in other words, looking at hatcher's analysis, approximately 1/3 of the energy in this powder is propelling the bullet at over 3,000 feet per second from the barrel, while the rifle barrel, the weight of the propellant plus the heat energy it has been converted to is going out the end of the barrel without being utilized.
now, if you have a chance, sometime, stand by someone discharging a rifle, and from a position of absolute safety, grasp the barrel about midway when the rifle is shot. you can feel the heat of the cartridge's discharge migrate up the barrel from the chamber area, as its energy flows toward the muzzle.
this brings up an interesting topic, and that is how fast this sort of energy transfer, and containment of energy, will wear out a barrel. well, as a matter of fact, a rifle barrel gets eaten alive by the erosive and cutting effect of modern propellants very quickly: it is just that you don't notice it.
a high velocity rifle bullet will exit a rifle barrel in roughly 1/1,000's to 1/1,500's of a second. a rifle barrel is good for firing in competition for say, 2,000 to 2,500 rounds, before the rifling becomes so eroded in the barrels throat that the accuracy of the barrel degenerates so as to render it of no more utility for shooting targets.
just suppose if you fired it for 10,000 rounds the damage that the very hot powder flame/column would do to the interior of a barrel. well, it would chew it up.
10,000 rounds divided by 1/1000's of a second means that a cumulative time of 10 seconds is enough to destroy a barrel. think about it. it still sounds ridiculous, doesn't it.
if you still think it is ridiculous, talk to a military veteran who was a machine gunner in the military service, and ask him how long it takes to "cook" a machine gun barrel under very hard use. most machine guns have a cyclic rate of 4 to 500, or perhaps 6 to 700 rounds a minute, which is upwards of 10 rounds a second. (even at that rate, that means that for each second in which 10 rounds go down the barrel, that is only 10/1,000's second of exposure, and 999/1,000's second in which the barrel does not have the maximum exposure to the heat, cutting, erosion and friction of a bullet traversing the barrel.) and, when you consider that even in a machine gun, the gunner's asst. has to be feeding belts and magazines into the gun to keep it supplied with fodder and firing, the actual rate of fire deliverable from a machine gun is about 150 rounds or so a minute.
even so, machine gun barrels get chewed up in a hurry in "continuous" fire, which is why it is very desirable in a tactical and strategic sense for a machine gun crew to be able to change barrels very quickly, in the heat of battle: in the best of machine guns, it can be done very quickly, indeed. it's also why the smart machine gunner will have a couple asbestos gloves with him, in spite of what the e.p.a. may think of that, in case he inadvertently grabs a nearly red hot barrel in the wrong spot while changing it. a rather unforgettable experience, i should imagine.
now, i went to the range today to test my loads, and to see if i am on the right track with my load.
i fired 6 rounds. over a period of 20 minutes or so. in cold weather. even so, i checked the barrel between shots, to make sure the barrel was not heating. (it's a simple procedure, ... , you grasp the barrel with an un-gloved hand.) so, the total exposure of the barrel to all the un-pleasantries of the rifle propellant's temperature and cutting characteristics, was about 6 to 10 1/1000's of a second.
i've got a ways to go towards expending the 10 to 15 seconds of barrel life, under use.
john jay @ 12.23.2011
p.s. for a fascinating analysis of what happens to gunpowder after its ignition, during its burning and then its cooling upon the exit of the barrel, look to this very thorough analysis of the composition of gun powders and their residues at this forensics site, http://www.wavesignal.com/Forensics/GSR.html .
an acetylene flame, upon exposure to air burns at about 2400 degrees centigrade, and 3100 degrees centigrade upon admixture with additional pure oxygen. (that why acetylene torches have an oxygen bottle attached, as well.) http://www.engineeringtoolbox.com/flame-temperatures-gases-d_422.html .
let's see if i can find the temperature of the gases produced by the ignition of modern smokeless powder in the closed vessel of a gun's chamber and barrel, and, if i am lucky, what happens to the hot gases when they reach the open atmosphere. (hint: this latter occurrence, is what makes a gun go "bang." the gases burn like crazy, for a bit, expand incredibly producing a shock wave, e.g. "bang," and then the atmosphere comes rushing back into the comparative vacuum with another shock wave, prolonging the "bang." and, it all resonates. how do i know that? well, it has to, now, doesn't it. everything resonates. laughing.)
this is pretty interesting. but, i cannot find anyone who says exactly what the temperature of the powder gas is while burning in the confined areas of the rifle's chamber and barrel. aggravating, this. but, in the meantime, read this. http://www.z-hat.com/Efficiency%20of%20the%20300%20Hawk.htm
the answer: as to the question, how hot does smokeless powder get in a rifle barrel. well, it turns out that the answer is a bit more complicated than i thought. i found an abstract (actually, a first page in lieu of an abstract) at this site, and it appears that you can find out the answer, over the web, for what i expect is probably a small fee, or you can go to a very large and very good library and obtain the paper there. but, at any rate, here is the address of the website which will give you a leg up on your query, ... , actually, my query, eh? and, i will keep looking. but, tonight, it is time for the pbs. http://pubs.acs.org/doi/abs/10.1021/ie50257a006 and, for printed materials.
Actually, it's been judged that rifle barrels last about 5 to 5.5 seconds before accuracy is sufficiently degraded to warrant replacement. Computing that is a bit complicated because in the process of determining the total time each bullet is in the bore its acceleration must be figured in, and it accelerates the entire time it is traveling from chamber to muzzle. Just because the bullet exits the barrel at x feet per second doesn't mean its entire barrel time may be computed using that figure. If one did use that figure, however, and also assumed the upper time limit (5.5-6 seconds) one's estimate of barrel life wouldn't be off by much.
Posted by: Chuck | December 24, 2011 at 04:15 AM
Clearly the .300 Hawk is very energy efficient. Energy efficiency reduces climate change. Sure, Hawks are expensive and they won't work in guns we already have, but we cannot wait for the market to sort this out. The government must take action to save the planet.
I demand legislation to:
(1) ban all other energy wasting .300 & .308 cartridges
(2) provide federal subsidies to make .300 Hawks cheaper to buy
(3) offer tax credits for rechambering or purchasing new barrels
Now don't get too impatient. We'll need to give the lobbyists and politicians time to invest in some Chinese ammo plants to crank out the .300 Hawk using cheap toxic powder.
Posted by: sDee | December 24, 2011 at 08:48 AM
sDee:
a little smile creases the part beneath my nose.
laughing.
an able commentary on the state of the world in any number of ways. smiling, ruefully. very able.
personally, if i get to be dictator i will simply assert that all cartridges save the .280 british and the 7mm remington magnum, and the 6.8mm remington spc be banned.
to heck w/ patience.
render the lobbyists for heating oil, and screw the chinese.
merry christmas to you and yours, and a prosperous new year to you, sDee, and many happy returns.
thanks for the read, & thanks for the comment.
john jay
Posted by: john jay | December 24, 2011 at 09:54 AM
chuck:
with regard to average duration of the bullet in the barrel, i agree in general with what you say.
with this caveat.-- and, that is, that is "depends" a bit, "depending" upon the cartridge. "overbore" cartridges shooting a long for caliber bullet can use all the barrel they can get to squeeze out the last little bit of velocity. i wouldn't think, for instance, that in terms of velocity that a 28" barrel on a 7mm mag would be "wasted." on the other hand, a .308 winchester really doesn't need much more than an 18" barrel to get most of the velocity from any given bullet, ... , any gains from appreciably longer barrels are pretty marginal.
and, while what you observe about velocity in the barrel is in the main pretty true, but it doesn't take the bullet very long at all to gain most of the speed its going to get, that being a very big reason that pressure in the barrel and the chamber fall off pretty quickly as the bullet accelerates down the barrel.
but, in the main, i should think your observations pretty much hand in hand in mine, and i will admit that i didn't press the issue of overall time as much as i might have, because i didn't want to run into "the great wall of incredulity." i was full expecting that if i got any comment at all, i would get, "but uncle fred's been shooting the same rifle for 35 years now, and it's o.k."
i agree with you, very much in principle. measured in terms of "real time" exposure to all that goes on in a barrel in the very brief duration of a rifle shot, it does take very much time at all to destroy the utility of a barrel in terms of peak function. 5 to 10 seconds will do it.
it has been remarked in many places that loading manual technicians had very had times researching loads on the .264 winchester magnum, because they tended to wear out barrels in as few as 500 rounds of ammo.
500/1,500's of a second, or even 500/1,000's of a second, cumulatively speaking, is not a very long time.
at all.
john jay
p.s. thanks for the read, and thanks for the comment. it is much appreciated.
and, merry christmas and happy new year, to you and yours.
Posted by: john jay | December 24, 2011 at 10:07 AM