When a rifle w/ a longer barrel is fired,the force of expanding gases acts on the bullet for a longer distance

Question

what effect does this have on the velocity of the emerging bullet? Why do long range cannons have such long barrels?

Answer 1

W = FL; where F is the force (P/a) on a bullet of cross sectional area a acted on by a pressure P over the length of a barrel L. W is the work done on the bullet and that gives us W = 1/2 mU^2 = KE; where work converts to kinetic energy with velocity U at the muzzle.

If the force were the same for l < L; where l is a shorter barrel, then W/w = 1/2 mU^2/1/2 mu^2 and W = w(U/u)^2; so that FL = Fl(U/u)^2 and L = l(U/u)^2. Thus, U = u sqrt(L/l) and since L/l > 1 (L is longer) U > u. Thus, longer barrels (L) will have greater muzzle velocities (and KE) than comparable shorter barrels. For example, from U = u sqrt(L/l), if the barrel L = 2l, then U = u sqrt(2) = 1.4u a bit over 40% faster than a comparable short barrel.

One bit of caution here. The forces f and F are not constant over the lengths of the barrels. This results as the initial pressures (at the cartridge) diminish with the expansion of the propelling gases as each bullet rushes along the barrel lengths to the muzzle. But the change in pressures and forces is small; so it is fair to consider the forces and pressures as constant while each bullet head for the muzzle.

Bottom line, the work done on a bullet is greater over the longer barrel. Therefore, its kinetic energy and, therefore, muzzle velocity will be greater than a comparable shorter barrel.

Answer 2

The explosive gas stops pushing on the bullet after it exits the barrel, and the pressure is released. The rest of energy in the gas is wasted, so longer is better as far as bullet speed is concerned. The only reasons for restricting barrel length are practical ones like weight, portability, and manageability

Answer 3

The bullet is acted upon for a longer period of time in the longer barrel giving it more forward motion that increased by the extra time. Long range cannons have long barrels expressly for this reason.

Answer 4

yet another considerable ingredient has to do with the ratio of length to thickness. A shorter fatter barrel may well be greater precise than an prolonged skinnier barrel by using fact the long skinny barrel is far less inflexible and greater services to vibration and circulation than a stout, inflexible, fat, short barrel. You do unfastened some speed with a shorter barrel, yet there comes a ingredient the place too a lot barrel length will additionally unfastened speed do to friction that overcomes the accelerating tension. greater speed will develop rotational spin speed. a million in 12" at 1200fps has a slower rotation velocity than a million in 12" at 4000fps. How this impacts accuracy? usually twist is desperate for a given bullet weight and extremely an outstanding determination velocities. The velocities do not substitute usually adequate with production unit ammo to warrant adjustments in twist with adjustments in speed by using a shortened barrel. In all with 4" shaved off, and if a stable interest is performed you may even see a average progression in accuracy exceptionally if there is any harm performed to the crown of your muzzle. a stable real crown continuously helps the bullet to depart the barrel in a uniform way. there could be an optimal length in spite of the shown fact that it may be puzzling to discover it without gadget like the B.O.S.S. (Ballistic Optimizing capturing gadget) that shall we you incrementally alter the dimensions of the barrel to seek for the ideal length. i could pass the muzzle ruin. they have an inclination to make rifles louder and a .308 would not have a lot flinch which you extremely want one. For the money, except you do have a broken crown or muzzle, i could spend the money on a set off interest if not already performed. That by myself will help you control the set off without stressful the attractions. that could be a lot greater user-friendly wth a stable set off. learn how to handload. by using custom transforming into the around you hearth you will ring greater accuracy out of a rifle than you are able to think of! the main important reason in the back of you to decrease that barrel. the greater desirable 4" gets in the way and the gun would be handier...