Don't often frequent this forum, so don't know if this question has been asked before or not.

I got thinking about my old 8mm Rem. Mag. and a friend's .17 Rem. Both high velocity. The advent of smokeless powder put velocity into a whole different category, but has that envelope been stretched as far as it can go?

Is someone going to try a .17 BMG? With what little I know, it'd take a slow burning powder and looong barrel length to squeeze out the max velocity on something like that, if you could get it all out the throat of the case without it blowing up in your face first.

My buddy was able to scorch bullets out of his .17 Rem at high enough velocity to cause them to disintegrate. Not from the speed, but from the twist rate. Presumably, as velocity increases, you'd have to reduce twist in order to counter centrifugal forces that will take the bullet apart. Can we achieve velocities that will take us down to 1 in 4 or 1 in 2 twist? What would those velocities be? 10,000 fps?

Not an issue in the .17 Rem, but what about recoil. Will these super-hyper-velocity rounds even be able to be shot? (I remember my 8mm Rem. Mag. as having a kick akin to an Army mule! Worst kicking rifle I've ever shot!)

What do you think?

Fischer,
In theory, the velocity is limited only to the speed of the explosion produced by the smokeless powder. However, this velocity is well above what you are observing in your 17 Remington.
The problem with theory is it doesn’t jive well with practicality. If you were to neck .50 BMG down to .17 you would have a single shot rifle. When I say single shot I mean your barrel would be ruined after 1 shot due to throat erosion. (If it didn’t detonate upon ignition)

There have been experiments performed to test these types of questions. I have seen folks on this forum post data from a few of them, but suffice to say they have little practical application in the shooting/wildcatting community.

We have "Just about reached the velocity limit" for the last 55 years

I have heard that the "limit" for conventional firearms is around 5000 fps, which is supposed to be approaching the maximum speed that the gas in the chamber can expand.

There is a good article on this subject in "Cartridges of the World", it compares 22 caliber cases ranging in size from the rimfires to the eargesplittenloudeboomer (50 BMG necked down for 22 caliber bullets). As case volume increases, the velocity curve goes "flat" as you increse case volume.

Regards, Bill

Simply the laws of diminishing returns kicking in. It IS possible to fire bullets at 5000 fps with conventional cartridges (Saeed had something about using 30-gr Berger .224's to reach 5000 fps out of a .22-250). However, to have a usable cartridge, you need a bullet that has a better BC and SD than such a atypical bullet. Before we see the advent of a commercial 5000 fps rifle, we'll need to see new powders invented, bullets designed to hold up to that velocity, and probably most importantly a new material for rifle barrels. Even the best modern steel won't hold up to 5000 fps long before the barrel is toast. I've read blips about possibly using ceramics, ceramic-metal alloys (cermet) or such to create a more heat-resistant barrel, but I have no idea what happened to that research. That, I feel, is the current limiting factor. Peace.

The military reached a maximum for rifled tank guns which is why they have gone to finned, spin stabilized projectiles. I think the same it true for shoulder fired weapons. At speeds in excess of 3500fps, barrel erosion becomes a real issue. If I wanted to pursue pure speed, it would be a smoothbore with spin induced by deployable fins or discarding sabot. No need to rediscover the wheel. The only question is why? Ku-dude

9500 fps is basically the speed of the gasses expanding, right?

I've heard of 5500fps 50 bmg, with liquid fuel and bimetal (including moly) bullets...

man, liquid fuels just tip the iceberg at 5500 fps... 15000fps gass front!!

jeffe

The wave of the future?

How fast does a rail gun projectile go?

Short answer: currently about 4 km/s (13,123fps)

The speed of a rail gun slug is determined by several factors; the applied force, the amount of time that force is applied, and friction. Friction will be ignored in this discussion, as it's effects can only be determined through testing. If this concerns you, assume a friction force equal to 25% of driving force. The projectile, experiencing a net force as described in the above section, will accelerate in the direction of that force as in equation 3.

(3) a=F/m

a=Acceleration (Meters/second^2)

F=Force on projectile (Newtons)

m=Mass of projectile (Kilograms)

Unfortunately, as the projectile moves, the magnetic flux through the circuit is increasing and thus induces a back EMF (Electro Magnetic Field) manifested as a decrease in voltage across the rails. The theoretical terminal velocity of the projectile is thus the point where the induced EMF has the same magnitude as the power source voltage, completely canceling it out. Equation 4 shows the equation for the magnetic flux.

(4) H=BA

H=Magnetic Flux (Teslas x Meter^2)

B=Magnetic field strength (Teslas) (Assuming uniform field)

A=Area (Meter^2)

Equation 5 shows how the induced voltage V(i) is related to H and the velocity of the projectile.

(5) V(i)=dH/dt=BdA/dt=BLdx/dt

V(i)=Induced voltage

dH/dt=Time rate of change in magnetic flux

B=Magnetic field strength (Teslas)

dA/dt=Time rate of change in area

L=Width of rails (Meters)

dx/dt=Time rate of change in position (velocity of projectile)

Since the projectile will continue to accelerate until the induced voltage is equal to the applied, Equation 6 shows the terminal velocity v(max) of the projectile.

(6) v(max)=V/(BL)

v(max)=Terminal velocity of projectile (Meters/second)

V=Power source voltage (Volts)

B=Magnetic field strength (Teslas)

L=Width of rails (Meters)

These calculations give an idea of the theoretical maximum velocity of a rail gun projectile, but the actual muzzle velocity is dictated by the length of the rails. The length of the rails governs how long the projectile experiences the applied force and thus how long it gets to accelerate. Assuming a constant force and thus a constant acceleration, the muzzle velocity (assuming the projectile is initially at rest) can be found using Equation 7.

(7) v(muz)=(2DF/m)^.5=(2DILB/m)^.5=I(2DLu/m)^.5

v(muz)=Muzzle velocity (Meters/Second)

D=Length of rails (Meters)

F=Force applied (Newtons)

m=Mass of projectile (Kilograms)

I=Current through projectile (Amperes)

L=Width between rails (Meters)

B=Magnetic field strength (Teslas)

u=1.26x10^-6 (The magnetic permeability of free space, Henries/Meter)

These calculations ignore friction and air drag, which can be formidable at the speeds and forces applied to the rail gun slug. Top rail gun designs currently can launch a 2kg projectile (tungsten fin-guided projectile in aluminum sabot) with a muzzle velocity of close to 4km/s on roughly 6 meter rails. To reach this kind of velocity, the power source must provide roughly 6.5 million Amps.

extracted without permission from:

http://home.insightbb.com/~jmengel4/rail/rail-intro.html