[subego]

Originally Posted by ghporter 

That’s true. With a longer barrel you have more “barrel time,” which equates to more time to burn more propellant and thus theoretically increase velocity.

However, that may not be necessarily useful or desirable. The recoil energy of any firearm - the “push back” against the shooter - is a function of the mass and velocity of the projectile. Even a fairly small mass, pushed at high enough velocity, can cause “undesirable” recoil. The mass of the weapon can mitigate this, but only to a point.

As to railgun-type weapons, I don’t know if there’s a point at which the accelerator can no longer add energy to the projectile. I need to research that.

For railguns I’m assuming whatever we can impart with barrel length X, we can impart more with 2X. Emphasis on assumption. I haven’t gone much beyond that due to the theoretical nature. Off-the-cuff, there’s going to be a limit in atmosphere because the bullet will melt. Probably not one in space.

As for recoil, I haven’t bothered with any calculations because this system is built into a powered exoskeleton. Also, if it uses chemical propellant, the charge would be very tiny because of the volume issue I noted above.

To give a very rough idea of some of the energies involved from the super-simplified ballistics model I’m using, a 2mm bullet with 100J would penetrate just as well as a 9mm with 400J.

Of course, the 9mm will cause a lot more damage on the way through. Relevant if the target is a person.


Edit:

[subego]

Originally Posted by Laminar 

Pedant stick incoming...volume of a cylinder is based on the square of the radius, so you would actually need a barrel that's 10^2 as long.

That’s… not pedantry.

I’m an idiot. Thank you for the correction!

[subego]

Originally Posted by reader50 

Soldier: Wow. I've often dreamed of a gun with no trade-offs ... *reville sounds*
Soldier (awake): Damn. Not again.

No offense was intended. I assumed you understood gun design involved compromises.

What I was getting at was this specific type of trade-off (spin-stability versus velocity) is the kind gun design is filled with.

[subego]

Originally Posted by subego 

Edit:

Notes:

It addresses blowing your hand off at the expense of not being able to use a steering wheel.

The book apparently says it’s 2mm. That’s bigger than 2mm.

[reader50]

My dialog sample was a joke. Not a disagreement. I suppose it counts as an agreement.

During S3, at one point the camera gets close enough to read an ammo case for a goliath suit. The case is labeled "6.25mm Incendiary Caseless Ammunition". That size looks compatible with your picture above. It's a hair under 1/4 inch.

[subego]

Originally Posted by reader50 

6.25mm Incendiary Caseless Ammunition