I read that det cord and other types of explosives have burn rates in excess of 30,000 fps.. We as reloaders are limited to the use of gunpowder and the laws of expanding gases, about 6000 fps.. Just curious, but where is technology headed in this area? A 40 grain Nosler from my Hornet, tooling along at about 25,000 fps sounds promising (moly coated of course).

Det cord is designed for the burn rate, not for the production of expanding gases to propel a bullet.
I think that the only way to realistically get to ultra high velocities is with a electro-magnetic rail gun. The last time I heard about one was a 30 ft unit propelling a 1 lb aluminum cased plastic projectile at either 16,000 or 22,000 fps, I can't remember which, it was in a popular mechanics magazine some years ago.
Sooner or later, someone will come up with a way to create a man-sized unit for a shoulder arm.
Just think about it, no recoil or muzzle blast, just need a battery and projectiles.

Oh there will be recoil, equal and opposite reactions and all. But there won't be a muzzle blast, so even a muzzle brake will have no effect.

I am also very interested in alternative propellants. I have been following the development of liquid propellants (LP) for use in guns. Several labs and universities have been doing research in this area. An internet search using the terms "Liquid Propellant Gun" should provide more info on this subject.

The US Army's Advanced Field Artillery System, AFAS, now called Crusader, is an autoloading self propelled 155 mm howitzer. For both logistic and performance reasons, the Army would like to use a liquid propellant for Crusader. Liquid propellent is easier to resupply (you pump it like diesel fuel), it packs more efficiently into tanks and drums, it fills the chamber with no void spaces giving greater energy density and it can be used incrementally with only as much propellent as needed for the range. Liquid propellent can also be injected in a precisely metered rate, to help make the pressure profile less spiky and more flat-topped. This gives more muzzle velocity for a specific pressure limit. The problem with just filling up the breech with liquid is that the pressure shoots up to a peak exponentially. To produce a nice long flat-topped pressure profile, the propellent must be metered into the chamber through the ballistic cycle. For Crusader a regenerative injector has been developed where chamber pressure pushes a piston, which forces more propellent into the chamber. Take a look at this web site for info on the Crusader system: http://www.fas.org/man/dod-101/sys/land/crusader.htm

I would like to see "Electronic Fuel Injection" on a rifle someday. Such a rifle may be under development now.