Drill bit assembly

1. A drill bit assembly, comprising:

a body portion intermediate a shank portion and a working portion, the shank portion being adapted for connection to a downhole tool string;

the working portion comprising at least one cutting element fixed with respect to the body portion;

the body portion comprising at least a portion of a reactive jackleg apparatus that is generally coaxial with the shank portion;

the reactive jackleg apparatus comprising a chamber at least partially disposed within the body portion and a shaft movably disposed within the chamber, the shaft comprising an enlarged portion and a hard metal distal end;

the chamber comprising an opening proximate the working portion, through which drilling mud from the bore and the distal end of the shaft exit the drill bit; and

the enlarged portion of the shaft is in fluid communication with a bore formed in the tool string;

wherein a position of the shaft is determined by at least a combination of a formation pressure and a fluid bore pressure generated by drilling mud;

wherein the enlarged portion of the shaft engages a spring.

2. The drill bit assembly of claim 1 , wherein the distal end comprises a wear resistant material.

3. The drill bit assembly of claim 1 , wherein the enlarged portion is movable to a closed position blocking said opening.

4. The drill bit assembly of claim 1 , wherein the spring generally coaxial with the reactive jackleg apparatus is positioned within the chamber and engages the shaft.

5. The drill bit assembly of claim 1 , wherein the distal end comprises at least one nozzle.

6. The drill bit assembly of claim 1 , wherein the shaft is retractable.

7. The drill bit assembly of claim 1 , wherein the distal end of the shaft protrudes beyond the working portion.

8. The drill bit assembly of claim 1 , wherein the body portion comprises at least one fluid port in communication with the chamber and the working portion.

9. The drill bit assembly of claim 1 , wherein a position of the shaft is also determined by a spring pressure.

10. A method for controlling weight loaded to a working portion of a drill bit assembly, comprising:

providing a fixed cutter drill bit assembly with a working portion and a reactive jackleg disposed within at least a portion of the assembly and being generally coaxial with shank portion of the drill bit assembly, the jackleg comprising a shaft with a hard metal distal end and an enlarged potion of the reactive jackleg is in fluid communication with a bore formed in the body portion of the drill bit assembly, the enlarged portion of the shaft engaging a spring;

providing the drill bit assembly in a borehole connected to a downhole tool string, and the enlarged portion of the reactive jackleg is in fluid communication with a bore formed in the tool string;

contacting a subterranean formation with the distal end of the shaft; and

pushing off of the formation with the shaft;

wherein a position of the shaft is determined by at least a combination of a formation pressure and a fluid bore pressure generated by drilling mud.

11. The method of claim 10 , wherein pushing off the formation occurs automatically in response to changes in formation pressure.

12. The method of claim 10 , wherein the method further comprises a step of contacting the formation by the working portion before the shaft contacts the formation.

13. The method of claim 10 , wherein contacting the subterranean formation also reduces bit whirl.

14. The method of claim 10 , wherein pushing off of the formation with the shaft is achieved by increasing pressure in the bore of the downhole tool string.

15. The method claim 14 , wherein the pressure in the bore is increased by forcing more drilling mud into the bore.

16. The method of claim 10 , wherein the jackleg is substantially coaxial with the drill bit assembly.