for the purposes of promoting an understanding of the principles of the invention , reference will now be made to the embodiments illustrated in the drawings and described in the following written specification . it is understood that no limitation to the scope of the invention is thereby intended . it is further understood that the present invention includes any alterations and modifications to the illustrated embodiments and includes further applications of the principles of the invention as would normally occur to one skilled in the art to which this invention pertains . fig1 depicts a fastener impacting device 100 including a housing 102 and a fastener cartridge 104 . the housing 102 defines a handle portion 106 , an air receptacle portion 108 and a drive section 110 . the fastener cartridge 104 in this embodiment is spring biased to force fasteners , such as nails or staples , serially one after the other , into a loaded position adjacent the drive section 110 . a trigger 112 extends outwardly from the housing 102 and controls the supply of compressed air which is provided from a source of compressed air through an air supply hose 114 . referring now to fig2 , which is a simplified depiction of the internal components of the drive section 110 , a piston 120 is located within a cylinder 122 . a drive blade 124 is located at one end of the piston 120 and aligned with a drive channel 126 into which a fastener to be driven is forced by the fastener cartridge 104 . a bumper 128 is positioned at the end portion 130 of the cylinder 122 which opens to the drive channel 126 . the bumper 128 , shown in additional detail in fig3 - 5 , includes a flange 140 , a number of vents 142 , and an extension area 144 . a drive bore 146 extends completely through the bumper 128 . an inner lip 150 is located between an outer passage 152 and a lower passage 154 in each of the vents 142 . each lower passage 154 communicates with an upwardly extending flute 156 within the drive bore 146 . a portion of the upwardly extending flutes 156 extend in the drive bore 146 along a cylindrical throat 158 which exhibits a uniform diameter . above the throat 158 , an upper conically shaped portion 160 of the drive bore 146 extends outwardly and upwardly to an upper surface 162 . below the throat 158 , a lower conically shaped portion 164 of the drive bore 146 extends outwardly and downwardly to a lower surface 166 . an outer surface 170 of the extension area 144 extends between the upper surface 162 and the flange 140 . two grooves 172 and 174 extend radially about the outer surface 170 . the groove 172 includes opposing walls 176 and 178 which are set at a right angle ( 90 °) to each other . the groove 174 is similarly shaped . the bumper 128 in this embodiment is constructed using a microcellular polyurethane elastomer ( mpe ). mpes form a material with numerous randomly oriented air chambers . some of the air chambers are closed and some are linked . additionally , the linked air chambers have varying degrees of communication between the chambers and the orientation of the linked chambers varies . accordingly , when the mpe structure is compressed , air in the chambers is compressed . as the air is compressed , some of the air remains within various chambers , some of the air migrates between other chambers and some of the air is expelled from the structure . one such mpe is mh 24 - 65 , commercially available from elastogran gmbh under the trade name cellasto ®. the manner in which the bumper 128 is deformed when subjected to an impact is a function of the particular geometry of the bumper 128 , the cylinder 122 , and the piston 120 . with respect to the cylinder 122 , the end portion 130 has a diameter that is closely matched with the diameter of the flange 140 . accordingly , a lip 180 , shown in fig2 , which extends about the end portion 130 retains the bumper 128 within the end portion 130 of the cylinder 122 . the diameter of the extension area 144 , however , has a diameter that is less than the diameter of the cylinder 122 resulting in a gap 182 between the outer surface 170 of the bumper 128 and the cylinder 122 . the relative diameters of the extension area 144 and the cylinder 122 , and thus the size of the gap 182 , is selected to reduce or eliminate contact between the extension area 144 and the cylinder 122 as the bumper 128 is compressed . contact between the extension area 144 and the cylinder 122 can decrease the working life of the bumper 128 . additionally , the radially formed grooves 172 and 174 , the shape of the drive bore 146 , and the vents 142 guide the manner in which the bumper 128 deforms as described below . with initial reference to fig2 - 5 , operation of the fastener impacting device 100 begins with the fastener impacting device in the configuration of fig2 . in fig2 , the piston 120 is at the rearward portion of the cylinder 122 and a fastener ( not shown ) is positioned in the drive channel 126 . in this embodiment , the drive blade 124 is configured to extend into the drive bore 146 . in other embodiments , the drive blade 124 may be spaced apart , but aligned with , the drive bore 146 . additionally , the drive bore 146 and the drive blade 124 are aligned with the drive channel 126 . when the fastener impacting device 100 is positioned against a work piece , the operator manipulates the trigger 112 resulting in venting of compressed air into the cylinder 122 at a location behind the piston 120 ( to the right of the piston 120 as viewed in fig2 ). the compressed air forces the piston 120 to move in the direction of the arrow 184 of fig2 toward the end portion 130 of the cylinder 122 . when the piston 120 reaches the position shown in fig6 , the fastener ( not shown ) has been driven by the drive blade 124 and the kinetic energy remaining in the piston 120 may be transferred to the bumper 128 . in fig6 , the piston 120 is in contact with the upper surface 162 of the bumper 128 . the throat 158 has a diameter that is larger than the base 186 of the drive blade 124 . thus , the bumper 128 does not contact the drive blade base 186 . continued travel of the piston 120 in the direction of the end portion 130 of the cylinder 122 begins compression of the bumper 128 . air forced out of the bumper 128 is vented through vent holes 188 . the vented air removes some of the heat that is generated by the deformation of the bumper 128 . the amount of mpe to be compressed in the bumper 128 has been selected such that when the piston 120 reaches the position shown in fig7 , substantially all of the kinetic energy initially in the piston 120 has been transferred to either the driven fastener or the bumper 128 . additionally , as shown in fig7 , the size of the throat 158 along with the taper of the upper portion 160 and lower portion 164 of the drive bore 146 has guided deformation of the bumper 128 such that the bumper 128 is not in contact with , or is only slightly in contact with , the drive blade 124 and / or the drive blade base 186 . likewise , the gap 182 resulting from the difference in diameter of the extension area 144 and the cylinder 122 , along with the sizing and location of the grooves 172 and 174 , have guided deformation of the bumper 128 such that the extension area 144 is not in contact with , or is only slightly in contact with , the cylinder 122 . once the kinetic energy from the piston 120 has been transferred to the bumper 128 , the piston 120 is returned to the position shown in fig2 . movement of the piston 120 away from the bumper 128 allows the resilient characteristic of the bumper 128 to reform into the shape shown in fig2 . as the bumper 128 reforms , air is provided through the vents 142 to the upwardly extending flutes and the drive bore 146 . air also flows through the outer passages 152 toward the cylinder 122 . this air , in addition to refilling air chambers within the bumper 128 , removes additional heat from the bumper 128 . the remaining air then passes into the area of the cylinder 122 between the bumper 128 and the piston 120 . one embodiment of a bumper 128 made from mh 24 - 65 mpe which provides desired kinetic energy transfer and deformation has an overall height of 44 millimeters and includes a flange 140 with a diameter of about 66 millimeters and an extension area 144 with a diameter of 52 . 6 millimeters . the outer passages 152 and the lower passages 154 have diameters of 4 millimeters and the upwardly extending flutes 156 are 4 millimeters wide , about 6 . 2 millimeters deep , and extend upwardly along the drive bore 140 to a height of 25 millimeters above the lower surface 166 . the throat 158 has a diameter of 20 . 1 millimeters and the upper conically shaped portion 160 has a height of 18 . 1 millimeters and is formed with a cone angle of 20 ° about a longitudinal axis 190 ( see fig5 ). the lower conically shaped portion 164 has a height of 13 . 1 millimeters and is formed with a cone angle of 20 ° about the longitudinal axis 190 . the grooves 172 and 174 in this embodiment are about 2 millimeters deep and , at their widest point , are 6 . 9 millimeters wide . the outer surface 170 extends between the grooves 172 and 174 for a distance of 3 . 2 millimeters . these dimensions may be modified for different applications or design requirements . while the invention has been illustrated and described in detail in the drawings and foregoing description , the same should be considered as illustrative and not restrictive in character . it is understood that only the preferred embodiments have been presented and that all changes , modifications and further applications that come within the spirit of the invention are desired to be protected .