Actually this has been handled a few different ways, all depends on how you want it.
from another site was a nice idea if a bit flashy....
Mallorean Arms Gunblade The BladeGun is a semi-automatic heavy pistol with a large crescent shaped knife-blade attached in front of the trigger guard and grip. Also called the Samurai handgun, it incorporates styling found on the grips of katanas and Japanese kanji down the side of the slide and blade.
This pistol can accept only top and barrel mounts, the underbarrel mount taken up by the blade. The underbarrel weight of the blade gives the gun 1 point of recoil compensation.
Weapon: Blade Reach Con Weight Damage Cost Avail Index
Mallorean Gunblade 0 5 3.0 (STR+2)L 7,000n¥ 14/14 days 2
Weapon: Gun Con Mode Ammo Range Damage
Mallorean Gunblade 5 SA 20 Heavy Pistol 8M
A pair of these with adequate training in gun-fu and you got yourself some MA fun, mixing blades and bullets in any fight. The blade also acts as a partial guard for the hand so can be used for defense as well though I would personally weld on a bit of a bar at the bottom of the blade to meet the handle of the gun for pinky protection, but that is just me.