en.wikipedia.org
I should let you know there's full-auto versions of the M1 Garand.
Also, I'd morally want you to win cause who the heck would morally, ethically or legally back a known serial killer...?
In any case, you're dealing with an experienced (even if impulsive) serial killer, you might as well start preparing physically and mentally to ideally kill him in return or at least incapacitate him well enough that either you can escape and find ways to bring him to justice by alerting help or trap him in a place where he is incapable of escaping thus basically giving him an ad hoc life imprisonment in solitary confinement and potential eventual death since you're definitely not gonna provide him basic needs.
You're gonna need to take cover and concealment via good environmental usage (trees, rocks, fountains, kids' playground slides and other facilities and amenities, etc etc), set off the fireworks via the lighter either as a weapon or a distraction but do it in such a way that you can keep your location hidden, and keep a goddamn watch for any sensory stimuli that might clue you in to his location (visual, auditory, olfactory, tactile, etc), so you can get the first shot with your M1 Garand, which should be more powerful than his pistol.
(You could also build traps perhaps that involve sharpening the metal pipe to either use as a spear or a punji booby trap stick as well as firecracker firework ad hoc IEDs or mines or whatnot, but that may take too long and give away your location as well.)
If you fail in any of these, ESPECIALLY watching out for stimuli like visual and auditory cues like the chainsaw or pistol or just failing to watch/be aware of your surroundings 360 degrees 24/7, you would risk being shot, chainsawed or stabbed from behind.
