I will assume its an ndoor range with a hard floor,probably concrete.
Fire is a 3 legged stool.It requires heat,oxygen,and fuel.
Not much chance of eliminating oxygen.
I'll grant your 454 loads are likely the source of ignition....the initial "heat"
I'll talk about reducing that at the end of this post.
Its not your 454 thats building up unburned powder on the floor. Thats "everyshooter"
I'm not sure,but I would guess the NRA or OSHA or the military or some police agency or someone has a recommended procedure for maintaining indoor firing lanes
I'm saying its probably not necessary to re-invent the wheel. And I'm saying there is probably an existing standard to meet.
That should keep the range fires in check. Its not just you that is the problem.If the range burns down,lack of maintnance could be an insurance claim problem.
A Dustex,the long dustmops like are used to sweep gym floors may work,but a powder filled Dustex is a hazard itself.
A vacuum might be effective,but a vacuum filter bag or cannister full of aerated powder dust flowing through,on,or about arcing motor brushes seems problematic to me.
Matbe a wet vac with a couple gallons of water in it? I don't know.
I can't tell you that would be safe.
Do some research. If you find a prescribed method,approach your range with the atitude of being part of the solution.
I would suggest that needs to be a nightly responsibility for whoever shuts down and closes up.
Now,what can you do to mitigate being the ignitor?
Are you using a strong roll crimp? Pretty critical.The cylinder throat offers no resistance like a rifle throat does. Then there is the cylinder gap,which allows pressure to escape.Then thereis the forcing cone in the barrel.
Your primer can blow the bullet that far. Slow burning magnum type powders have a lot of deterrent coating.They are harder and slower to light.
And some powders don't burn up worth a darn if you don't get them up to required pressure.
Example,you don't want to try to load reduced or moderate pressure loads with H-110 or 296.
I've seen mild 4227 loads leave unburned powder.
In closing:
Use load book recommended powders and charges...Work safely up from the min start load,but try not to stay there.Its best to be more midrange,usually.
If your cases get sooty,thats a clue . You aren't getting the pressure up to obturate the case and the burn is dirty.
Use a magnum primer when specified.
And use a strong,heavy roll crimp into a crimp groove.
With a heavily loaded 454 and 325 gr bullets,its possible recoil is pulling your bullets ,and you are losing your crimp. Then your loads would have poor ignition.
Thats all I have. Good luck,stay safe.
And actually having a fire extinguisher on hand might beat flinging water water jugs around.