After a recent range day at my department I saw a couple of guys using a nylon brush and a drill with the cleaning rod in it to clean their guns.  They used the drill at low to medium speed with the nylon brush and stated that they have never had any problems with their guns.  I have always cleaned my gun the old fashion way with a brass brush, patches, and rod; however I can’t but think that this could be bad using a drill.   This was done for both handguns and rifles.   Any thoughts?

I surely wouldn't do it with a firearm I cared about. The bore doesn't get that dirty and a few passes with a rod and a chamber guide is normally all that is needed.  Normally, anything powered used for cleaning is going to be a bad idea.

These clowns will soon have barrels that won't shoot, and they'll wonder why.

All this started with gunsmiths that used 0000 steel wool on a drill to polish and clean out badly fouled shotgun bores.
Trouble is, people heard of this and didn't stop to think that there's a big difference between a smooth shotgun bore and a rifled bore.

I've seen people doing this in rifled barrels with steel wool, Scotchbrite pads, bronze bore brushes and synthetic brushes.

A.  It really doesn't clean a rifled bore since it doesn't get the fouling in the corners of the rifling.
B.  It will absolutely ruin a rifled bore by rounding off the sharp edges of the rifling lands.
Don't bother trying to tell these guys any of this, they never listen.

I've never been able to understand why people who'll buy an expensive gun with a fine barrel will do this.  They'll spend days trying to find the "best" ammo, they'll discuss what's the best lubricant for hours on the internet, they'll agonize about what the best accessories are........ then they'll stick God knows what down the bore because some boob told them it was fast or CHEAP.

I figured they were on borrowed time.  I have just never seen this or heard of this and didn't know why someone would do this other than being lazy.

It's not a good idea to have abrasive nylon cutting across the lands and dulling the edges.  The brush won't get into the corners of the grooves spinning that direction anyway.

I was talking with my Uncle who was in the Veitnam war and he told me that they would use a drill and the brass chamber brush to clean the chambers on their M-16's, I guess the higher-ups were on their backs all the time to keep the guns clean because of the issues they were having with the M-16 back then. He did say that after they were done the chambers looked like a mirror. I'm not trying that on my AR though.

Cleaning the chamber area of an AR with a drill is fine...many people use this technique.  The issue is with using a drill in the bore of a rifled barrel.