Barrel cleaning observation

The last time at the range I brought up 6 milsurp rifles and a mouse gun. We shot them extensively. When I got home I did my normal cleaning, which is gross over kill by any standards. I can't stand dirty barrels, not even a smudge will pass on a white patch when completed. Yesterday I did an inspection of a few guns in the locker room and on one of the guns I had out I saw what looked like very small hairs stubs in the barrel. I figured it may be dust but wanted to be sure so I soaked it with Hoppes BR cleaner for about a half hour scrubbed it with a new bronze brush and out came some crud, Hum. I took down the other guns from that day and on four of the six I found the same thing. They all got the same treatment and up came the same results. I cleaned the junk out of them and got them shining.then oiled them with a high end silicon lube. I then spent the next few hours checking the rest of the collection and all is well, it was only the guns I shot that day, two Lee Enfields two Finnish pot belly 91/30's the mouse gun was fine (Stainless) as were the Mausers. The only link here was I used the same brand of ammo on the problem guns, Ingram. Has anybody else had this experience with your shooters???-SDH :sos: