accuracy/fouling question for S&W 617 owners

My (problematic, soon to return to S&W) 617 seemed to gradually lose target accuracy over the course of shooting probably 50-60 rounds of CCI standard velocity lead nose. I was attempting to dial in a red dot, so I was using a laser inserted in the barrel, and it appeared as I went that the barrel must have been getting fouled, because it was harder and harder to insert the laser pointer the more rounds I fired. And my shots got further and further off.

Now, I've not put it on the bench for a cleaning yet, but I started off with a real clean gun. I've not thought that CCI standard was particularly dirty ammo. But has it been folks' experience here that less than 100 rounds would foul the barrel this much? I'm new to the revolver game, so is this simply typical, and I should have a bore snake at the range to run through more often?