The gun is designed to shoot longer than a shooter can use it.
Most clay shooters will shoot 1 box (25 shells) per round. A tournament in Skeet or trap is 4 boxes (100 rds). Five Stand and Sporting Clays shooters also will shoot similar round counts.
It is not uncommon for a shotunner to shoot 200 rds in one day [8 boxes]. I have personally shot 16 rounds of practice in one day with various shotguns, including the 870. Easiest way we broke in and smoothed up a new 870 was to just bring it out and let it be shot by any and everyone.
Four guys shooting sharing that one gun for 100 rds each - a fast 400 rds. In a day, it was not uncommon for a gun brought to repeat this again with another squad of 4, maybe even 3, 4 or 5 squads of 4.
Not uncommon to put 200 slugs at one time thru a gun. Take note of the round count a training class puts thru a gun per day, per class total.
Easiest way to smooth a 870 ( any shotgun) is to let everyone shoot it during a week that wants to. Too many guns over the years have survived a week of 2k, 3k even 5k rds in one week and went on to shoot over hundreds of thousands of rds.
Gun club rentals survive high round counts per day, week and years.
You will be fine.
I shot a particular 870 recently with over 300k rds thru it, made in the late 50's. Very smooth, and has been hot a time or three over its lifetime.