Art,
Yes, there's erosion past the leade (throat?) or whatever you call the angled rifling from freebore diameter down to bore diameter. It's not as much as on the angled rifling. And there's usually more in the bottom half of the barrel 'cause that's where the powder and primer residue settles. It acts as a lapping compound as following bullets press then rub it against the barrel steel. All of which means bullets won't shoot as accurate after some amount of erosion. Sometimes it can be seen as a dark area at the bottom of the chamber at the origin of the rifling compared to the area at the top which is brighter.
Some folks cut the chamber off at its mouth on a barrel that's about 3/4ths worn out then reshank and rechamber it. The reamer takes out nearly all of the erosion. That barrel will now last about 80% as long as it did originally.
And some will repeat this all over again. Starting out with a 30" barrel is a boon to such adventures.