mossberg 500 shotgun

Hey guys Ive been leaning towards a Remmy 870 for my first real shotgun (used my 20g for squirrel hunting but wanted a larger gun I could use to hunt deer locally since they frown on my rifles) but have just recently started leaning towards the Mossberg 500 more. That being said I am looking at...

I have to start off by talking first about a Winchester Model 1300 Defender 20GA. This was the only shotgun I had to use as a comparison to the Mossberg 500 Persuader. The 1300 Defender was and is a great shotgun. The finish on it was a parkerized finish to where the Mossberg 500 I bought is a...

For some reason I can't find an 18" barrel for this thing. I have been told at one place that they're on backorder, so maybe I'll just wait. Any ideas? I did find a slug barrel (24"). How bad will shot screw up the rifling?