Yes.
175-350 USD
It means you have a Mossberg Model 500a shotgun with the serial number L109563.
50-250 or so
You can determine the age of a Mossberg 500A shotgun by checking the serial number. Mossberg's serial numbers typically include a letter prefix followed by a series of numbers, with the letter indicating the production year. You can contact Mossberg directly or visit their website for more detailed information on decoding the serial number to determine the firearm's age.
Try e-gunparts.com, gun show, gun shops, want ads.
No
All.
If you have a 500, and it is a 12 gauge, it is a 500A. The "A" designates it as a 12ga. A 500B is a 16ga, a C is a 20ga, and an E is a .410.
It can be, if you are using a slug
You will have to call the company to find out.
Yes, it is. The 600AT was simply sold under the New Haven name instead of the Mossberg brand. It's a Mossberg 500A (12 gauge) intended for targets and hunting (long barrel and great wood). All Mossberg 500 parts fit it.