In 100% condition, this gun is booked at $300.
Answer
I own a model 500, serial # 193258, that I bought new about 1965,BM,(before married). It has been lightly used, mostly trap shooting at that time. I think that the value you have of $300 is very low for a mint condition side by side, if you can even find one. If the mint is available at that price, let me know.