I agree with Kirk on GunBroker completed sales.

You may also want to check out Rock Island Auctions dot com and look at the completed auctions.

Midwest Gun Works in StL has a long history with Browning so they may be able to assist.

You will have to do some manual research, but copy/paste this address into you browser:

https://truegunvalue.com/shotgun/BROWNING-A5-16-GAUGE/price-historical-value

I had a 1915 Model 12 in 16 gauge that only brought $400.

Good luck