Looks to me to be an off catalog shotgun; something made to a modest price point for some retailer. The number of visible pins in the lock isn't really very informative, other than to suggest the era in which it was made and where in the range of price points the gun may fall.

If you want to compare your gun to the line of Arrieta side lock on offer, go here:

https://www.arrietashotguns.com/en/portfolio_page/magister-2/