The company was originally Union Armera. Grulla with an engraving of a crane was their trademark. Various boxlock and sidelock models, I seem to remember the M205, M210 and M215 as ascending grades of boxlocks. Union Armera was a comparable competitor to AYA, Victor Sarasqueta until the early 1980’s when 22? of these Spanish gunmaking companies joined a government sponsored co-op to make and market guns. Within a few years the effort fell apart ( we’re the government, we’re here to help you) and most of the participating makers went bankrupt. AYA and a few others survived and carried on. Union Armera came out of bankruptcy and restructured under the company name of Grulla Armas with a goal of making only high grade guns and continue in business today. Do not make the mistake of confusing older Union Armera branded guns with the Grulla trademark with newer best quality Grulla branded sidelock guns. The earlier guns are very nice but quality and market value are much different than the newer guns. A simple search of your gun by brand name and model will yield important results.
A few more dim memories creeping out of the cobwebby recesses of my mind…….I believe the Union Armera models in the 200 series
(201, 203, 205, 206,)etc.,were boxlocks of ascending grade and price with the 200 as the base model. The more expensive line of sidelocks were numbered starting at 210 and ascending at least to the 215 or higher. 20 gauges in any of these are quite scarce and command up to a 25% premium in price, more in some markets.