I recently came across and bought an older sxs made in Spain. The guage is 28. The chamber is 2 3/4 or 28mm. I located the word choke underneath the barrells but do not know how to interpret.

Under the word choke, numbers are listed like 13.6 or 1.36 (haven't looked at it in a couple days and may have the decimal in the wrong place).

I believe the gun to have been made prior to 1970.

Does anyone know of some good resources for me to check or have any info. you would pass along regarding 28 guage Spanish chokes designation. Thankyou.