Explanation of Markings on A hollis and sons shotgun

[captrakshitsharma]

Hi Friends..
Posted this query on my previous post of firing shaktiman slugs and balls in the above mentioned shotgun. Some friends advised me to chkeck chamber length 65 or 70 mm and the chokes on barrel. i was however unable to make out anything from what is written on the gun . So i forward the numbers and words on the bottom of barrel please solve the mystery and decrypt it so i become more aware of my gun use it properly and also preserve it for future shooting. Once again i thank you all.
Here is what the gun says... 13/1 NP BV Nitro Proof 1/4 S&B 4 1/2 DRS .. in a quadrangle ( triangle on top of inverted triangle) it says 12C and between the Barrels on the underside on the joint plate 621 is engraved..

regards to all

[snIPer]

Hi captrakshitsharma,
Can you please post pics of the Gun and also some with the markings.
/s/