Hi please could some one offer me advise on putting a Martini Henry 577/450 on my Firearm certificate. I am looking to do a one for one variation with a an unused slot on my licence and am wondering on what to put

Calibre i assume i put .577/.450 ?

Type Rifle

Action Martini

Identification Number No Visible Number

If i do place a Martini on my licence and it changes from a Sec 58 antique to a Sec 1 firearm and find the rifle cant shoot worth alight can i change the rifle back to a Sec 58 ?