Your cartridge release button (cartridge stop - #29 in image below) appears to be missing.
View attachment 600173
View attachment 600174
The stock has also been altered significantly.
Logical options would be to restore to original specifications (stock may be difficult to obtain), further 'sporterize' it to your own preferences, or enjoy shooting 'as is' (are there any sights on it?).
Regardless, get a box of proper fitting cartridges, take her out and shoot her, You may find yourself to be a lifelong MS fan thereafter.