I Worked in The Firearm Industry for 10 years Prior to Becoming An Officer. Your Three Best options are.
1. Pulling the Nipple and Trickling in Powder, Replace the nipple, cap & fire into something Soft to catch the Obstruction.
2. They Make A CO2 cartridge adapter ejector that Replace the Nippile on a Side Lock Or Breach plug on an Inline MZ.
3. Use A Barrel Vise And The " Correct " Wrench To Remove the Breach End of the Barrel. And While The Barrel is in The Vise, Drive Out the Obstruction.
On Storing Long Guns Including " MZ's " This Came from A Master Gunsmith, Who Apprentice Under A Grand Master Gunsmith. After Cleaning Heavily Oil The Firearm ( Not Dripping ) Just a Heavy Sheen, Let it Sit for 30 -60 minutes. Then give it a Quick Wipe down with a Clean dry 100% cotton cloth. Then Store " Muzzle Down " this prevents oil from Soaking into the Wood.
In Regards to The Side Lock Mz, THE Day Your Going Out To Shoot. Pull your nipple and Blow out your snail & breach plug with compressed air, and Don't be stingy. And Before Loading your First Charg, fire A Percussion cap through your nipple, to dry it out. I Think That You'll be Much Happier with the Results.