Out of curiosity, why did you convert it? You can get resized .308 or full 7.92mm Mauser blanks from various sources used by the reenactment community that will give you a far bigger bang. Swanson Blanks is one of the ones I've used in the past. He does a lot of stuff for Hollywood too.
If you're lucky, you might be able to find some GL blanks (for grenade launching) - they're even louder, but whatever you do, STAY AWAY from vintage Israeli 7.92mm blanks. The Israelis got a boat-load of Mausers when they first set up their country back in the 50's - excess stores from post-WWII Germany (I chuckle at the irony there) plus training blanks. The crimps on that stuff is so old, you can actually blow pieces of crimped brass out the muzzle and is very dangerous to use.
And before you ask how I know all this stuff, I was a WWII Austrian reenactor since 1994 (hence my forum alias) and I am intimately familiar with the K98K Mauser Carbine. Yours looks in nice shape, BTW. Based on the maker's mark, it looks like one of the slightly newer Yugoslavian M48A Mausers (post-war).