How did you determine that this was the caliber? Is the gun so marked some where? What kind of gun is this, who made it, when? Pg. 67 European sporting cartridges lists (EXP46) 11.15 x65R LK Express
"This was the most popular calibre of the series listed to WWII by Geco & relatively common today. Listed by most German ammunition companies. This appears to be the same calibre as the 11.2x65R Collath (GPS16)." It looks like you might be in luck in finding some!

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