While I believe Der Ami is correct if you're going to want to shoot this gun spend the small amount to get a cast of the chamber or do it yourself as Dave described. Safety is always of primary concern to me and I'd rather be safe than sorry.
BTW: If you go the do it yourself route you'll need a dial micrometer preferably calibrated in millimeters to do the measuring.
Let us know the results
Jim

The 2nd Amendment IS an unalienable right.