I doubt you'll get much of an effective pattern at 60-70 yards, but you'll have to shoot a few to find out. Make sure you have some LARGE pieces of paper or cardboard (like 4' x 4') so you can see where the pellets hit. Until you get another gun, you're stuck with the IC choke, so find the range where most of your pellets stay within say a 10"-12" circle and call that your effective range if you are hunting deer. But better yet, if you get another gun, skip the buckshot and go to a slug gun.

If you can use slugs where you are, try some Federal Tru-ball style slugs. I hear they are good in smoothbores. You'll undoubtedly get more effective range than with buckshot. Aiming with a front bead sight only is tricky, so be consistent with your sight picture.