minor adjusts

src/Main.sol

@@ -202,9 +202,10 @@ contract Main is Owned {
     /// @dev The likelihood of killing a boomer decreases as time goes on - i.e. more duds
     /// @param _amount Amount of bombs to send to kill Unaboomers
     function sendBombs(uint256 _amount) external missionNotCompleted {
-        require(_amount <= bombBalance(msg.sender), "not enough bombs");
-        require(_amount <= unaboomer.totalSupply(), "not enough supply");
         uint256 supply = unaboomer.totalSupply();
+        require(_amount <= bombBalance(msg.sender), "not enough bombs");
+        require(_amount <= supply, "not enough supply");
+        require(_amount <= supply - unaboomersKilled(), "not enough active boomers");
         for (uint256 i; i < _amount; i++) {
             uint256 randomBoomer = uint256(keccak256(abi.encodePacked(i, _amount, block.timestamp, msg.sender))) % supply;
             bool dud = unaboomer.tokenDead(randomBoomer);

test/Unaboomer.t.sol

@@ -67,7 +67,7 @@ contract UnaboomerTest is Test {
         hoax(address(2));
         main.sendBombs(10);
         hoax(address(1));
-        main.sendBombs(25);
+        main.sendBombs(20);
         uint256 ptr = main.leaderboardPointer();
         address leader = main.leaderboard(ptr);
         uint256 killcount = main.killCount(leader);