Inserting Data Into SQL Server

declare @counter int

select @counter=300000
while @counter > 0
begin
insert into Revenue (Instr_type, Tel_no, Phone_Id, Rpt_date, Pay_mode)
values("PP0073", @counter, "080464", "19990901", 1)
select @counter=@counter-1
end

HI there,
I run the above statement in Query Analyzer and the expected result should be 300,000 records inserted into Revenue table. But unfortunately the actual records inserted were less than 300,000. I also realise that it insert different amount of record each time I run it. Can anyone please tell me why?

Thanks,
Will