What is the most profitable 25-day investment I can make that guarantees that I at least get the principal back? Notes:
Many brokers accept credit card deposits w/ no fees, and the credit card company counts it as a purchase, so I have a 25-day grace period with no interest.
So, I can invest using my credit card, pull back the money within 25 days, and show a profit. I can then repeat the process monthly. I have 100K total spending limit, so the profit might be nontrivial.
I know Treasury notes/bills/strips (whichever ones expire in ~25 days) and money market funds are two options, but are there any more profitable ones?
I'm OK w/ the profit being variable (even zero), but need to preserve the principal to pay back my credit card.