I spent years on Blue flying to the US 4 times a year and never got anywhere near Silver - until I discovered a secret.

If you look at the booking page on BA.com you will see
Ticket type: Lowest price or Flexible condition

but if you login to your account you will see
Ticket type:
Lowest price (earning reduced Tier Points)
Lowest price (earning full Tier Points)
Flexible conditions (earning full Tier Points)

The middle one is the passport to Silver. You pay a little more for the flights but you get the full TPs. On reduced TPs it's going to be virtually impossible - in fact it used to be even more impossible but BA have recently increased the minimum TPs rewarded for the lowest price tickets.

If you can stretch to WTP then you can get to Silver by 4 returns to the US each year.