Word spiral

Starting from 1, fill in the grid in a clockwise direction with four-letter words. The last letter of each word becomes the first letter of the next to reveal the seven letter key word in the shaded boxes. Keyword clue: English county

1. Counterfoil

2. Surety

3. Molten volcanic rock 4. Ammunition

5. Betting chances 6. Fastener

7. Flat circular item 8. Barrel

9. Make woollens 10. Pith helmet

11. Data

12. Wise birds

13. Music type 14. Heather

15. Food, informally 16. Explosive device