David, yes 10+1 is legal. The 10rd limit applies to the magazine only, so you can have 10 in the magazine and 1 in the chamber for a total of 11. Have a great day!

Hi David, yes Sir. All State restrictions specify the capacity of the Magazine. Chambering a round and then topping off the Magazine to 10rd yields 11rds total and is perfectly legal in all 10rd Magazine limited States. Cheers and stay safe!

David, yes sir, perfectly legal in Washington. 10+1 just means it's a 10 round magazine plus one in the chamber. So you're good to go as long as the magazine itself can only hold 10 rounds or less. Hope this helps

10+1 just means that while the magazine is capable of holding the state 10 round maximum, you may also chamber a round to give you a total of 11.
Hope that helped ya' out. Have a great day!