Just got a brand new shipment of these in the back door right now less than a minute ago!
Back in stock:
And for the pinnacle of ultralight full-cap magazines to go with a light backpack takedown rifle, the obvious answer is:
TI25 Composite Magazines
The composite TI25s weigh less than the aluminum ones and are also fully adjustable and serviceable, so they're ideal for field use. A couple will easily fit in the front lower pocket of the Ruger backpack, along with over 500 rounds of boxed ammo in the front upper pocket of the Ruger backpack. That's how my personal 10/22 Takedown/TI25 combo is set up. Great combo!