If you have never seen one of these they are a great pistol caliber backpack/trunk rifles. They fold up to about 16.5". The different models can use a variety of common pistol magazines. I own a Glock 19 compatible rifle which uses Glock 19, 17 and their 33 round Glock 18 mags. Below are two links of where you can find them but with a little Google-Fu I'm sure there are better deals out there.
Rebate Link
Buds Guns
PSA
Rebate Link
Buds Guns
PSA