It’s close. A standard AR-15 upper with a 16inch barrel and A2 flash suppressor is about 26 inches. Perhaps if you fit it diagonally.
However, I wouldn’t use this bag for carrying a taken down AR for a few reasons.
First, there are already bags out there specifically designed for the purpose at about the same price point. They include straps on the interior to secure the parts of the rifle while in transit, a padded flap to separate the upper and lower, etc. Use the right tool, or in this case bag, for the job.
Second, and not an issue for some, is that the bag is too “tacticool” for me. I have friends who are what I call “couch commandos”. They love Call of Duty games and all of their gear MUST be tacticooled out and you can spot them from a mile away when they head to the range. I live in the city and when I’m toting my rifle around to the range, shop, or occasional hunt on my acreage I like to be discreet about it. It’s about a 40-50 yard walk from my apartment door to my truck past a playground with kids and parents usually enjoying it. I respect my neighbors enough to be discreet when I have to pass by them and their families with my shooting gear. Not everyone is comfortable with firearms (even here in Texas), especially around their families.
Google “discreet AR-15 case” and you should get plenty of solid options designed specifically for the purpose of carrying a taken down Ar-15. Mine looks like a slightly longer generic day backpack on the outside, but on the inside there are straps and pockets for my rifle, mags, cleaning kit, etc.
I’ve even seen a guy who modified an old and brand name tennis racket bag to carry his broken down rifle in. He added Velcro straps to the interior to secure his gear. When I see him at the range he looks like he got lost on his way to the country club. haha