Blowback is the fire and smoke that "blows back" towards the shooter. Different rifles have different levels of it. The Encore for example has none. It's a completely sealed action. I've heard that some people get a little residue, but it's minor. My knight Extreme had a mild blow back that is pretty much all smoke and no fire. The blowback I'm refering to in the video was just a cap not a full load. A full hunting load would likely throw more than what the cap alone did. There are 3 or 4 clips showing this. One clip shows sparks flying right towards where the shooters face would be. That clip was using the included weather shroud.
Out of all the guns tested during both of his videos, only 2 were deemed discraces. One was the Traditions E-bolt 209 which fired when closing the bolt (from his previous muzzleloading video 21st Century Muzzleloading). The only one from Secrets was the Remington 700 which send sparks into his face and onto his arms. That was with 2 different test guns. The first was sent back to Remington. Both videos are worth getting. The first one had: Knight Disc Extreme, T/C Encore, Traditions Ebolt 209, T/C Omega, Winchester X-150 all in .50 caliber. The second one has: Remington 700, Savage 10ML II, CVA Optima, Traditions Evolution Premier, Knight Disc Elite, White 98, Austin & Haleck 420 with the Knight, Traditions, Savage, Austin &Halleck, and Reminton in .50 caliber. The rest were .45's.
I'm just scratching the surface here. He did blowback tests on all of them. You'd be surprised at the results. Really if you're interested in muzzleloading, he does more than just test guns. Scopes, accesories, bullets, powders, primers, even some chrono's and breach plug grease. Both videos combined will teach you more than you'd learn at your gunstore just looking at the guns and accesories. The gun reviews alone pay for the videos if they steer you clear of the problem guns.