Wow. The previous page caused a torrent of emails and posts to Mark's Live Journal. (Or what passes for a torrent around here, anyway.) They were all wondering why firing that gun on page 134 didn't send our friendly neighborhood goon flying backwards in great pain. Well, the answer is in the word "if" on page 135. "If I set [the gun] to 100% power," he says. The gun was set to low power at that point. On this page, he sets it to 100%. In the last panel, a 0.9 kg mass is launched at 1 km per second. The panel is blacked out, to maintain suspense.
However, if you don't like suspense you're welcome to do the equations of motion for 900 grams accelerated from rest to 1000 m/s in the length of that barrel and see just how stupid the neighborhood goon is being. I know I did the math, before I wrote the script. The word we're looking for is "extremely." The goon is being extremely stupid.