I have repurposed east german army backpack as bicycle panniers a few weeks ago. It was time to test them. Unfortunately, our 3 days road touring trip changed to 2 days road touring trip and finally became a 40km day ride loaded with pannier. Weather was not on our side.
Nonetheless, i loaded the bike with regular touring load but this time with my smaller repurposed army backpack bicycle pannier. They are supposed to be about 21-22L (10-11L/each) so a lot smaller than my previous 38L one. Surprisingly, they took the same amount of gear. My sleeping bag and sleeping mat were in my under stuffed rear 20L drybag. The same bag could take easily a fall -5C down bag + sleeping mat + ultra light Montbell down jacket.
I have sewn an extension collar (watherproof silnylon) on the ride side. It took all my clothes (mild end of summer temperature) with room to spare. They could take my fall-spring setup without problem.
The left side doesn’t have an extension collar for now. I don’t think it will need it. This side took the tent, ground sheet, cooking set, emergency kit and a few more small things. It was almost full.
We got rain. Everything staid perfectly dry. It seem those east german backpack are watherproof or at least very weatherproof. I think i will like top loading touring pannier a lot more than panel loading one. A few stuff sack keep everyhting grouped together. Adjustable strap adjust the load volume.