I too got a garbage riveter at harbor freight which I returned. I then bought one at Home Depot for a little more which works better but not perfect.
After reinstalling 3 windows
by myself, I've got a few tips: always hold the rivet gun perfectly straight on the stem, if it is angled it will jam inside; use a bit of WD 40 on the internal gears, helps immensely with the effort required for female hand strength to close the gun and break the stem and keeps parts from locking up. And if it gets stuck, I used a long nail to pound out the stem and then pull out the nail. Works better than dismantling the gun each time. For my first window, I did that plenty!
I also upsized the rivets to 3/16, mostly because I couldn't find the right length. The 5/32 were not long enough. Upsized required making each hole slightly bigger with a drill bit, but It fits snugly and forms a tight seal with the butyl. The old, smaller ones had leaks
and the butyl tape had all but melted away. The3/16 head is a little bigger, but again should never leak, at least not for the next 30 years. Glad to cross that project off the list!