hoffmantactical Print speed for the upper was 30 mm/s, nozzle temp was 280 C (turned it down from 290 to help reduce curling), and bed temp of 80 C. It was printed on a Creality K1 that has a printed riser with openable vents to prevent stiff filaments from snapping in the bowden tube.
The handguard was printed with all vents closed at 290 C and no fan. I allowed the chamber to preheat and its temp settled at around 42-43 C or so. Since the SF5 handguard didn't print really any major 45 degree overhangs, it handled these settings perfectly fine. Once I started printing the end cap, the problem of curling when printing 45 degree overhangs appeared. I found that decreasing the print temp to 280 and opening the riser vents to bring the stable chamber temp to around 35-37 C was enough to mostly reduce the curling, but there was still a tiny bit. So for the upper reciever, I added in some fan cooling, I think maybe 10%. That was enough to almost completely get rid of the curling (though frustratingly, I had one upper almost completely finish printing and one of the last support branches curled just enough that the nozzle snapped it and ruined the print). And since the upper is under the tension of the threaded rod in this case, that may be helping offset any reduction in layer adhesion caused by the cooling.
