Here are two washer like pads that the Gen 1 and 2 BRN-180s can use. The stock rubber washer does not stay in place very well. This uses the stock screw without the washer. Make sure you print this from ABS or nylon so it holds up to the heat.
The Charmer- 3D printed pic rail charm holder
CMMG .22LR Mag Capacity Limiter
BRN-180 Charging Handle Nub