For BB's 1632 Red - Either single tubes (with a small micrifibre pouch - similar to Liquid Bullet pouches) or with a frame that accepts looped tubes 200-210mm in length with a 50mm pseudo. This is what I do almost 90% of my shooting with. The setup will also handle 6mm steel.
Awesome!! The best flatband I've ever used. A little bit whiter than shown in picture, great elasticity. Thank you Dankung for another great product.
For 9.5mm steel I like 1842 black either in single or with 1/3 taper - this also works for hunting if thats your thing.