Been told by several who built 300 BO pistols go with a 7.5 inch barrel, if you plan on running a suppressor.
I wouldn't consider that good advice at all. Stick with at least 9" or longer, ~10.5" is better. The very short barrels are a LOT louder, both suppressed and unsuppressed, and are also more finicky about ammo. Also, while the 300 is pretty efficient down to about 9" of barrel, you do give up a lot more with barrels shorter than that.
I've had good results with 9" and 11" 300 Blk pistol barrels, if I were starting over I'd stick with about 10"-10.5".
