Brn barrels are nitrided.
If you cut the barrel and use the same gas block, you'd need to open your barrel gas port significantly (somewhere around .090" if i recall correctly) which is made much more difficult than usual due to the nitriding (very hard material destroys small drill bits).
Even if you cut down and got the appropriate 10.4" vented gas block, you'd still need to open the gas port to 1.6mm to work in a factory configuration (HK red spring and red dot buffer).
Or you could cut down, get a vented 10.4 gas block, and experiment with lighter springs and buffers until you get the desired function and not play with the barrel gas port at all .