what ammo are you using?
have you tried other mags, or does it happen with multiples?
have you tried a different lower?
or even just a different bolt/bcg from another upper? (any standard 223 bolt/bcg will work, although a full auto/m16 style bcg is recommended due to the bit of extra weight)
generally with a pistol configuration you need a H2 buffer to cycle properly with the 300 blk.
modifying things so that the bolt travels faster is not going to be helpful.
a h1 & carbine buffer are both too light and clipping any coils off the standard spring is only going to make things worse.
since its not kicking the shell out, as noted above checking the ejector is going to be a solid place to start. i would also suggest looking for any burrs on the extractor and check the spring there. you'd see nice big ugly claw marks on the case rims if the extractor is marred up.
modifying the gas port should be an absolute last ditch effort if *NOTHING* else solves the issue. rarely - if ever - is this necessary on a pistol gas configured barrel these days. peel the clock back 5-7 years and it was more common, but most manufacturer's have solved it and your 0.086 0.089 (sorry typo, corrected) seems about right, if not a bit on the large side.
general rule of thumb for blackout (with adjustable stock) to operate in all 4 configurations (suppressed subsonic, suppressed supersonic, unsuppressed subsonic, unsuppressed supersonic)
rifle barrel, carbine gas = carbine buffer and standard carbine spring
pistol barrel, pistol gas = h2 buffer and standard carbine spring
if you have a pistol gas setup on a 16" rifle barrel you'll probably need to go to a h2 AND an adjustable gas block, especially if shooting suppressed supersonic loads. that configuration with supers tends to be reeeeeeeeeely over gassed due to dwell time and the port being (relatively) far from the muzzle.
hth