Is an adjustable gas block even needed?

[SDW]

None of my Grendels have adjustable gas blocks, but I do have an adjustable gas bolt carrier in my 12" pistol, and will be buying Bootleg adjustable gas carriers as my go-to carrier from now on I think.

I had to do a search as soon as I read it. Interesting approach. And it's not even all that expensive at the moment. I think their site says about $180? I watched a couple of videos so far. I'm still unsure how it actually controls the gas. Does it just restrict flow into the... "piston" internal area of the carrier? I don't understand what happens with the unwanted/excess gas yet, but for now I'll assume simply that "it works".

As far as needing an adjustable gas block, I didn't think I'd need one. My Grendel is pure Rifle. A1 (rifle) type buffer system, 20" barrel and rifle gas length. Barrel is Ballistic Advantage. Gas port's around 0.093-ish. I assume that my system produces "just enough" gas to cycle the bolt properly when I use Hdy Black 123gr ammo. All my brass lands in a night little area a couple of feet away, at about 3:30. This is when shooting prone form a bipod. This was after I swapped my recoil spring from a Tubbs flat-wire to a standard rifle spring. FYI, in another rifle the Tubbs spring works great with 5.56. But my Grendel ammo didn't like it, wouldn't cycle fully, so I switched back to a standard spring.

However, this rifle will not cycle the 90gr American Eagle varmint ammo I decided to try. I had to fire these ones like a single-shot---One round in the magazine at a time. They ejected fine but the bolt would not lock back fully. I assumed that the lighter bullets don't provide enough oomph for the recoil system. But could I be wrong here? Could it be providing too much, too fast? The MV was around 2900 as I recall. I still plan to try the 90gr AE ammo in this upper, using one of my carbine lowers to see if that makes a difference. Otherwise, this adjustable carrier might be the way to go.