Grendel upper on Springfield Saint lower.

[Sticks]

Of all the issues I have heard of with BCA, gas ports were not one of them. You should be GTG. Do a test fit with the ammo though. You should be able to drop a round in the chamber, turn the rifle barrel up and the round should fall out, or a light tap to drop the round.

Next is chamber a round in the upper only, push the bolt in to battery and it should extract easy and not leave any marks on the bullet aside from a couple of longitudinal scratches from the lugs. Making sure it (bullet) does not get jammed into the lands.