Stop shooting M193 in a 1-7 twist barrel, and go with a 75-77gr quality bullet, and those 3-4moa AR groups will shrink a lot.A MOA or sub-MOA gun is a gun that can do it regularly and consistently over time until things literally begin to wear out.
Getting lucky with a 3-shot group out of a general purpose AR isn't an accurate judge of the platform's capability - nor the shooter's.
TRULY accurate gas guns are 1.5 MOA guns consistently. Like Knights and Hodge. Note - these are 5.56 guns.
If your BCA or PSA AR-15 in 5.56 is *really* a MOA or better gun consistently over many rounds/mags - then you should prove it. Until then, it's literally not believable because the best of the best doesn't do that.