Doco Overboard
Ultimate Member
Odd fact: my large frame AR in .308 runs more reliably suppressed on a lower gas setting with steel cased ammo than it does with brass cased ammo. Not sure why that is.
Next time you have cause to think about it, or if you even care to do it, check your (brass/ steel) cartridges with a protractor before and after firing and use a comparator. Especially the sharp angle at the shoulder neck juncture.
What you may be able to determine is that differences in the sharp shoulder, (brass vs. steel) have a pronounced effect on pressure and internal ballistics. These same characteristics also have a degree of influence on throat erosion and were a concern for wildcatters and early developers of high velocity cartridges. Not that they used steel cases but you get the picture.
In your rifle, all that may be happening is that the steel cased ammo does not have the elasticity of brass and the turbulence of the expanding gases reacts differently with the steel case, at the steeper shoulder angle, than the brass, working with the lower gas setting more reliably as the gas is moved forward towards the case mouth, the bore and until the projii is clear of the entire vessel and could be partly responsible for your observation.