Laser, that could most certainly be true for your can design. The .223 is a very difficult round to suppress because of its high velocity. We would have to know what your diverter and primary looks like as well as the type of baffle, facings, timing (volume) of the chambers, firing schedule, etc. If a can strips efficiently at the onset, the volume requirements decrease down the line. But it has consequences as the heat soak/spotting comes in early and designs like these are best suited for bolt guns. If you are firing a good number of rounds, then you will need volume spread all the way down the armature and the ability to let the gasses travel down the tube (baffle overbore.) Its the age old designer's dilemma. Add to that the issues surrounding the can's back pressure through a host's gas system and another layer of complication occurs. I would say that if your end cap is playing a significant role in perceived suppression, look to the first two stages. Lastly, if in fact you have only shot a couple of thousand rounds through your suppressor, it is not even seasoned. The turbulence found in a filthy suppressor makes a significant improvement in suppression and tonality as well. Also, without incurring hydraulic lock, ablatives used with the right design and caliber can actually drive an outstanding design, significantly reducing dB as well as shortening the envelope considerably.
Vox, whether direct impingement or piston, the gas required for the action is stripped prior to the muzzle. A well designed can does not require a piston, but potentially may require an adjustable gas block. The same would hold true for direct impingement systems, they too can benefit from an adjustable gas block. In both instances, an adjustable gas block's main function is to compensate for over-pressurizing of the gas action which is, in the most part, a result of a high pressure can. Having said that, dB should remain un-effected as, if one stops to think about it, the gas for either impingement or piston systems is tapped prior to the muzzle and therefor the can. Lower pressure theoretically from the exiting of gas prior to the can would improve dB suppression (blast) at the can's exit into the atmosphere. When one remembers that gas tapping for integral systems do the same (ss -> subS) , one can see that positive things occur when we reduce pressure prior to suppression. It may however increase action noise (overpressure) and increase chamber pop....read on.
The reason for adjustable/switch gas blocks have become popular, and rightly so, is three fold 1) keeping the action gas pressures within spec when high pressure cans are deployed 2) directly decreasing the amount of propellant blowback in the operator's face (direct impingement) in some actions 3) affording by design the ability to turn off in its entirety the action. We saw the first examples of the operational use of the 3rd point in both the M1a and FN LAR (reversing the grenade launcher gas block/sight in the later) years ago. When one thinks about it there are only five sources of sound to be found in firearms 1) Blast 2) Sonic projectile signature 3) action noise 4) terminal impact of the projectile and 5) operator induce noise. #1, #2, #3 all are suppressor centric. Lastly, your comment about subsonics. Subsonics have real consequences on range, terminal force, accuracy and potentially the functioning of the host. Subsonics can create serious issues for suppression as well (baffle strike) and, dependent on propellant, debris. Having said that, "factory ball ammo" as you call it is not negatively impacted by suppression and can be enhanced in a number of areas.
