My guess is they may not be used to hearing a .223 without a flash suppressor. The suppressor does drop the gas temperature some, and it directs the gases, both of which could affect report. If the muzzle blast is extra loud, you could also be burning powder inefficiently, making a lower peak pressure and forcing you to use more powder and make more total gas to get the velocity you have than would be the case with better ignition.
H335 is one of the old spherical formulations that CCI reformulated their magnum primers to improve ignition of in 1989. So if you are using standard primers with it, I would go to the CCI #41 primer. It is a military sensitivity primer for added slamfire resistance in the AR action, and they are magnum spec. If you can't find them conveniently, the CCI 450 small rifle magnum primer would be my next choice just because it employs that same magnum formulation that is specifically geared toward that kind of powder. Seat firmly for most consistent ignition.
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