In my limited semi-scientific experience, DI is the champ.

A friend recently got a MCX Spear LT 300BO pistol with ~9" barrel.

We shot his gun alongside mine. Same ammo, same silencer, back-to-back. It really was back-to-back too, because there were two available identical silencers; we didn't have to swap the can around.

The DI gun had a bit shorter barrel, advertised as 8.3", where the SIG is advertised as 9".

The DI gun was quieter as both shooter and observer. The difference was more significant as the shooter. The first round "pop" as perceived by the observer was quite significant, with the follow-ups also being louder than the DI, but less-so than the difference perceived as the shooter.

Your experience may vary, but if it wasn't at least as controlled as mine, it may not be worth much.

Both men present and involved as shooter and observer agreed on the performance described.

It's worth noting that the DI gun does not have a JP-style "captive, silent" buffer/spring assembly, which is reputed to assist in noise reduction.

Could this phenomenon that is reportedly common with piston systems have anything to do with the difference? I.e., extra gas discharge that is not moderated by the suppressor.

Almost certainly.

I have read online, however, that piston advocates in the suppressed context cite an elimination of "port pop" that DI guns are subject to.

That "pop" happens somewhere else, if it doesn't happen at the moment the gas key separates from the gas tube or when gas vents out the side of the carrier. As evidenced in your photo.

It would be interesting to see by way of condensation signature in cool, damp weather how much difference there is in the gas expelled through the ejection port between otherwise similar piston and DI guns when suppressors are used.

But even if the difference is between gas discharged at the piston or at the gas key, wouldn’t the pressure and perhaps the volume of the gas be greater in a piston system?

Something that’s very common is for fans of anything to tout its virtues and advantages while ignoring the defects and disadvantages of what they don’t prefer. I don’t have any experience with piston systems or suppressors on gas guns, but it wouldn’t surprise me in the least for someone to say, “See, no port pop,” even though higher pressure and greater volume from other part of the system might get no attention whatsoever.

If you want to eliminate port pop, you need a bolt action or other locked breech system. All gas guns, whether piston or DI need to have a place for the gas to vent. That’s part of the design, and a suppressor isn’t going to get rid of that. A suppressor also isn’t going to get rid of the noise from the bolt slamming back home with each shot. Again, bolt action is the solution.

I’m not sure that it’s a hard and fast rule that DI is quieter than piston. It probably depends somewhat on design, ammo, etc. If their 300BO is like their MPX, Sigs are gassy. That doesn’t mean every piston gun will have the same port pop noise as a Sig.

When doing internet searches like "quietest 300 blackout semi auto host rifle" the AI summary always mentions the MCX platform. It also consistently mentions things like the Honey Badger and Maxim PDX-SD. Also mentioned, but less frequently, are things like the DDM4ISR and CMMG Dissent.

So the internet at large seems more-or-less split on the matter.

I guess it depends on tee specifics of each upper. Anything that bleeds off excess gas can most likely have a "gas pop" report that might be loud I had a superlative arms gas block for a while that bleed off excess gas on a DI upper. similar issue as a "piston pop"... i changed it to a riflespeed gasblock where it does seem to have reduced that "pop" especially on the first round.

i have yet to own a "flow through" or low back pressure suppressors, not sure how that changes things, but presume it also helps alleviate that pop for piston or other bleed off gas systems.

quote:

Originally posted by Dwill104:
If you want to eliminate port pop, you need a bolt action or other locked breech system. All gas guns, whether piston or DI need to have a place for the gas to vent.

Pardon my ignorance but has anybody put a suppressor on a H&K?

MP5s have a good suppressed reputation, but they're 9mm.

I have read that the actions on rifle-caliber roller guns are quite loud. I haven't experienced it firsthand.