Tried finding some YouTube videos that may address this, but was overwhelmed with the non-specific content to this specific question.  Hoping there is some guidance here.

I just bought a Sig Rattler 300BLK upper.  I wanted a short, piston upper so the gas would go further away from my face.

I already have a SiCo Saker 7.62, but man is this a heavy and long kid.  The Sandman K looks like a very attractive option for these very reasons.  Obviously the Saker would be quieter, but with 220 Sub's, how realistic would this be to not have to use ears when shooting with this combination?

I've never shot that combination, so I'm going to guess it'll still be pretty loud to the shooter because of the washback effect from the muzzle sound.  An ideal setup for this would be a Nomad-30 or Nomad-Ti.  This what I've shot on this platform and it's amazing.  If you direct thread the suppressor on, then you're looking at about 5.9" added.  That's a couple more than the -K, but the sound difference will be astounding.  If you want absolute muzzle suppression then the Nomad-L or Nomad-LT is the way to go, but then you're departing from the super compact concept you're targeting.

Todd Magee
Dead Air Engineering

sandman K is not very quiet, even with subs.

It won’t be quiet
And without googling, I have a hard time believing a sandmanK is that much lighter than the Saker

Most of the gas blow back comes down the bore from gas capacitance in the can coupled with fast bolt unlocking.  Piston guns frequently unlock faster than gas impingement and tuning a piston for slower unlock usually involves noisy high pressure venting at the gas block-piston coupling.  Suppressed, my piston uppers don’t shoot any cleaner than gas impingement.   They do keep the receiver cooler though.  The Saker can be very quiet on a tuned gun, but it’s construction is much heavier than needed for 300 Blackout.  If you can’t tune the gun something with a larger bore and volume could be optimal.  Tuned, something like an Ultra 9 or Thunder Chicken/Full Nelson is light and quiet. With subs backpressure can help when the gun gets dirty. The Sandman K (And similar short designs) is a good fit where length matters and the objective is to try and take the edge off.  It’s overbuilt for most 300 Blackout use but with a flash hider front cap would be nice for wanton full auto.

I run a SIG SRD762Ti-10. It's a great combo.

Something Ti and direct thread @ 1.75ish diameter is what you need. Something with volume but light.

My Sandman K should be approved in about two weeks, and I can let you know.

I'm planning mostly on supers for it, I have a Saker 762 and a 762sdn-6 for it if I want it for subs.

I run a Sandman-K on my .300blk Rattler. When shooting  subsonic ammunition without hearing protection, this combination is not hearing safe or particularly enjoyable. For me, the Rattler/-K combination checks all the right boxes when shooting supersonic ammunition.

Im still running an AAC 762SDN6 on my Rattler. It's long and heavy but cycles the Hornady 190s and 208s just fine and I don't get any blowback or need to wear Earpro so...

On the other hand, OP, have you looked at the Rugged Micro30?

Have you tried supers with that combo?

I'm in line to get a Keymo on my 762sdn6, and I asked if they could do anything with a stronger blast baffle. Ecco basically said that it should be strong enough for some supers, probably not a steady diet though.

Why wouldn't an SDN6 be strong enough for supers?

Or is it the keymo conversion that isn't strong?

Word. the N6 was designed around 12" HK417 in .308. So it's plenty strong enough to handle .300 BLK supers.

I thought it wasn't rated for a 5.5" .300blk barrel. I'm seeing 7" as what it's rated for in .300blk.

If it is, that'd be great.

Rattler + Sandman S+K owner here.

Unless your hearing is already rekt, shooting subs + suppressor out of the Rattler isn't pleasant for more than a few shots.

YMMV

Done subs and supers from a Sandman K in a rattler. Supers threw flash and were unsafe loud. Subs were just painfully loud. Honestly the can isn't worth it on the Rattler. I'd rather just use bare muzzle or a larger volume can.

Funny thing is I've only been shooting my Rattler/SDN-6 with the Hornady 190 Sub-x or 208gr A-max rounds, as that's the set up I intended it for.  I'd have no worries with supers through that barrel/can though.

Cool. I'm looking forward to having that as an option.