Funny you brought up 300blk - I'm waiting on tax stamps for a SBR w/ a muffler in 300blk.
It's a Spikes Tac Compressor, so we'll see what it's like once I get my stamps-so far all I know is it was pretty to look at while filing for it.
I'd like to know how you like that - looks REALLY nice. I considered one, but Spike's wouldn't sell without the silencer, so I decided to just swap out my 16" barrel on my existing 300 BLK. The Efile on the SBR took about 4.5 weeks, but wasn't too bad - literally got it last week!
I need to still sight in my scope on the new barrel. Here is my current build:
300 BLK: Seekins MCSRv2 10" hand guard, 10.5" stainless 300 BLK barrel, Spikes Upper w/ BCG, LMT Lower, Magpul STR, Thunder Beast 30P-1, EOTech XPS2 (or a Burris 3-9x)
Today I put the Carrier Comp Titanium Ext Mag on my Benelli M4. Looks nice and frees up some weight for the Silencerco Salvo I have coming due in around February. I had my 12-yr-old daughter using the infrared thermo to check temp, while my 16-yr old son used a heat gun on the receiver - - while I was cranking on the old magazine to get it off - wasn't easy - Benelli put a crap load of lock-tite like stuff on it.

I purchased that shotgun about a year ago and have used it for anything and everything - its heavy, but with a two-point strap, its fine to walk/hunt/clay with.
Edit: I put a pic up of a couple things I am working on