I went a slightly different direction but got to pretty much the same place...

Mine is 5.56, has an 11.5" bbl and will soon be sporting a brake and blast can though it doesn't really need it because it already shoots extremely nice.

The foxtrot Mike fm15 is also a DI gun just like the cmmg dissent, though I think I like what cmmg is doing with the recoil springs better.

I do question the exact niche the cmmg gun is going for too...

Realistically with the 6.5" bbl and no brace or hinge in it's factory weight spec it's going to wind up substantially heavier once it's actually in usable configuration.

I believe the fm15 11.5 started out around 6 pounds but once I threw on the hinge, tailhook mod 2 magnifier and dot it's definitely not 6 pounds now.

It's still extremely light and handy but it's definitely no feather weight.

I wonder if cmmg did the sling qd point on the rear below the picatinny interface like foxtrot Mike did, that sling point is darn handy

That looks great man.

Stock wise, theres a couple realllly light options.

Personally I'd love to see a Pic rail adapter to use the polymer B&T MP9 stock:

A close second (5.36oz + ~3oz mount) is the JMAC customs SS8:

That should put stocked weight at ~5.3lbs. 

Yeah I'm a fan of the jmac and the mp9 stock would be even better in some cases.

This said, due to the nfa I can't "stock" this gun.

Also, OG tailhooks are completely unobtainable right now which shaded my decision.

(As did the sheer cost and availability issues of my original plan which was to do an ACR brace)

Eventually this gun will get a different ass end but for now this definitely works (other than my dot I bought being 6 inches high at 5 yards when I took it out for initial break in lol)

I am actually coming back to 7.5x27 for cartridge and take it from there. 

graylion said:

I am actually coming back to 7.5x27 for cartridge and take it from there.

Could you be a little more specific?

Well, keep the pocket carbine discussed here, with P-90 style magazine and something like an 8" barrel, but use 7.5 FK

Is this a working gun that you're actually constructing?

nope, I do IT in real life ;) Just playing with ideas.

I'd personally see if you can handle a PS90 in person, or at a minimum the airsoft equivalent.

The top loading mag is cool for the PS90, but its also extremely limiting in its rail space / optic heigh. The magazines themselves are also super wide due to the feed tower, so only 1x mag can be carried per pouch. Whereas a normal box mag can carry 2x per pouch stacked alongside one another. 

A 7.5FK with a basic 30rd mag in the grip format ala MP7/MP9 would be a more practical PDW format. 

I love/hate being a constant contrarian BUT: I can't see the BRNO 7.5 cartridge being remotely viable to any military. 

The 12" Keltec Su16 would be almost as light, and with 77 grainers would be pretty nasty at 100-200m.  Otherwise Tony's old idea for a long barreled "artillery luger" FiveSeven with a wire stock would probably be about as good as one can get.  The difference between the two really boils down to "at what distance do I think non-elite troops can actually hit anything."  I have never had anyone who has actually been in combat state that distance as being more than  100 meters, and I have asked more than a few people. 

The problem with the BRNO or any similar "magnum pistol" auto cartridge is now you have 1) a weapon that is comparable in weight to a lightweight carbine, 2) a cartridge that has equal or lesser """"power""""" to a carbine cartridge, and 3) the ammo itself weighs substantially MORE than 5.7, 5.56, 5.45, or even .30 carbine.  Also your round for round recoil is going to be pretty high. That is 7.5 BRNO is essentially .30 carbine except requiring larger magazines, being heavier, and with higher bolt thrust.

TL/DR: 1939 called, and Carbine Williams wants his ideas back.  From jail.

PPS: I'm trying to be both serious while making myself laugh, in case that is not clear.  Your mileage may vary.