Recently I have attempted to suppress 10.5" 5.56 AR15 and my god that thing was covered in carbon everywhere but the last round in the magazine only after 5 shots.
I know I could adjust the gas block but still, all that gunk would just collect in the suppressor.

I started looking for possible solutions but could not find a single one.
I see some manufacturers offer an "SBR" variant of .300BLK ammo, why no one offers the same for .223?
It's doubtful people like fireballs, concussions, and gunked guns/suppressors that much...

Is there any data on (Re)Loading .223/5.56 specifically for a short barrel (SBR)?
Can't we work out a load based on .300BLK recipe for .223?

I have the same setup, and experienced a similar issue. I wound up developing a specific load for my rifle using a Hornady 55gr FMJ-BT and 14.4gr of IMR 4227. Seems to behave well enough, chronos right around 2200fps.

.300 BLK was designed from the ground up for SBRs, so this is an apple's and oranges comparison.

In 5.56 SBRs, you're going to have unburnt powder no matter what.

Maybe check out CFE .223 if worried about carbon buildup and cleaning.

Thanks, that's a great starting point.

I agree .300blk is a different beast but since there are different loads for long and short barrels in .300blk why can't we apply the same principles in .223?
I am just getting into the reloading but can't we just use less amount of a faster burning powder?

Because 300 black out mainly uses handgun powders, and 556 uses rifle powders

I use CFE223. I'm not sure how much it actually helps, but my SBR's aren't any dirtier than my 16/18" rifles

I would look at loads with RL10x, AA2200, AA2015 or IMR3031 if you are shooting .223/5.56.

kwg

I've tried a 300 blk specific powder in the 5.56 and the results were abysmal.  I think one load even had a triple digit SD.

You're not going to get the 5.56 quiet. Best you can do is maximize the burn before it reaches the muzzle. I had good results with H335 and magnum primers.

I actually ran a test and posted here on similar - though a suppressor wasn't involved:

https://www.ar15.com/forums/armory/Test-results-affect-of-BBL-length-decrease-on-velocity-with-fast-vs-slow-rifle-powder/42-499814/?page=1

Bottom line, the faster LT-32 (think 4198 speed), is implied to have a relatively cleaner and more complete burn compared to slower powders like CFE223 as the barrel gets shorter; but it wasn't that profound.  That said, for your goal, I'd run something like LT-32, and run it on the warm side; since warmer pressure loads tend to have more complete (less sooty) burns.

The burn science is actually fascinating.  Turns out, the bulk of the powder is actually burned in the first few inches, because that's when the pressure and temperature is the hottest.  The powder grains are essentially immersed in high pressure/high density/high temperature plasma there (peak pressure), so the heat-transfer is very high, causing the burn rate to be very high.  As the bullet travels down the barrel and pressure falls, it sort of quenches the burn rate of the powder.  Weak loads never achieve peak pressure, so the burning grains aren't immersed in as vigorous of plasma (yea yea, it's not really "plasma")  as they would be in a strong load, so don't burn as fully or completely.  And their reaction rate is even more quenched by even cooler and lower density medium as the volume is expanding by the bullet passing down the barrel.

Result, weak loads are sooty as Hell, and in my experience sometimes won't even sustain burn; even worse-so with a slow burning powder like CFE.  One time I've actually had scorched but not fully lite off squib's that wouldn't push the bullet all the way down the barrel, with excessively weak loads.  That's a pucker-inducing discovery: trying to do ultra-safe ultra-light loads actually was dangerous as Hell, but I digress.

That science also can explain why some powders once you hit peak, get get scary spikey.  And why even a little contamination with pistol powder can get scary fast (the hotter burning pistol powder can bootstrap the should-be-slower burning rifle grains around it).

What kind of gas block are you using?

I’ll second kwg; RL10x is one of the cleanest powders I’ve used

I use a Faxon 10.5" with Carbine gas port and adjustable gas block set to run with a lightweight BCG and buffer.
There are no function issues with the firearm (with and without suppressor), I just wish there was a magic load stop "dumping" of an un-utilized powder in form of fireball or soot.