I am currently waiting on a package and the funds necessary to complete my first two cans, a 9mm and a 22LR.

Assuming these go well, I was considering building an integrally suppressed AR, either in 9mm or 300 BLK.

The general idea is a baffle stack inside a tube (standard suppressor), threaded onto the barrel. However the tube would have a series of holes drilled in it that would expose the expansion chambers behind/in-front of the baffles.

This suppressor would be housed inside a larger tube, maybe 3 or so inches in diameter, acting as a handguard, threaded onto the receiver, similar to the picture down the page in this thread: http://www.silencertalk.com/forum/viewtopic.php?t=50336

The larger tube would act as a secondary "suppressor" , if you will, by (in theory) further slowing the expansion of gases and adding a substantial amount of additional volume. Maybe the outer tube could also have some steel mesh or something in it to act as a sound dampener.

I am not a suppressor designer, I was just thinking about this at work the other day and was thinking it would be cool to have a 300 BLK that sounded like a 22LR, if possible.

The picture in the link I posted is what gave me the idea. A long suppressor with venting holes inside a larger tube seems like it would be quite quiet, though somewhat long and bulky.

Can anyone give any advice on this design? Is there any reason this wouldn't work? Or will I be dissapointed?

My goal here is to make a (300 or 9mm) rifle as absolutely Hollywood quiet as I can. Why? Because it would be freakin' cool.

A couple things of note:

-You don't want to slow the expanding gas, you want to give it as much room to move away from the boreline, and expand, before exiting.
-What you're describing is called a reflex suppressor. The concept is sound and not remotely new. Do a google search for inspiration.
-Be careful of fire rate; your hand is holding onto that piece of metal which is grabbing all that energy (heat).
-Whether it be 9mm or 300blk, you'll need a way to seal off the receiver/barrel nut.
-If you go 300blk, you'll need a gas block and a way to seal that off as well.

I didn't click your link, but I'm sure I've seen it.

I thought a reflex suppressor was one that extended back over the barrel to reduce overall length. That isn't really what I was envisioning. Perhaps I should draw something. My paint skills are weak though lol.

Can anyone comment on how much volume contributes to sound reduction? I realize that after a certain point you get diminishing returns, but I would think that a 3 or 4 inch by 17 inch diameter tube would provide considerable suppression potential.

OP you are describing a Gemtech MK-9K design. Do a Google search for images and info.

You described a can that threaded onto the muzzle and was housed inside a larger tube which went BACK to the receiver, which would act as an additional chamber for expanding gas. That is a reflex suppressor. Personally, I wouldn't use anything over 2"OD. Also, be smart w/ your material choice. 2"x.065 x17"LG tubing will be 2lb for steel, just over  pound for Ti, and about 11oz for Al (that's just the tube). A larger tube also lends to larger internals, further increasing weight.

Really evaluate what you're trying to accomplish. A typical design may fulfill your needs w/o being too obtrusive.

I think he's referring to porting the suppressor tube to vent into the secondary tube. essentially a huge coaxial design.

To the OP I too am not a suppressor engineer but I have played with mine and the first thing that comes to mind is that sucker is going to get HOT!!! Remember the #1 purpose of a suppressor is to trap and cool expanding gasses. that heat has to go somewhere which is going to be into your hand!

however you could potentially do some cool double walled argon filled tube (think yeti) between the exterior of the handguard and the secondary suppressor tube. but I think that would only buy you time before it heat soaks. heat tends to radiate outward.

if you do choose to purse said design may I recommend brass eyelets as the medium to fill the void. they tend to hold up pretty well and do a great job of absorbing heat and redirecting flow of the gasses.

One last notable mention. if you do all of this work on the muzzle end you have to remember your efforts may be negated by the ejection port/gas tube as in a semi auto noise at the ear is often higher than at the muzzle. so if your after Hollywood quiet then I'd suggest going to a lock breech design (break action, bolt action, straight pull AR, ect....) and if you want it silly quiet put a wipe or series of wipes in closer towards the end of the can.(this can hurt accuracy though)

You could even get a howa or similar barreled action (don't know if they do 300blk) then build it into a "pistol" to keep the over all package size down. running single shot specific loads will also be quieter. ie. using fast pistol powder vs aa1680 and the like that gas guns need to cycle.

With a rifle caliber (or high volume pistol) that is going to get very, very hot....

Action noise is the problem.   Lots of great 7.62 suppressors are available and they're pretty much all limited by action noise.

You may be disappointed because an ar will never be Hollywood quiet.  You can't get rid of the action noise and port noise.

To get Hollywood quiet you need a repeating rifle (i.e. Not a semi auto) and hand loaded ammo.
Lever actions are all the rage these days, but it's very easy to build an integral silencer on a bolt action barrel.

If you insist on a semi auto, at least get a delayed blowback or gas gun that doesn't vent gas.
There's a reason mp5 and mpx are so quiet...

With that said when I had a 300blk for fun I ran a piece of 357 brass through the dies and it made a perfect 300blk case but with just a slightly shorter neck. one could get a 357 lever gun and have it rebarreled to a 300 blk rimless. you would just be limited on cartridge length and flat/round nose bullets.

Think it would take more than a barrel to make that happen due to the smaller case head diameter (new bolt, extractor, magazine tube feed bits, etc)

Take a look @ the DeLisle carbine of the 2nd WW, OP.  .45 ACP on a SMLE action.

I think you missed the part about using a 357 mag case thorough a 300blk die. so a rimmed (slightly shorter) 300 blk. the big issue would be COAL. as the action is limited by length. be like a modern 32-20 I guess would be a better example.

https://www.thefirearmblog.com/blog/2012/05/09/interesting-300-aac-blk-357-wildcat/

One could get a henry long ranger in 223 and rebarrel it to 300 blackout and easily build an integral silencer on it.

This!  Thought about doing this myself when they first came out.

Thanks for the replies so far.