A thought experiment/question

[a_s]

So this is what I was thinking about. Basically taking a 16" 300blk pistol length AR barrel and drilling a bunch of holes in the barrel starting at about 10" through 15". A shroud from the gas block to where the flash hider would be. The shroud would be something just inside the diameter of the hand guard. It seems like an easy way to get a 16" integrally suppressed barrel which would not qualify the rifle as an SBR.

Would there be an appreciable difference in db?
Would it need baffles or could it be baffle-less?
Would baffles reduce the db?
Is there something like a volume-db reduction formula?
How hot would the barrel get and would the hand guard be problematic?
What part would need to be serialized?

Thanks,

Depending on the answers I may or may not wander down this road as there is a barrel from YHM that I could buy, but making stuff seems like more fun.

[a_canadian]

First off, the ATF's definition of a firearm silencer:

The term “Firearm Silencer” or “Firearm Muffler” means any device for silencing, muffling, or diminishing the report of a portable firearm, including any combination of parts, designed or redesigned, and intended for the use in assembling or fabricating a firearm silencer or firearm muffler, any part intended only for use in such assembly or fabrication.

I quote this, with the highlighted phrase, just so there's no fuzzy lines around whether or not this is a suppressor. My guess is that drilling ports in a barrel is not in itself considered to be manufacture or redesign which constitutes a 'silencer' according to their definition, but that then enclosing any volume of air around that ported barrel is where one crosses the line and creates a regulated device. You probably know this, I'm just spelling it out.

That said, my perspective is that if you're going to the trouble of making a suppressor of any sort, it's worth making it properly. Merely drilling a bunch of holes (and presumably cleaning them up on the inside so that bullets are not smeared all to heck on the way past those holes) and enclosing some volume of air around them is not likely to deliver a very satisfyingly efficient suppressor. If you're going to all that effort, I'd recommend adding at least 3" of clipped cones ahead of the muzzle, inside that same tube. The combination of a heavily ported 5" section of barrel and 5 to 8 60 degree cones is getting into territory where you'll hear a substantial drop in blast noise with subsonics, while only adding a few inches to the rifle overall. The ports alone will probably take some of the edge off the noise. Some cones will bring it into hearing safe territory, or at least close to that.

[doubloon]

... You probably know this, ...

Since he actually asked which part needs to be serialized I think that's a safe bet.

Not Worth Much Answers

maybe
need? no. better? yes.
yes
yes. more volume + more baffles + small aperture ?= quiet suppressor ... if you're not familiar with it the "?=" symbol means "sometimes equals"
depends on how many rounds are fired through it consecutively and not for me
the shroud ... sometimes ... other times the barrel

[John A.]

Would there be an appreciable difference in db?
No, just porting the barrel and catching those gasses wouldn't be worth paying the tax. It would suck.

Would baffles reduce the db?
it should if you add the baffles past the muzzle--and if they're effective and done right

Is there something like a volume-db reduction formula?
no, too many variables

How hot would the barrel get and would the hand guard be problematic?
It would depend on how much you shot. But it can get hotter than your car muffler and is the same principle.

What part would need to be serialized?
the suppressor tube itself, and also in a visible place that doesn't require tools or taking it apart to see the engraving.

[T-Rex]

I think you'd be better off making a thread on design and doing a pin/weld.
You could always remove the weld, to service, and have the ability to unscrew the endcap and service internals.

Still be a 1 stamper.

[fishman]

Don't pin/weld. It's not worth it. Id much much rather have a pistol brace or pay the $200 for the SBR stamp. Ive made this mistake.

[T-Rex]

I understand your sentiment, but a pin/weld would be no different than the presented integral design. I'd much rather have a pin/weld and use the SBR's stamp $$ for another build. The pistol idea is sound, though.

[a_s]

Thanks for the responses. It gives me something more to think about.