Quietest 300 BLK Subsonic Round for Daniel Defense M4 ISR

[mxjoe35]

Ok, I purchased a Daniel Defense M4 ISR. https://danieldefense.com/firearms/dani ... ec-tm.html I then went out and bought some Remington 220gr subsonic rounds. When I pulled the trigger the first time I was a bit shocked at how NOT QUIET it was. It did sound like a .22 going off, which yes is quieter than a 300 BLK, but not as quiet as I wanted it to be. So my journey begins to find/develop the quietest possible round for my rifle...that is still strong enough to take down a coyote.

First step watch a 1000 videos on reloading and presses. I decided on the Hornady LnL AP, well because it's a good press and I had $425 in rebates at Cabela's!


Second (Sunday) buy the press and build the bench:


Third (Monday-Tue) set up, calibrate and build your first round!


Fourth (Wed) start building recipes:


Hodgdon Lil-Gun
Hornady Interlock 165gr

My theory is that to push a 220gr round at 1050 fps takes more powder than pushing a 165gr or a 150gr bullet at 1050 fps. So less powder, means less BOOM...meaning less noise. (Makes complete sense in my head! lol) Now I know there is a balancing point of slower/lighter bullet and not cycling the rounds properly. I am also aware that I could put in a lighter recoil spring to allow for lighter rounds. So there are a whole bunch of variables at play, which will give me something to do in testing out different recipes. So does anyone have know light bullet, subsonic recipes for a 9" barrel, suppressed AR?

[withoutremorse42]

I don't have the exact info you're looking for, but here's my take on it.

I've reviewed and compared 4.75", 6", 6.25" and 6.5" barrels with about 10 types of ammo, 4 of which were subs.

Using the same two suppressors for each, the 190 gr discreet ballistics subs (the variety optimized for 7-11" barrels) was noticably quieter than any of the 3 types of 220gr subsonic rounds.

Not scientific testing, just my experience with all 4 uppers on the same range, same day, same ammo, same cans.

Just wanted to confirm your theory that "less powder equals less boom" when moving a lighter round.

[BoomerVF14]

Wasn't mentioned in the OP, but you ARE using a chronograph, yes?

And BTW, your bench construction assistant is pushing the cuteness limit for a forum such as this

[bangbangping]

Warning: I am not going to directly answer your question.

In my humble opinion, if you plan to hunt subsonic you should stick to a heavy bullet that is known to expand at low velocities. If you want super quiet, get a bolt action with a 16" barrel. A 9" AR, especially if you want it to cycle, will never be stealthy. That said, you certainly can get quieter than Remington factory ammo.

Do you have a chronograph? They're pretty much mandatory for loading subsonic. Load down to 950-1000 fps and you'll notice a definite improvement in the sound level.

[mxjoe35]

So my helper insisted that because she helped me build my bench ( handed me screws), she got to be in the picture! I am getting my chrono next week. I also bought a db meter, so there will be no guessing which is the quietest. Hopefully next weekend I'll get to do some testing.

[John A.]

One small recommendation.

Test the bullets without the suppressor to ensure stability before shooting them through the can.

You can always make extras to check how they sound through the can, but one of the most important thing about reloading is to check the bullets first and foremost. Otherwise, it's possible that you'll be walking down range trying to find all the piece to the silencer after it blew into pieces. At that point, no one will care how quiet it wasn't.

I went down the same path you did because I too was disappointed in how the blackout sounded. It was down right disappointing and I've been into suppressors for a really long time and knew what "not quiet" sounded like, and that was what I noticed right off. I always compare it to the sound of garbage can lids banging together.

[mxjoe35]

Great tip! My suppressor is permanently attached to the barrel, making it a single tax stamp gun. So I can't take it off, but I can remove the baffling and end cap. Am I just looking to make sure the rounds fire and don't keyhole at close range?

[John A.]

Yeah, removing the baffles and front cap and you'll be golden.

It's just that I've seen a few baffle strikes and I'm sure neither of us want to go down that road while testing a new load.

[2manyToys]

The quietest powder that I've used in both 8 and 8-1/2" barrels has been Vihtavuori N105 and Blue Dot under 190 to 245 grain bullets. I did have to open up my gas gas port to get it to cycle. You will still have ejection port and action noise that not much can been done to squelch. N110 and N120 are easier to get to cycle, but are louder.

[dellet]

Working with subs can be counter intuitive at times. Lighter bullets generally speaking will have more unburned gas and powder along with higher muzzle pressure. All this creates noise. Some at the muzzle some at the ejection port. For instance a 125 grain subsonic load leaves so much gas behind to get the action to cycle, it’s much louder than a 265 grain load.

Faster powders behind heavier bullets, in general will have a more complete burn, higher peak pressure and a lower muzzle pressure. This means a cleaner burn, less noise to mitigate at the suppressor, less blow back and less noise at the Shooters ear, out the port.

Then certain powders are just quieter. Mass of powder has very little to do with actual noise, other than faster powders that burn more completely generally also take less powder.

There are a ton of trade offs, suppressor design, back pressure created, bullet construction and material. With some effort some really quiet loads are possible.

This was a couple years ago and is a good place to start.

viewtopic.php?f=128&t=98869

But new things are discovered all the time, so some info might be dated.