Subsonic

[BRDN]

So I’ve been scouring the threads on subsonics for days now. I have more questions than answers now😎
Anyway, it’s my first ar 300 blackout. 10 inch barrel, suppressed. A 150 gr bullet over 6 grains of trail boss is whisper quiet. However, my Lee 230 gr cast PC boolit over 7 gr of lilgun is not! It is subsonic, but no where near as quiet as the 150 gr Will going to a faster powder (similar to tb) get me down to whisper with thee 230 gr boolit?
And, which powder?

Thanks,
Don

[Kestrel4k]

I have found specific chrono numbers useful in suppressed tuning loads for noise; what are you getting with each load ?

[popper]

Lilgun only burns 50% of your powder in a 10" barrel. Way too slow. Try 2400 or unique.

[405grain]

Bullseye, Red Dot, Green Dot, Unique. Use a powder that will finish the combustion inside the barrel.

[charlie b]

Keep in mind I don't own a suppressor. But, I have fired a bunch of subsonic loads from a rifle (and I might have stayed in a Holiday Inn ).

The above is good. Faster powder is better. I'd use the fastest powder capable of getting up to speed and still under max. This is where longer barrels are more flexible.

Larger bullets at same vel with same powder will be louder. Takes more overall 'pressure' to get them to the same speed. That extra pressure is like popping a champagne cork. Don't know if this is the same with a suppressor.

Last, are you sure you are subsonic? The transonic zone is 'wide' and atmospheric changes cause a slight difference in the speed of sound, especially temperature and altitude. That and 'book' velocity values are not always what you get in your gun.

[jcren]

All good answers, faster powders burn inside the barrel and have less of a muzzle blast when the bullet exits. I use a lot of red dot for subsonic, but some powders are also quieter than others at a given velocity. Unique and cfe pistol are much lower toned and sound mellower than bullseye or autocomp.

[BRDN]

Thanks for the good advice. I have chronographed them all and so far everything is under 1050 fps. Faster powder it is!!

[BRDN]

Fascinating. Loaded up the 230 gr boolit with 6 gr and 6.5 gr of Universal (closest thing I had to Unique). 970 fps. Very quiet, but very unstable. Boolit tumbles.

[Iron369]

I use 10.8gr of Accurate 1680 under a 220gr lead projectile in a 8.5” suppressed sbr ar15. It’s quiet enough to make me giggle every time.

[popper]

Super vs subsonic bullets make little difference in the bang at the muzzle. Even a subsonic 'load' produces a supersonic gas shock wave at the muzzle -- that is what supressors try to eliminate. Push gas through a hole, smaller hole = higher velocity. The 'hole' is the space around the bullet when it leaves the crown and where an imperfect base causes poor accuracy. Probably has the most effect with bullet damage in the bore second.

[Finster101]

I'm using 9.8 grns of Accurate 1680 with a 7.5 inch barrel and 230 grain boolit in an AR pistol. Very quiet and runs the gun well including locking the bolt back. I have tried several other powders for subs but keep coming back to 1680.

[GhostHawk]

I have shot .357 mag loads with 158 gr bullet over 4.6 grains of Red Dot that were quieter than some .22LR I have shot. No suppressor involved.

They are just plain quiet.

Increasing bullet weight is going to increase pressure which will increase noise.

So I would go back to the 150 gr, pick a fast powder with a moderate charge and see what you get.

Red Dot is amazingly quiet in most of my riles. And it does not need a lot of barrel length to do it in.

My .444marlin Handi rifle actually has a doppler effect like a slide whistle. Starts low and zips high very fast. But no loud crack or snap.

[Finster101]

I did not see it mentioned, is the OP using a suppresser?

[BRDN]

I’m using the powders I have before I buy more..��. I tried Accurate no. 7 today, 10 grns, it shot very well but 1320 fps. Tried 7 and 8 grains of longshot and more tumbles.
Thanks everyone for the advice. Tomorrow I’ll lower the number 7 and try Clays and 2400. If that doesn’t work out I’ll make the drive for the red dot and 1680.
Thanks everyone,
Don

[BRDN]

I did not see it mentioned, is the OP using a suppresser?

Yes

[charlie b]

I’m using the powders I have before I buy more..��. I tried Accurate no. 7 today, 10 grns, it shot very well but 1320 fps. Tried 7 and 8 grains of longshot and more tumbles.
Thanks everyone for the advice. Tomorrow I’ll lower the number 7 and try Clays and 2400. If that doesn’t work out I’ll make the drive for the red dot and 1680.
Thanks everyone,
Don

That's one of the problems with the heavier bullets. You are on the edge of stability so you have to load just below the speed of sound. Just a matter of finding the fastest powder that will get you there without too high a pressure.

The lighter bullets are shorter so they will remain stable at a lower muzzle vel.

[mehavey]

Clays will be near as faster as Red Dot.
It should satisfy your reqm'ts for complete burn before muzzle exit.
Doing it in a 10" barrel.....

But tumbling due to insufficient speed (actually bullet rotation/rpm) will still be a breaking point.
(Running the calcs, though, a 150gr Sierra/common nose design at 1,100fps/10-twist "should" be stable)

[Finster101]

My experience is that most short 300 BO barrels are 1 in 7 or 1 in 8 twist. Stabilization should not be that big a problem.

[BRDN]

Had a great day loading, shooting and learning. The subsonic realm is addictive��. For the 230 gr boolit I used Clays, Trail boss, Universal, no 7, 2400, lil gun and reloader 7. I shot from 600 fps to 1300 fps. In the end the trail boss was the quietest. But I could only get 7.5 gns in the case and it was compressed (850 fps). The clays (7 gr). 1100 fps shot great. Universal wouldn’t stabilize the boolit at any speed. Accurate no 7 tumbled also. Reloader 7 was on a whim, too loud.
In the end the clays, 2400 and lil gun shot the best but I really couldn’t tell any difference in the sound. It’s quiet enough with the suppressor to not need hearing protection but nothing like shooting a 150 gr boolit. I’m going to move down to a 180 gn boolit and see if I can get it to whisper like the 150.
Thanks folks for your help,
Don

[mehavey]

trail boss was the quietest. But I could only get 7.5 gns
in the case and it was compressed (850 fps)

Never compress Trailboss....