Thread: Subsonic 300blk suppression issues

Hello all, I’ve got a howa mini 300 blackout, I’ve shortened the barrel to 14”, got a load that’s very accurate and subsonic (190sub-x, converted 223 brass, once fired in this rifle and resized, win 296 powder). My problem is it’s still pretty bloody loud, certainly more so than I was expecting. I’ve tried three different suppressors (brand new dpt, sonic ghost 40, and another larger diameter sonic), I’ve tried getting the loads way down to 700fps, several different projectiles at 900ish fps (all speeds verified with a chrono, definitely not supersonic). The only other thing I can think of is the dies that came with the rifle are rcbs small base, perhaps after FL sizing some of the gas/noise is exiting out the pressure relief hole on the left side of the receiver, I think I may be clutching at straws here but that’s the only thing I can think of.
Am I just expecting too much out of this round/suppressors? I was expecting only slightly more noise than a 22 but it’s more like a 22mag.
Any light that could be shed on this situation will be appreciated even if the outcome is that I’m a moron than expects too much!
Cheers!

I have a 338br throwing a 300gr sub at 1150fps. It's quiet enough. Depends what environment it is being shot towards

The problem might be the powder you're using. Win 296 / H110 is quite slow burning. Slow powders are used so that there's as much gas as possible to help cycle the actions on the likes of AR-15's. You can get away with using much faster burning powders, with a bolt action. I used AP70, AP100, and Alliant Red Dot which were all very quiet.

Thanks Pommy, very useful info, I was under the impression that 296 was fast enough. I’ll get my grubby little mits on another powder and keep the win296 for super loads when I get around to them. Of the powders you mentioned above have you got a favourite for subsonic blackouts? Or anyone else have any first hand experience?

The noise is breaking the sound barrier by the speed the projectile is traveling, no?

I have similar issues with 2205 16 barrel 9grns with 200 grn proj I think I need a 12in barrel as same load was great in a 10.5 ar15 . maybe the longer barrel increases pressure to much . Maybe not enough pressure to expand case and seal gases in .

Larskramer, Negative, these loads are all subsonic, verified with a chronograph.

Probably Red Dot. I used 5 and a bit grains with the Sub-X. Be very bloody careful with pistol and shotgun powders though - there's no load data to follow.

Make sure you've got realistic expectations. It's never going to be as quiet as a 22lr when there's at least 5x as much powder going off.

This was the conclusion I was coming too, might be worth trying to neck size only some fired brass. But like Pommy said, perhaps my powder choice is a bit on the slow side. Experiment time I think!

Thanks again Pommy,
The reason my expectations are a little higher is this rifle is a lot louder than a mates 16” 308 running subsonic factory ammo (Winchester I think) running a dpt with only two baffles. The dpt I tried today was brand spanking new with all the baffles (4?). I think you maybe on the money with the powder burn rate. I do however realise it’s never going to be 22lr quiet.

4 baffles in my subsonic .45 was loud, 6 baffles is a lot better.

This may not be relevant, so feel free to ignore. I was using Hornady Sub-X factory 300BLK rounds and they were louder than anticipated. Pretty sure some were going supersonic, but that wasn't the whole story.

I got a carbon stealth suppressor on mine with running 190 sub x and shes quiet as a sleeping baby. Can had a big part to play in it

I am shooting the factory sub x in mine most of the time now.
But prior to that I used to shoot the 240 gr SMk.
From the beginning I added two extra baffles on my Dpt.
That did improve the noise. Up to 8 baffles total, you will notice the difference, from 8 to ten the improvement is not so noticeable.
Another thing would be to try a lighter bullet, like the 151 gr cast from Robert ( shooternz on this forum).
The physics of it are :
For a same speed ( ie around that 1030 fps ) you will need less powder to push a lighter projectile than a a heavier one, therefore you will generate less gasses and/or less pressure= a bit less noise.
I have always loaded with vitavuhori n110. The beauty is that I can load subsonic or supersonic from 125 gr to 240 gr.

But yes you could try other faster powders suggested above.

One last thing, shooting in the confinement of the bush makes the sound sounding louder than shooting in an open paddock.

Beware of the ricochet and good luck.

The noise is related to muzzle pressure.
Lighter bullet weights,longer barrels,faster powders will be quieter than shorter barrels ,heavier bullet weights and slower powders.