Looking for 300 BO subsonic Load data

[Mac Attack]

Does anyone have a pet load for 300 BO subsonic with 220 gr SMK and H110 powder? I loaded up some 220’s with 8.2 gr of H110 and shot them through my 8.5” barrel SBR upper with suppressor and was not quiet as I had hoped. I hate to keep wasting expensive bullets and losing my brass and was hoping someone already had a good load for me to experiment with.

[waveslayer]

Yes sir. I run 11 grains of H110. I also use Norma 200 for my 8" using 13.5 grains. All loaded at mag length

My wife thinks I only have 3 guns

[LynnJr]

I am running 11.5 grains of AA1680 with the 220's but my barrel is 16.5 inches long.

[sigstroker]

What kind of can?

[waveslayer]

You will want to test your loads through your rifle. You don't want an expensive Baffle strike from a keyhole issue.

There's a ton of data out there but 1680, H110, Norma 200 and CFE BLK have been my go to's as I stated above at those charge weights. The 8" is super fun. I've bow moved to .308 subs mostly

My wife thinks I only have 3 guns

[ar15barrels]

Does anyone have a pet load for 300 BO subsonic with 220 gr SMK and H110 powder? I loaded up some 220’s with 8.2 gr of H110 and shot them through my 8.5” barrel with suppressor and was not quiet as I had hoped. I hate to keep wasting expensive bullets and losing my brass and was hoping someone already had a good load for me to experiment with.

If your load is subsonic, then your can is likely just as quiet as it's going to ever be with H110.
What you can do is move to a faster powder than h110 which will give you a lower pressure at the muzzle.
That will quiet it down more.

Also, go to heavier bullets.
The heavier the bullet, the less powder you can run and therefore the lower the muzzle pressure.

Muzzle pressure is what generates the noise once you are subsonic.
A longer barrel will also lower the muzzle pressure as it will contain the pressure longer and allow you to use a lower charge to get to 1050fps.

Here is H110 compared to AA#5, with both loaded to 1050fps in an 8.5" barrel:


The pressure at the muzzle with H110 is about 5600psi while it's 3600psi with AA#5.

[Mac Attack]

What kind of can?

[Mac Attack]

Here’s a photo of my rifle and video of what it sounds like. Definitely has first round pop. I’m wearing a shooting glove to cover the ejection port and to help deflect the brass because even with an H2 buffer it slings brass and after spending days converting 5.56 brass to 300 BO I sure as hell do not want to lose a single piece.

https://youtube.com/shorts/7Lff_Fw505U?feature=share

[Mac Attack]

Man I need to figure out how to resize my photos! I hope it works.

[Mac Attack]

If your load is subsonic, then your can is likely just as quiet as it's going to ever be with H110.
What you can do is move to a faster powder than h110 which will give you a lower pressure at the muzzle.
That will quiet it down more.

Also, go to heavier bullets.
The heavier the bullet, the less powder you can run and therefore the lower the muzzle pressure.

Muzzle pressure is what generates the noise once you are subsonic.
A longer barrel will also lower the muzzle pressure as it will contain the pressure longer and allow you to use a lower charge to get to 1050fps.

Here is H110 compared to AA#5, with both loaded to 1050fps in an 8.5" barrel:


The pressure at the muzzle with H110 is about 5600psi while it's 3600psi with AA#5.

[ar15barrels]

When I researched powders for 300 BO I saw that H110 was popular and so I bought a lbs. but now I realize the date of those posts was from 2012 range and things have advanced much in the past 20 years and now it seems like AA1680 or CKE BO is the way to go.

1680 is going the wrong way for you if you want it to be quieter.
1680 is what people with 16" carbine gassed barrels have to run to get the gun to function on subsonics.
With a pistol gas port and an adjustable gas system, you can take advantage of faster powders which will give lower muzzle pressure.

H110 is my go-to powder for 300 blackout in both supersonics and heavier subsonic loads.
I have been loading the 300x221 (predecessor to 300 blk being commercialized) since the late 1990's.
It's the cartridge that got me into making AR barrels.
I still have most of a 500 count box of 250gr SMK's that I use sparingly when I want quiet subsonic loads.

[sigstroker]

You can mount a Dead Air can on a YHM mount? Are you using the bottom part of a YHM can screwed into a 1 3/8" thread?

[Mac Attack]

You can mount a Dead Air can on a YHM mount? Are you using the bottom part of a YHM can screwed into a 1 3/8" thread?

Yes you can run a non Dead Air mount on a Nomad 30. Most of the suppressor companies are going the universal mount thread pattern of 1.375x24. That way users who have several different makes of suppressor/mounts do not have to have a special mount for all their rifles. I run YHM muzzle devices on 5 or 6 rifles and the Kurz mount on my rifle cans from different manufacturers. That way I can easily swap my cans between rifles. But my ultimate goal is to have a dedicated suppressor for each of my main rifles and will probably just go direct thread to free up some of the space in the blast chamber that the muzzle devices would normally take up. Extra space in the blast chambers should increase suppression.

[Mac Attack]

@AR15barrels - I loaded few rounds with 10.0 gr H110 at a OAL of 2.250 and they were definitely supersonic and LOUD. Second shot just in case the suppressor needed to fill up first but it was no better than the first. My ears are still ringing. I hand weighed my charges on a calibrated scale so I was exactly 10.0 grains. Any ideas?

https://youtu.be/RB7pu0tjy50

https://youtu.be/yAsLY8eFoMU

[waveslayer]

H110 is fine and isn't old powder. It works really well. Try Norma 200 if you need to as well.

Report back after you get some loads down

My wife thinks I only have 3 guns