300 Blackout Sub Load

Stugots

Stugots

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Joined
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Minnesota, USA
I am looking for a subsonic load for the following: 300 Blackout using Starline brass, 150gr Speer boat tail bullets. I have some High Gun (which is suppose to be re-named Hodgdon powder that has since been discontinued. It was a pistol powder I think) powder that I would like to try. 10.5" barrel suppressed. I have heard that Red Dot, Unique and Little Gun are good powders for this but have not been able to find any of it anywhere. Thx.
 
I'd imagine you'll have cycling issues with that light of a projectile for subsonic purposes.

All I've seen for a 150 is with trailboss.

IMG_1364.png
 
N110/120 are good. 120 with heavier bullets cycles most guns fine. I went N110 and had to open my gas port up just a little bit. I haven't made it back to the range to retest since drilling the port slightly bigger. I will then retune my gas block at that point.

Dropping to a 150gr might be tough, you will have to modify the gun around it if its a semi-auto. Light carrier, larger gas port, light buffer setup.
 
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Smokinghole said:
N110/120 are good. 120 with heavier bullets cycles most guns fine. I went N110 and had to open my gas port up just a little bit. I haven't made it back to the range to retest since drilling the port slightly bigger. I will then retune my gas block at that point.

Dropping to a 150gr might be tough, you will have to modify the gun around it if its a semi-auto. Light carrier, larger gas port, light buffer setup.
Click to expand...
Do you have a charge of powder weight in grs you would recommend to start at for 150gr bullets?
 
In my 300 blackout, I'm running 12 grains of CFE black and a 190 sub X projectile from Hornady and I am getting 1040fps. Still in the works though I want to slow it down to about 1000 fps and try to stick with that.
 
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Stugots said:
Do you have a charge of powder weight in grs you would recommend to start at for 150gr bullets?
Click to expand...
I am working with starline brass and CCI450s. My 190 SubX load is still being worked on in the 9.5gr N110 area. Starline brass required me to drop most charges 10-15% to remain subsonic due to its reduced case capacity which is great for subs, but sucks for duplication of existing load data.
 
I also use N110 and IMR 4227 for supers and subs in the 300 BLK. Again, the issue you will likely run into trying subs with a 150 gr will be cycling.

I don't have my Hornady book in front of me, but just look at any 150 gr load and drop down from the min until you hit subsonic velocity. I would worry about case fill though, which is why trailboss was so desirable. It is super bulky and takes up volume even at low charges.
 
Gonna be hard to use that bullet. If quiet is your only reasoning, then drop velocity more using a heavier bullet. There's not a hard line at 1050fps where it goes from loud to quiet. I found that loading 190-220gr for use in a 8.3" AR, the rifle didn't get "quiet" until around 940fps. Pick a heavy bullet and keep working down in velocity until you reach your desired volume level.

The issue with the 150 is the case fill, as said above. To get subsonic velocities with a lightweight bullet will leave you with minimal case fill unless you have trailboss. But if you're going to use a pistol powder to try to make this work, you're asking for trouble. It's dang easy to double charge when you're playing that game, and the results really suck when that happens.
 
Your problem is you are comparing a semi-auto to a bolt gun a semi-auto is going to be louder shooting sub-sonic....nothing you can do about it unless you shoot single shot and make sure the action does not open up....
Powders you're going to need to work with what you can get some powders are quieter that others.....I really like TrailBoss but the case on a 300 BO is very small and using a 150 gr bullets there not enough space to get enough powder in the case to even get close to 1000 fps.....
A 308 Win. case is about the right size for TrailBoss....I load sub-sonic it a very good powder and the right size case.....
 

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