8.5” 300 Blackout 50/100 Yards — Potential.

JasonMPD

Here’s my yearly post—haha. 

I recently put togethet a 8.5” 300 Blackout SBR to try out as a possible “low signature” hunting gun. It’s suppressed with a Crux Nemesis 30cal/338cal suppressor (bored for 338, backwards compatible effectively to 30cal, smaller is less effective due to blow-by). 

Since the SBR parts were sourced from varied places, I opted for an adjustable gas block to try and author in some reliability since I did not select nor drill/ream my own gas port.  The gun will be suppressed one hundred percent of the time so increased back pressure will aid in cycling reliability.  Being a little over gassed helps 300 B/O anyhow. 

Atop the rig is a Vortex PST (gen 1) 1-4x, second plane reticle, with their TMR reticle. It’s subtended 6 MIL in all 4 directions and has an illuminated center portion for CQC at 1x. 

Many 300 B/O rifles are reliable but not so accurate. Not in the context of supersonic calibers that is. The subsonic game is a different thing. 100 yards for subsonic is like 600-800 yards for supersonic projectiles in a manner of speaking. It’s for close work and heavy bullets are name of the game for effective wounding. 

I randomly grabbed some Hornady Black 208gr AMax subsonic.  My Magnetospeed measured them reluctantly at 981 FPS, average. Slow projectiles give Magnetospeed sensors a tantrum and they had to have their sensitivity set to “high”.  

I was testing out a Maxim Defense PDW style stock and I won’t be using it on this rig after all. Cheek weld is dicey and it’s design doesn’t fit the mission of this SBR. It’s cool kit, but for another purpose perhaps. 

I had similar grouping at 50 and 100 yards. Typical? Actual? Weird?  I’m not sure. The stock gave me very poor consistency in the shoulder pocket and offered little cheek weld. But if it never does worse than it did today I’m all for it. It’s acceptable nevertheless. 

I’m not sure when I’ll get to plug a few in a critter or two, but I’ll report back when I do. Coyote first. We’ll see what a subsonic AMax does. 

Cheers. 

CHIRO1989

Looks good, fiddling with different ammo obviously makes a difference, keep fiddling. Have you shot it with out the supressor, how is the muzzle blast?

Diver43

Hey Jason, good to see you here.
Kool gun

JasonMPD

CHIRO1989 said:

Looks good, fiddling with different ammo obviously makes a difference, keep fiddling. Have you shot it with out the supressor, how is the muzzle blast?

The silencer adapter is a brake. When I get my hands on a flash hider version I’ll swap it. 

Supersonic...  The muzzle report is something between ouch and Jesus, Mary and Joseph.  The brake also expelled any unburned powers sideways at hyper speed. Ouchy on the forearms.  That’s the nature of a 8.5” blaster though.  Braked 10.3” 5.56 guns will do similar, but louder. 

Subsonic...  The muzzle report is no issue. It’s not absent by any means, but ignorable. Either way the flash hider will be preferable. 

zorba

Diver43 said:

Hey Jason, good to see you here.
Kool gun

Yea, that!

Don't be a stranger!

knitepoet

Which gas block did you go with?
Ive been extremely happy with the Superlative Arms "blow-by" blocks I have on my suppressed 223 and soon to be suppressed 16" 300BO
I've got a stripped lower I am seriously considering registering and getting me an 8.5" BO upper for it, to go with the 10.5" 223 upper I currently have on my pistol lower

knitepoet

FYI, my BO sbr (if/when built) will be set up as a PDF for 110gr V'maxs, or MAYBE 125 Sierra TMKs

knitepoet

FYI, the 208 Amax will either pencil though, or tumble, depending on how large the critter you hit is, and what you hit, bone or meat

JasonMPD

knitepoet said:

Which gas block did you go with?
Ive been extremely happy with the Superlative Arms "blow-by" blocks I have on my suppressed 223 and soon to be suppressed 16" 300BO
I've got a stripped lower I am seriously considering registering and getting me an 8.5" BO upper for it, to go with the 10.5" 223 upper I currently have on my pistol lower

The gas block is an SLR Rifleworks piece. Not blow by like Superlative Arms, but working well. 

The supers I shot were 110 VMax. 8.5” got them to 2100 FPS. About 2-3 MOA grouping. 

knitepoet

I have the one on my 20" suppressed 223 opened into blow-by mode to reduce the crap in the can. (25.0gr powder charge)
Until I get my stamp for my 30 cal can, I have the one on the BO in restrictive mode for the slight velocity boost.
With the lower charge (18.5-20.0gr) weight in the BO, I am considering setting the one I'll be putting on my bo pistol upper (When I get it) in restrictive mode as well.

JasonMPD

knitepoet said:

I have the one on my 20" suppressed 223 opened into blow-by mode to reduce the crap in the can. (25.0gr powder charge)
Until I get my stamp for my 30 cal can, I have the one on the BO in restrictive mode for the slight velocity boost.
With the lower charge (18.5-20.0gr) weight in the BO, I am considering setting the one I'll be putting on my bo pistol upper (When I get it) in restrictive mode as well.

To each, their own; but, I run my ARs suppressed and let them get dirty AF. They run. Keep them lubricated with gun oil (not grease) and stoppages are rare. Even the 300 BO guns full of soot and powder particles. 

I will say though run supersonics through your suppressors after a subsonic range session to clean them out though. 

CHIRO1989

JasonMPD said:

CHIRO1989 said:

Looks good, fiddling with different ammo obviously makes a difference, keep fiddling. Have you shot it with out the supressor, how is the muzzle blast?

The silencer adapter is a brake. When I get my hands on a flash hider version I’ll swap it. 

Supersonic...  The muzzle report is something between ouch and Jesus, Mary and Joseph.  The brake also expelled any unburned powers sideways at hyper speed. Ouchy on the forearms.  That’s the nature of a 8.5” blaster though.  Braked 10.3” 5.56 guns will do similar, but louder. 

Subsonic...  The muzzle report is no issue. It’s not absent by any means, but ignorable. Either way the flash hider will be preferable. 

Thanks, CDNN has a Levang style compensator for a reasonable price, I look at the bird cage compensators on the PSA uppers and was thinking loud

JasonMPD

Compensators are sometimes overrated additions. In 5.56 and 300 BO rifles they aren’t very necessary. Flash hiders do more, practically, for small arms calibers for me than brakes/compensators.

CHIRO1989

I like the Levang on my AR pistol in 5.56/.223, the report goes away from my face and ears and the gasses go away from my fingers, I was curious if the .300 BO was even more obnoxious that close to the face

JasonMPD

CHIRO1989 said:

I like the Levang on my AR pistol in 5.56/.223, the report goes away from my face and ears and the gasses go away from my fingers, I was curious if the .300 BO was even more obnoxious that close to the face

It’s just as obnoxious if not somewhat more with full power ammo.