Help with 300 black out

[cheek9075]

Ok I am trying to get a 300 blackout to shoot subsonic rounds. The upper is a surplus ammo complete upper. The lower is a Anderson, with mil spec lower kit, jard trigger, and a 6 postion stock that came with the lower kit. Specs on the upper are listed

• Caliber: 300 Blackout
• Bolt & Carrier Group: SAA Phosphate BCG
• Upper Receiver: SAA
• Upper Receiver Material: Forged 7075T6 A3 Flattop with T-Markings, American Flag, & SAA Logo
• Gas Block: Low-Profile Gas Block
• Gas system: Pistol-Length
• Front Sight: None
• Barrel Length: 16"
• Barrel Material: 416 Stainless Steel
• Barrel Profile: HBAR (Heavy Barrel) Profile .750" Diameter at the Gas Block
• Twist Rate: 1:8.5 Twist
• Thread Pitch: 5/8x24
• Flash Hider: A2 Birdcage Flash Hider
• Handguard: Yankee Hill Free Floated Specter Diamond Quad Rail
• Additional Info: M4 Style Feed Ramps, Complete with Charging Handle

I am using cci small rifle primmer, h4198 11.2 grs, and palmetto projectiles 203gr polymer coated lead bullets, at 1.950 to tip of bullet. The load data is palmetto.

Rounds fire, but will not cycle and load the next round. They are ejecting about 1/2 the time, maybe a little more than 1/2. Looks like I'm up around 1050 fps, so the load seems to be on where it is at. What do I need to change on the rifle ti make it cycle? Buffer spring? Gas block?

I

 

[SheepDog]

It sounds like you need to go to a heavier bullet. If you raise the powder level it will be too fast and going to a faster powder may not give you an increase in pressure at the tube.
I just looked and found that Hodgdon has a load for a 208 grain Hornady A-Max listing 9.2 grains of H110 for higher pressures and lower velocity than your load. You might try that.

 

[Auto-X Fil]

What buffer weight? I would try a lighter buffer or ream the gas port a little bigger. An adjustable gas block won't help any.

Any idea what the current gas port size is?

 

[Cool Tool]

Well you chose the wrong twist my opinion that is your problem.

 

[people]

What buffer weight? I would try a lighter buffer or ream the gas port a little bigger. An adjustable gas block won't help any.

Any idea what the current gas port size is?

Buffer weight is where I would look first. Yes go lighter.

 

[people]

Well you chose the wrong twist my opinion that is your problem.

That would not cause ftf and fte.

 

[Cool Tool]

That would not cause ftf and fte.

do you have time to spell out what you said I am not much on computer jargin

 

[cheek9075]

Looks like 3.6oz buffer. I ordered a lighter buffer, and buffer spring from Nemo for a 300 blackout. I will try that and then open up gas if that doesn't work.


Ftf- failure to fire/function
Fte- failure to eject.

 

[rifleman700]

Ok I am trying to get a 300 blackout to shoot subsonic rounds. The upper is a surplus ammo complete upper. The lower is a Anderson, with mil spec lower kit, jard trigger, and a 6 postion stock that came with the lower kit. Specs on the upper are listed

• Caliber: 300 Blackout
• Bolt & Carrier Group: SAA Phosphate BCG
• Upper Receiver: SAA
• Upper Receiver Material: Forged 7075T6 A3 Flattop with T-Markings, American Flag, & SAA Logo
• Gas Block: Low-Profile Gas Block
• Gas system: Pistol-Length
• Front Sight: None
• Barrel Length: 16"
• Barrel Material: 416 Stainless Steel
• Barrel Profile: HBAR (Heavy Barrel) Profile .750" Diameter at the Gas Block
• Twist Rate: 1:8.5 Twist
• Thread Pitch: 5/8x24
• Flash Hider: A2 Birdcage Flash Hider
• Handguard: Yankee Hill Free Floated Specter Diamond Quad Rail
• Additional Info: M4 Style Feed Ramps, Complete with Charging Handle

I am using cci small rifle primmer, h4198 11.2 grs, and palmetto projectiles 203gr polymer coated lead bullets, at 1.950 to tip of bullet. The load data is palmetto.

Rounds fire, but will not cycle and load the next round. They are ejecting about 1/2 the time, maybe a little more than 1/2. Looks like I'm up around 1050 fps, so the load seems to be on where it is at. What do I need to change on the rifle ti make it cycle? Buffer spring? Gas block?

I

Without being there and seeing the issue I would have to say your sub rounds do not create enough pressure to cycle the bolt. Increase your charge and re-test. Adjustable gas block may also help. The best fix would be to just run a can. Subs run best with a can.

 

[Cool Tool]

Looks like 3.6oz buffer. I ordered a lighter buffer, and buffer spring from Nemo for a 300 blackout. I will try that and then open up gas if that doesn't work.


Ftf- failure to fire/function
Fte- failure to eject.

Thanks for update now iunderstand but trust me he has the wrong twist for shooting that bullet weight subsonic.

 

[Sniper338]

Its your buffer spring. I need to change the one in mine too, just havent done it..

 

[cheek9075]

I may have the wrong twist. This is my fist rodeo with a 300 blackout. For the most part I learn for my mistakes, even if it takes me 3 or 4 times....
When I get it cycling like it should, I will find out how it shoots. If the twist is a problem I will fix it then... This is a leaning curve for me. I researched a little, a 1:8 will stabilize 220gr and up. A 1:10 is good for 170gr to 220gr. So maybe the 1:8.5 will work. We will see.

Thanks for all the replies. I figured I need a lighter spring and buffer. But thought an adjustable gas block would help. But it is limited to the hole size.

 

[people]

Thanks for update now iunderstand but trust me he has the wrong twist for shooting that bullet weight subsonic.

Yes he does but it should still function. With that being said you never know until you shoot them. It might be a little faster than stated or by some fluke it might just shoot well enough.

 

[cheek9075]

Without being there and seeing the issue I would have to say your sub rounds do not create enough pressure to cycle the bolt. Increase your charge and re-test. Adjustable gas block may also help. The best fix would be to just run a can. Subs run best with a can.

Have a can on the way if ATF ever gets the tax stamp back......

 

[Hoser]

A bigger gas port will help.

 

[germanlongbow]

Adjustable block will help. One rifle standard recoil spring, second rifle JPS silent spring. Both will cycle reliably once adj gas block is tweaked. I shoot a 16" and a 8.5" suppressed. 1x8 twist better option with heavey 200+ grain bullets. Better luck with 1680 Accurate powder, start at 9.0 grains and work up with chrono. Bolt rifle also 1x8 twist 16". Shoots same load 9.8gr Accurate 1680. Very quiet.

 

[yotehater]

If you do ream out the gas port an adjustable block is going to be necessary unless you get lucky. I have had good luck with the lighter buffer weight and no can. Good advice on changing powder to increase pressure with same bullet weight. 1680 is a good one.

 

[bradleya479]

Real simple fix have a qualified Smith enlarge gas port an run a adjustable gas block and you can go from subsonic to supersonic with a simple adjustment!

 

[geraldgee]

I believe that Accurate 1680 or IMR 4227 are the preferred powders for subsonic blackout. I would certainly try a different powder before making any hardware changes.

http://www.300blktalk.com/ is a site devoted to the 300 Bkackout. Great advice available there.

Good luck

Gerald

 

[Rick in Oregon]

You may want to check out the new CFE BLK powder for subsonic loads in the 300 AAC Blackout, as according to Hodgdon, it is optimum for this caliber and subsonic loads. It's new, so may take a while to show up on dealers shelves. The new 2017 Hodgdon Annual Reloading Manual has a feature article on this new powder.

Also ideal for the 221FB and other small varmint rifle calibers.