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300BLK: 150g sub loads. Is this possible?


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I’m just trying to make cheap and fun sub loads for my suppresses 300BLK.

I have a 8” barrel 300BLK and right now a shop by me sells a 215g Polly coated bullet for $50 per 250 bullets. Figured if I can get these 150g bullets to a subsonic velocity, it will be cheaper. I don’t know if this is possible but I’m sure someone has tried it.

I’m using CFE black

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I think you’d have cycling issues. Out of a bolt gun sure you could. It wouldn’t be accurate or have any kind of range but you can do just about anything. 
 

since you’re talking subs I’m guessing you have a can.  The thought of the round tumbling would be enough to spook me away from it. 

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I tried a number of different subsonic 150 loads and couldn't get them to cycle in an AR.  Tried lightweight bolt carrier, lightest buffer I could find, and pretty much everything I could think of.

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On 2/1/2021 at 3:19 AM, Atlasguy321 said:

I’m just trying to make cheap and fun sub loads for my suppresses 300BLK.

 

Yes it is and many are doing it. However, what is your definition of a "sub load?"

 

Normally it's solely based on velocity and there are factory sub loads.

 

As far as cycling goes, considering PCCs shoot some very "sub loads" (yes they are bow back, except for the CMG which has a true locking bolt) and have no problems cycling I'm not sure why some are having difficulties.

 

Change the buffer spring and weight to tune the bolt cycling, polish parts of the bolt, use a good grease on the bolt, make sure the bolt group functions smoothly (as in the rotation for lock up and unlock), the gas tube needs to be clean, and all the ammo has to fit properly in the chamber.

 

A lot of people shoot 300 BLK out sub sonic.

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6 minutes ago, HesedTech said:

 

Yes it is and many are doing it. However, what is your definition of a "sub load?"

 

Normally it's solely based on velocity and there are factory sub loads.

 

As far as cycling goes, considering PCCs shoot some very "sub loads" (yes they are bow back, except for the CMG which has a true locking bolt) and have no problems cycling I'm not sure why some are having difficulties.

 

Change the buffer spring and weight to tune the bolt cycling, polish parts of the bolt, use a good grease on the bolt, make sure the bolt group functions smoothly (as in the rotation for lock up and unlock), the gas tube needs to be clean, and all the ammo has to fit properly in the chamber.

 

A lot of people shoot 300 BLK out sub sonic.

 

Not sure what your point is.  The problem with 150g subs is a lack of pressure.  And yes, subs will cycle an AR just fine if you're using a heavier bullet and the gun is set up correctly.  But the OP inquired about 150g subs, which is a different story.  I'm not aware of any subsonic load with a 150g bullet that will cycle an AR.  If you have something that works, please share it.  The fact that subs work fine in a blow back pcc is completely irrelevant.

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2 hours ago, ltdmstr said:

 

Not sure what your point is.  The problem with 150g subs is a lack of pressure.  And yes, subs will cycle an AR just fine if you're using a heavier bullet and the gun is set up correctly.  But the OP inquired about 150g subs, which is a different story.  I'm not aware of any subsonic load with a 150g bullet that will cycle an AR.  If you have something that works, please share it.  The fact that subs work fine in a blow back pcc is completely irrelevant.

 

My point is it takes experimentation and there are people actually doing this. The fact you may have had some issues is not a blanket statement no one should attempt or use 150 grain sub loads.

 

As far the cycling goes, it's all about tuning the gun to match what I'm shooting. 

 

The real answer is, it is easier to develop loads for heavier bullet. 

 

Here's a load from another site developed and working in an AR platform (8" Wilson Combat barrel, standard gas port size and gas block, pistol length gas system, 1-7" twist):https://www.sniperforums.com/threads/150gr-sub-sonic-loads-for-300-blackout.86320/

 

"Update. I ended up using Lil' Gun powder, for my sub loads with the hornady 150gr fmj/bt. I managed to get MOA accuracy, and consistent speeds of 1,050fps with 8.5gr., Winchester brass, Remington 7½ primers,and base to give length of 1.500". 

 

BTW, Yes most use 190 gr (which I use with a 16" standard barrel) or higher for sub loads. Just don't throw a wet blanket on the OP's desire to use 150 gr bullets, just ladder the load down to a subsonic level with a Chrono.

 

Edited by HesedTech
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That post doesn't say anything about cycling the gun.  I've done plenty of subs with 150s and single shot they work just fine.  But none generated enough gas to cycle the gun and keep it running.  I've tried skeletonized bolt carriers, the lightest buffer/spring combination possible (basically hollow plastic ends and a Tacom super lw spring), and pretty much everything else, and couldn't make enough gas to cycle.  If I can find some Lil Gun I'll try his load of 8.5g.

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Okay I loaded two sets of subsonic rounds with two different Bullets and powders. 
Shot out of PSA 16” AR platform all stock PSA parts except for lower, which was a personal build.
 

.308 FMJ 148 grain BT (I use for my M1) Shooters World Black 12.0 grains 2.19” 1050 FPS, 25 yards (indoor test) 1” accuracy. Ten out of ten cycled and ran gun fine. I used a Magpul magazine.

 

.309 158 grain FN coated (SNS bullet used for 30-30 Winchester 94) Trail Boss powder 6 grains (max filled BTW). The powder load was amount recommended for 300 Black Out, but truthfully this is a terrible combo. The powder did not fully ignite and left a lot of crud in the barrel and chamber. The bullet did fire down range without tumbling but did not cycle the gun. After three tries abandoned the test. I’ll pull the bullets and reload the brass with Shooters World.
 

I believe the coated Bullets would work with the Shooters World or 300 CFE without issues. 
 

The point is this 150 grain Bullets loaded subsonic shoot fine in a standard 16” barreled rifle. The only question is using a shorter gas tube with a sub 9” barrel may be different. 

 

Hope this makes sense and helps. 
 

Let me add this, I would consider dropping as low as 10.5 grains of Shooters World, which should give about 900 FPS velocity with the 148 grain bullet. 
 

What’s fun about 300 bo is the gun is far quieter, unsupressed, than those shooting 9mm pistol. 

Edited by HesedTech
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