Subsonic .308 for suppressed rifles

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11 years 1 week ago #30491 by txlongshotb4
Replied by txlongshotb4 on topic Subsonic .308 for suppressed rifles
OK...Hijacked the wife's laptop for a little while-decided to spend the time with you guys.

I've yet to find any subsonic .308 that will cycle in a semi auto gun. I'm not sure an adjustable gas block would do the trick. The purpose of an adjustable gas block is to regulate the back pressure for supersonic loads with a suppressor, because the suppressor traps all of that gas and directs more pressure into the impengment system-so the adjustable gas block was created to lessen the gas pressure via "turning down" the valve much like turning your kitchen faucet down to a trickle. Subsonic loads do not create enough gas pressure to cycle the bolt by their own nature, and opening up the gas port is not going to fix that-the bullet is the powerhouse of the whole operating system-it will either generate enough force to cycle or it wont, and a subsonic .308 simply cannot generate enough force to do so unless more powder is added and velocities break the sound barrier.

I've seen one exeption to that rule, but it was a weapon system that was specifically designed to do so. It was an AR gun that had a custom 14.5 inch barrel that was gas ported at 9 inches and it had a custom built reduced tension buffer spring as well as a titanium bolt carrier group to reduce the resistance. It cycled subsonic ammo like a champ, but only when suppressed, and shooting supersonic loads through it would destroy it within less than a 30 round mag.

There is a company here in Texas called Engle Ballistic Research. They sell subsonic ammo, and if memory serves me correctly they have some that they claim will cycle-not sure if it's 5.56 or 7.62...I just know it's pricey.

Here's the thing-depending on how your rifle is set up, you might have anywhere from 2 to 8 or so inches of rifled bore out there on the muzzle end of your gun past the gas port.When you fire a round, you have absolutely positive compression of the gasses up until the back end of your bullet passes that port. Depending on how much pressure bleed off you have set on an adjustable gas block, you are losing compression every single millimeter of bore the bullet travels after that point. If you go changing the setting on your gas block, you are changing that comression, which changes muzzle velocity-even ever so slightly-and then you are effecting accuracy. I say leave it be...you are not going to get subsonic round to cycle by messing with it anyhow, and even if you could you would have to change it back to shoot supersonics which would be a real pain in the butt. There is a plus side to not having a subsonic round cycle anyhow- the noise of the bolt cycle never happens. Just treat it like a bolt action, manually cycle the next one, and keep the accuracy.
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11 years 1 week ago #30551 by 13fcolt
Replied by 13fcolt on topic Subsonic .308 for suppressed rifles
I go back and forth on the subsonic thing. About the time I get myself talked into it, I talk myself out of it in favor of building a .300blk upper and go that route.

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11 years 1 week ago #30562 by mlotziii
Replied by mlotziii on topic Subsonic .308 for suppressed rifles
.300 blk uppers are great but you're talking about an AR-15 upper.

On an AR-10 platform just build another .338 whisper which you can get 20% more energy from. With a .338 whisper you can push a 300 grain bullet vs the typical 220 gr .300 Blackout round.

You can get up to 40% more energy from the 300 gr bullet for more knockdown power.
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11 years 1 week ago #30567 by jtallen83
Replied by jtallen83 on topic Subsonic .308 for suppressed rifles
Where would one find a .338 Whisper upper?

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11 years 1 week ago #30577 by mlotziii
Replied by mlotziii on topic Subsonic .308 for suppressed rifles
The first place that jumps to mind is sskindustries.com/tactical

About half way down the page is an AR-10T that is suppressed in .338 whisper.

I've been drooling over that gun for about 10 years now.
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11 years 1 week ago #30587 by Sharkey
Replied by Sharkey on topic Subsonic .308 for suppressed rifles
Wow M. That does give some food for thought now doesn't it... :drool:

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11 years 1 week ago - 11 years 1 week ago #30591 by jtallen83
Replied by jtallen83 on topic Subsonic .308 for suppressed rifles
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.302,.338,.375, and .416!
A .416 Whisper! talk about sending a silent but deadly package downrange, I want one :usa:
Last edit: 11 years 1 week ago by jtallen83.

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11 years 1 week ago #30596 by SOC
Replied by SOC on topic Subsonic .308 for suppressed rifles
You really need a dedicated upper for subsonic shooting above 22LR. You just need a lot more twist for the heavy for caliber slow bullets.

If I was going to go subsonic I'd get an new upper for my AR-10 TU.

There is a .510 caliber (Uses true 50 BMG bullets) wildcat of the 300 RSAUM round designed to fit AR-10 mags.

I already cast lead. I think a custom 800gn hollow point flat base bullet would be pretty wicked at sub sonic speed from a 16" barrel AR-10.

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11 years 1 week ago #30624 by jtallen83
Replied by jtallen83 on topic Subsonic .308 for suppressed rifles

SOC wrote: You really need a dedicated upper for subsonic shooting above 22LR. You just need a lot more twist for the heavy for caliber slow bullets.

If I was going to go subsonic I'd get an new upper for my AR-10 TU.

There is a .510 caliber (Uses true 50 BMG bullets) wildcat of the 300 RSAUM round designed to fit AR-10 mags.

I already cast lead. I think a custom 800gn hollow point flat base bullet would be pretty wicked at sub sonic speed from a 16" barrel AR-10.


Ant more details? If I'm gonna spend the money to throw big lead I want to throw as much as I can!

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11 years 6 days ago #30672 by SOC
Replied by SOC on topic Subsonic .308 for suppressed rifles
www.teppojutsu.com/500_Phantom.htm
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