Subsonic Ammo

[Gadsden]

I have a couple questions on the subject

1) I have some subsonic ammo for my AR, but the rifle won't cycle when I'm shooting them. Any idea what the problem is and how I can fix it?

2) Where can I find the information on how to hand load subsonic ammo, specifically for 223 and 308?

 

[adamsredlines]

Subsonic ammo has less pressure and thus less gas to run the gas system on an AR that is not set up for it. There are many ways to fix it such as gas Port size, adjustable gas block, buffer weights, buffer springs etc.

The fun if you are trying to run both supersonic and subsonic through the same gun is finding a happy medium that will run both without being extremely overgassed when running supers to the extent of beating up your gun.

 

[adamsredlines]

I am curious though, are your guns set up with a twist rate that will run heavier bullets that are generally used for subsonic? I think especially for 308 I assume that you're going to use something in the 200 to 220 grain range which would potentially need a different twist rate in a rifle that was set up for mil-spec 147 grain type stuff.

Unsolicited opinion I think you would be better off getting a 300 Blackout since it was pretty much designed to run subsonic. I never quite understood trying to make 308 subsonic. It seems like a more difficult and expensive way of getting the exact same end result as 300 blackout.

 

[Gadsden]

Subsonic ammo has less pressure and thus less gas to run the gas system on an AR that is not set up for it. There are many ways to fix it such as gas Port size, adjustable gas block, buffer weights, buffer springs etc.

The fun if you are trying to run both supersonic and subsonic through the same gun is finding a happy medium that will run both without being extremely overgassed when running supers to the extent of beating up your gun.

I forgot to mention my AR is direct impingement if that matters.

 

[adamsredlines]

The vast majority of them are

 

[Gadsden]

I am curious though, are your guns set up with a twist rate that will run heavier bullets that are generally used for subsonic? I think especially for 308 I assume that you're going to use something in the 200 to 220 grain range which would potentially need a different twist rate in a rifle that was set up for mil-spec 147 grain type stuff.

Unsolicited opinion I think you would be better off getting a 300 Blackout since it was pretty much designed to run subsonic. I never quite understood trying to make 308 subsonic. It seems like a more difficult and expensive way of getting the exact same end result as 300 blackout.

As it stands right now I have to make do with the guns I have otherwise I'd gladly look into a 300 Blackout.

 

[Profreedomokie]

I have a 300 Whisper AR (the 300 Bk Out's daddy) I built years ago. Location of the gas port plays into it also. I run an empty buffer weight with a 9mm recoil spring. I shoot .308 subsonics in a bolt gun only. If you're going to shoot heavy .30 cal bullets slow, you need a 1 in 8 twist. I have a Rem.700 PLT that is set up to shoot subsonic 167 gr. bullets. It would group around 1.5" at 100 yds.

 

[Gadsden]

The vast majority of them are

Okay, I guess I got the terminology confused. My rifle operates with a piston, not gas.

 

[adamsredlines]

For educational purposes they both run off of gas but how that gas is used is different.

Direct impingement is the vast majority of ARs and gas piston is used on some but they still utilize gas just in different ways to move the bolt carrier.

Laying out your exact setup would be greatly beneficial in helping with suggestions. I honestly do not know much about the gas piston systems on ARs but if I had to guess there are definitely differences between them and that information will help someone who is more familiar with that exact system and helping you diagnose your issue.

 

[Gadsden]

I have a 300 Whisper AR (the 300 Bk Out's daddy) I built years ago. Location of the gas port plays into it also. I run an empty buffer weight with a 9mm recoil spring. I shoot .308 subsonics in a bolt gun only. If you're going to shoot heavy .30 cal bullets slow, you need a 1 in 8 twist. I have a Rem.700 PLT that is set up to shoot subsonic 167 gr. bullets. It would group around 1.5" at 100 yds.

Okay my 308 is a bolt gun, but it's a 1 in 11 twist rate. My AR on the other hand has a 1 in 7 twist and is piston operated. So if I understand you I may need a different recoil spring so it will cycle correctly?