.223 subsonic loads with enough pressure to reliably function AR...

[C23]

Keep in mind that 36gr and 40gr are the common 22LR weights , same diameter, which fly at these velocities.

55gr with a short bearing surface will be safer to shoot through a suppressor , where it's legal, or a muzzle device.

The heavier bullets are great but they are extremely hard to stabilize. Many Americans have destroyed suppressors because of this.

Sure, you can get a 112gr to cycle quite easily, but we have confirmed evidence and data of keyholing, even with a 1:7 twist.

 

[jethunter]

Keep in mind that 36gr and 40gr are the common 22LR weights , same diameter, which fly at these velocities.

55gr with a short bearing surface will be safer to shoot through a suppressor , where it's legal, or a muzzle device.

The heavier bullets are great but they are extremely hard to stabilize. Many Americans have destroyed suppressors because of this.

Sure, you can get a 112gr to cycle quite easily, but we have confirmed evidence and data of keyholing, even with a 1:7 twist.

Good to know if and when we can start using suppressors. Which we can't now.

 

[C23]

Sir, with a 1:12 twist, I would advise a CMMG 22LR conversion kit and 40gr CCI.

 

[Ganderite]

I'm contemplating developing a subsonic .223 load using heavier bullet weight with smaller charge of fast powder to develop enough pressure to function action.

Has anyone else tried this?

Thanks,

Mark

You later said the rifle was 1:12 That is a real problem. Low velocity means low RPM and poor stability. This means heavy bullets won't work.

A 1:7 would be the rifle to shoot. can you borrow one of those?

I have made sub-sonic for a suppressed 308. I used 200 gr round nose bullets. 2400 was my powder choice. It was a bolt rifle.

 

[Meroh]

You later said the rifle was 1:12 That is a real problem. Low velocity means low RPM and poor stability. This means heavy bullets won't work.

A 1:7 would be the rifle to shoot. can you borrow one of those?

I have made sub-sonic for a suppressed 308. I used 200 gr round nose bullets. 2400 was my powder choice. It was a bolt rifle.

While I may not even move forward with this project; I'm an engineer, and I like a challenge; and the challenge is to make the rifle at hand function. While others may have done the ground work; they are few that are willing to share the info. I will be doing a lot of research to establish a starting point and when I'm reasonably certain that it could be done, then I would proceed. I need a baseline.

 

[zuke]

Keep in mind that 36gr and 40gr are the common 22LR weights , same diameter, which fly at these velocities.

55gr with a short bearing surface will be safer to shoot through a suppressor , where it's legal, or a muzzle device.

The heavier bullets are great but they are extremely hard to stabilize. Many Americans have destroyed suppressors because of this.

Sure, you can get a 112gr to cycle quite easily, but we have confirmed evidence and data of keyholing, even with a 1:7 twist.

Aguila S,S,S uses a 60gr boolit. a 22 short case with the OAL as standard 22 ammo. And the burnt powder has an "unpleasant" aroma.

 

[C23]

With a 1:12 twist , please refer to the Greenhill formula.

Stabilizing any projectile with a long bearing surface will be difficult at these velocities.

 

[Meroh]

Aguila S,S,S uses a 60gr boolit. a 22 short case with the OAL as standard 22 ammo. And the burnt powder has an "unpleasant" aroma.

I may be wrong as I have not tried these, but I believe that the "unpleasant aroma" is due to the fact that they get their power from a large dose of primer, and no powder.

 

[C23]

Please make sure to remove any muzzle device prior to your R&D.

You can destroy your flash hider/muzzle device with an unstable, tumbling, projectile.

People have a hard time even with a 1:7 twist, so you can imagine that with a 1:12 it will be a nice engineering challenge.

Keep me posted Sir.

 

[Andy]

My next project is to develop subsonic 223 loads with a 50 gr bullet and a wide range of burn rates, from Unique to US869.

I'm confident that none of these will cycle an AR-15, certainly not an unmodified one. I'm just curious about:

- subsonic loads in the 223;
- with a wide variety of powders;
- using a 50 gr bullet; that will
- stabilize in a common 1:9 twist.

With loads established, they can be tried in a 223 bolt gun, and for the adventurous, in an AR-15.

 

[zuke]

I may be wrong as I have not tried these, but I believe that the "unpleasant aroma" is due to the fact that they get their power from a large dose of primer, and no powder.

That could be so. I've never pulled 1 apart. They stabilize well in every Cooey and Savage I've tried them in.

 

[Andy]

My next project is to develop subsonic 223 loads with a 50 gr bullet and a wide range of burn rates, from Unique to US869.

I'm confident that none of these will cycle an AR-15, certainly not an unmodified one. I'm just curious about:

- subsonic loads in the 223;
- with a wide variety of powders;
- using a 50 gr bullet; that will
- stabilize in a common 1:9 twist.

With loads established, they can be tried in a 223 bolt gun, and for the adventurous, in an AR-15.

As I proceed with making up various loads to try (once it's warmer), a fairly extensive Web Search (which I would never describe as "research") has revealed a few things:

- there are practically no loads, aside from what Hodgdon provides, being shared, even from people who claim to have tried this; and
- a blind, unquestioned obedience to the "Rules for the Safe Operation of Subsonic Loads" (Author unknown).​

Here they are:

Rules for the Safe Operation of Subsonic Loads:

1. Drill Flash hole to 3.5mm (0.138", up from the typical 0.080") to allow all the primer flash to enter the case and ignite the powder completely;
2. Use Magnum Primers for maximum primer flash and better powder ignition;
3. Lube all bullets. Moly is good, animal fat is better;
4. Lubricate the bore regularly while shooting;
5. Never crimp bullets into cases. Never seat bullets "into the lands.";
6. Try NOT to use powder charges of less than 40% load density;
7. If load density is less than 40%, use tamping or fillers to keep the powder at the bottom of the case;
8. Make sure the bullet exits the bore after each shot;
9. Use only the fastest burning pistol powders - N310, N312, Bullseye, Clays, Titewad, HP38, Red Dot; and
10. Any sort of slow ignition or hangfire is a warning of imminent Secondary Explosive Effect (SEE).​

I have loaded countless subsonic rounds:

- with cast and jacketed bullets;
- with pistol and rifle cartridges;
- with fast and slow powders;
- in pistols and rifles;​

and I have typically not followed any of the "rules" (excepting #8, and #10 which is a warning).

Why start now?

Has anyone else questioned this?

 

[Ganderite]

Drilling out the flash hole will reduce ignition. The smaller the better.

Try both and compare ES and SD.

 

[Andy]

Drilling out the flash hole will reduce ignition. The smaller the better.

Yes, this is well known by Bench Rest competitors and the demand for small diameter flash holes is being met by such brass manufacturers as Lapua.

"Rule #2" (use of Magnum Primers) however can make sense.

I'll first try several loads with standard primer and flash hole, then choose promising loads and do a comparison with magnum primers along with drilled (to only 7/64" as it's a Small Rifle Primer) and not drilled flash holes to see what effect that might have.

 

[Cameron SS]

You are looking for low velocity and high pressure (to cycle the action). I think a heavy bullet is required. I would start with 80 and 75 gr bullets.

You'd be right at the edge for max OAL and still being able to stuff the rounds in the magazine.

While I may not even move forward with this project; I'm an engineer, and I like a challenge; and the challenge is to make the rifle at hand function. While others may have done the ground work; they are few that are willing to share the info. I will be doing a lot of research to establish a starting point and when I'm reasonably certain that it could be done, then I would proceed. I need a baseline.

Please make sure to remove any muzzle device prior to your R&D.

You can destroy your flash hider/muzzle device with an unstable, tumbling, projectile.

People have a hard time even with a 1:7 twist, so you can imagine that with a 1:12 it will be a nice engineering challenge.

Keep me posted Sir.

Bullets don't tumble in the barrel. Id suggest unless your muzzle device is more than 12" long, I don't think you'd have to worry about tumbling bullets damaging a muzzle device.

To the OP, Question for you, is your intent to make this ammo work with a standard un-modified AR, or will you permit modification of the gun in order to make this work?

IF you are unwilling to modify the gun, then I suspect the heaviest bullet you can use is going to be a given. I'm torn between predicting that a fast burning or a slow burning powder would be ideal.

Slow burning powder in a 16> " barrel will likely result in unburnt powder going out of the barrel with no contribution to cycling the gun. I suspect faster burning powder is going to generate the GASES that you need fast enough to drive the action before the bullet exits the barrel, but I'd be concerned about a relative small window of success before you start encountering excessive chamber pressures.

Definitely an interesting experiment to see if modifications to the ammunition alone can get you there.

If you are willing to modify the gun, then I suggest you consider any of the following modifications that will improve your chances of success.

1) Rechambering the gun in .300 blackout. Its basically what this round was invented for.
2) Installing a variable gas block to increase the amount of gas permitted through the system to drive the action.
3) Moving to a pistol length carbine system on as long a barrel as you would tolerate. This should probably be used in conjunction with a variable gas block.

 

[C23]

It is obvious that this would be a lot easier to accomplish with a heavier projectile.

However, if the rate of twist is not appropriate, the bullet would be unstable and wildly inaccurate and of little practical use.



If you have a very fast twist barrel, the Barnes 85gr Match burner would be a good candidate for testing. This is a little known bullet designed to feed in a magazine at 2.260" COAL. It has a similar geometry to the 77gr SMK. It does not get the credit it deserves.



Subsonic loads are easy to accomplish with Trail Boss, Titegroup and Bullseye. There is published data for this and it is perfect for a bolt action rifle. However, the lack of port pressure is inadequate to send enough gas and pressure down the gas tube to cycle the action.


I know from vast R&D that even a powder such as H4895, at subsonic velocity won't cycle the action unless the rifle is modified with a lighter bolt, enlarged gas port, light buffer and spring.



So the challenge is getting enough gas down the gas tube and having a stable projectile.

 

[C23]

Just like we learned in the .300 Blackout: Pistol length gas system is the way to go.