Question for our M4/AR experts

**KeithPA** · November 10th, 2007, 02:13 PM

So I've been searching to find a way to get an AR to cycle with subsonic rounds. Unfortunately I was thinking about the problem completely wrong, and simply searching for ammo.

Well after talking to two friends, both who used to be in ranger battalion and mentioned that they had M4s that cycled with subsonics. They said that they had custom made gas tubes that had a narrower (word?) gas port, so it boosted the pressure. Obviously you could only use subsonics without having to switch out the gas tube to the original.

Anyone know where to find this?

Or, does anyone know what the gas pressure that would go through the tube be? Or what pressure is required to cycle the bolt? I could probably calculate and model the part, at a huge cost is no one makes one.

Thanks

**fultonCoShooter** · November 10th, 2007, 04:35 PM

Whats it doing? short stroking, not cycling at all alittle more info would help

**KeithPA** · November 10th, 2007, 04:43 PM

What I'm saying is there isn't enough pressure to move the bolt carrier back.

It won't cycle at all. Thats just how subsonic ammo is.

Same thing with my P22 if I use subsonic rifle ammo (since all .22 ammo is pretty much subsonic outta a pistol). Cept for an AR it relys on a gas tube. So making the inner diameter smaller would increase the pressure, allowing for a subsonic .223 (that has about 1/3 the pressure) cycle the bolt carrier.

Unless someone knows of subsonic .223 that will cycle, I've never heard of such ammo.

**fultonCoShooter** · November 10th, 2007, 05:25 PM

HMM i have no idea i dont own a can

although the thought of subsonic ammo in a AR sort of alarms me.

with a can your AR should sound like a unsuppressed 22 with normal ammo.

what alarms me with subsonic ammo is there prolly isnt enough velocity to make the bullet Frag.

a subsonic round with a heavier weight bullet would increase the pressure but we are talking prolly 75gr and up

there is a rumor that Engle Ballistic Research is designing a subsonic round that will cycle but i can not find any info about it, although if u want maximum quietness the bolt not cycling would be what you want anyways

you could always get a 300 whisper upper

sorry i cant be more help oh and i am not a expert with ARs but i know alittle bit

**TonyF** · November 11th, 2007, 01:37 AM

Yes the gas ports are often tweaked both for ammo and (short) barrel's. I don't know if it's possible to calculate on paper what you're hoping to discover.

Where are you finding subsonic .223 ammo?

**Mtdew** · November 11th, 2007, 02:45 AM

Originally Posted by DeltaII5

So I've been searching to find a way to get an AR to cycle with subsonic rounds. Unfortunately I was thinking about the problem completely wrong, and simply searching for ammo.

Well after talking to two friends, both who used to be in ranger battalion and mentioned that they had M4s that cycled with subsonics. They said that they had custom made gas tubes that had a narrower (word?) gas port, so it boosted the pressure. Obviously you could only use subsonics without having to switch out the gas tube to the original.

Anyone know where to find this?

Or, does anyone know what the gas pressure that would go through the tube be? Or what pressure is required to cycle the bolt? I could probably calculate and model the part, at a huge cost is no one makes one.

Thanks

The quick answer is you cant.

Here is the long answer
in order for it to cycle in a standard AR you need either 100grn bullets (ES is using powerded tungsten & they are not cheap) https://www.extremeshockusa.com/cgis...d=2651062.1452

or a gas port drilled MUCH closer. If i were to guess a pistol length gas system MAY work on a carbine length barrel.

and nothing aganst your friends but a smaller gas port/tube does not increase pressure, it will only reduce volume. The only way to increase pressure is to move the port closer the the chamber.

personally I think sub 223 is a waste since you effectivly reduce it to a 22RF