Subsonic and ARs

[RWBlue]

Is it easier to get heavy or lighter bullets to fly subsonic and make the AR-15 work?

My AR works fine with supersonic rounds, but I have yet to get it to function properly with subsonics.

Should I be working on 165gr bullet and then the 220-240s or should I try to get the 240gr to work and then play with the 165gr ers.

I have a pistol length gas system.

With the adjustable gas system, I assume I will get them all to function, but so far, no joy.

[RWBlue]

Thank you for the person who PMed me the powder recomendation and bullet.

[WhisperFan]

Originally Posted by RWBlue

Is it easier to get heavy or lighter bullets to fly subsonic and make the AR-15 work?

My AR works fine with supersonic rounds, but I have yet to get it to function properly with subsonics.

Should I be working on 165gr bullet and then the 220-240s or should I try to get the 240gr to work and then play with the 165gr ers.

I have a pistol length gas system.

With the adjustable gas system, I assume I will get them all to function, but so far, no joy.

You mentioned you have a pistol length gas tube. But what is your barrel length? And what is the diameter of the gas port?

I have an AR with a 10.5" barrel, a 7" gas tube (pistol length) and a gas port diameter of .110"
I shoot 220 SMK's with 8.5 grains of AA #9. The system fires, extracts and feeds really well.

[RWBlue]

That is a very good question. The barrel is 10.5 inches long and I am using a Gemtech HVT so that should help the issue. I don’t know the size of the gas port. The barrel is a Noveske semi-custom barrel and I am using an adjustable gas block. I assume if I get close to the right load, I can tweak it at the gas block. My fear is that the gas port is too small, but that remains to be seen.

Now, if I could just find a load for a powder that I have or find a powder that is recommended locally. I have on hand
2 Bullseye x
13 Red Dot x
14 Clays x
32 Green Dot x
44 Unique x
47 SR-7625 x
50 Power Pistol x
81 AA-7 x
83 Blue Dot x
91 2400 x
98 W-296 x
111 H-4198 x
123 AA-2015 x
132 IMR-4895 x
161 Varget x

[pug]

It should function with the W296 since you have that on hand. For subsonics the longer the dwell time in the barrel the better it functions so start with 240s and work your way back. Generally the gas valve needs to be run closer to being full open for subsonics.

[sniperx]

Originally Posted by RWBlue

Thank you for the person who PMed me the powder recomendation and bullet.

I did not mean for it to be that much of a secret

[RWBlue]

I am using my ear as the chronograph. Using w296, I go from subsonic to supersuper sonic. I don't think the port is large enough. Please see my post on the other forum about altering the gun, opening up the gas port.

[pug]

There are many things that determine what burning speed powder is most suitable for the particular application. Case capacity, bullet weight, barrel length and of course desired velocity are among the top. If you are not using 240 gr bullets then W296 would be a somewhat slow burning powder for the case capacity and the lighter bullets will go supersonic. 2400 is a somewhat faster burning powder and is suitable for lighter bullets . Opening up the gas port is the very last thing you will want to do and if your barrel is ported in the pistol position then I would look closely at everything else first. I assume you have at least 5 inchs of barrel in front the gas block since it is a 10.5".

[RWBlue]

With the 240gr SMK, I went up to 10.5gr win296. Although I am not using a chronograph, but my ears tell me that is it super sonic. I am beginning to think that this barrel is ported for supersonic ammo only.

I like the idea of trying 2400 with the 240gr bullets. According to my burn chart it should be very close to AA#9.

I will try 2400, but I don't think it will solve my issue.

BTW, I would love to hear what the MAX load is for 2400 and 240gr bullets.

[pug]

If it would not cycle correctly till you got to 10.5 grains of powder then yes you probably need to look elsewhere. There is the gas block adjustment itself as well as the alignment of barrel port to block and tightness of block. There is alignment of gas tube to carrier key as well as the condition of the key itself (cracked or loose). The position of the gas ring spaces should be checked as well as the fit of the rings in the carrier. All sorts of tests for that but one is to extend the bolt and then set the entire bolt/carrier boltface down on a table and the carrier should not drop under its own weight. The carrier assembly should slide smoothly in the receiver with no sign of binding. The power of supersonic rounds mask these things but with low power subsonic rounds they can show up. And of course there is the port size and its position on the barrel. A set of pin gauges or a set of number size drills will give you an idea of the port size.