Help with AA#9 failure function

[redmo]

Well I experienced a weird problem. I have loaded AA#9 with Nosler 190 for subsonic load and have perfect function and very quite load in my 9” AR. But, when I tried the same load in my 16” AR, I could not get it to function even with adjustable gas block all the way open. It was as if it wasn’t getting enough gas to function. I had always assumed 16” would function easier than 9” and was surprised. A1680 subsonic load functions both fine. What am I missing?

[John A.]

I don't like to speculate on these types of problems without having it in my hands and some time with it.

But #9 typically burns out rather quickly and peaks, and doesn't specifically continue to increase in gas pressure due to the longer barrel.

Are you using the same lower? Buffer spring/buffer weight? Gas block?

Reason I asked, is any difference could be why one is working and the other isn't.

I even encountered a very odd anomaly with my gas block that I was using. My barrel had a .120" gas port, but when I took the gas block off, it was drilled about .079" (which is approximately what an M4 556 barrel would use).

So, that's why I don't like to get into a lot of "THIS IS WHAT'S WRONG WITH YOUR GUN" type of troubleshooting online. And that's not even starting to take into consideration the loads and barrel chamber and other things.

[dellet]

That will be a hard powder to get function and stay subsonic with that light of a bullet in that length barrel.

If it is carbine gas length it will be that much harder.

And as John said, build details and load details are a must before you could even hope for an answer.

[redmo]

Gotcha. Too many variables. I just was surprised as normally the 16” is easier to cycle than 9”. Both are pistol length. I do have JP piston buffer in 9” so may try changing that to see.