I have a Sig 553R. I have Brown Bear 196gr subsonic ammo. It cycles reliably, even on reduced gas apertures.

I got some Hornady 255gr SubX. It won't cycle even on the largest gas setting. I guess it's intended for bolt actions.

Apparently PPU makes some 182gr subs. I'd like to think they'd work, as they're potentially closer in composition to the Brown Bears. The Brown Bears are unfortunately unobtainium now.

Anyone else have any experience with 7.62x39 subs in a semi-auto?

Why don't more companies make more different options? The Brown Bear is proof that it's viable.

I should make it clear that I am not trying to make a 7.62x39 rifle do what a .300BLK does better. I have the x39 rifle to primarily shoot regular ammo. I use a suppressor, and the subsonic option is a cool one to have. It's not like 5.56, where the subs are never going to cycle it and I may as well be shooting a 22LR, so I don't think it's unreasonable to be a bit annoyed that there aren't more subsonic options out there.

This message has been edited. Last edited by: KSGM,

I have only used the Hornady. It cycles in my Bren2. But that's not many rounds, I was originally going to try to set the Bren up for volume shooting suppressed but its not something I decided to continue to make work.

I was planning to pick up some Hornady 255 to go in my Galil Ace pistol. That thing is so overgassed, if it can’t run it, I’ll be surprised.

Based on hrcjon's reply, I think I am going to mod another gas valve with an over-sized port, in an effort to make the Hornadys run.

If funds allow, I'll also try to pick up some of the PPU.

That made me think of a related issue. As you know I'm a SCAR fan and those have factory replacable gas jets in a huge range of sizes. The internet is full of advise on what to use for specific setups but like all internet things opinions vary. But its so trivial to change a jet size you can treat any info as optional. Do there exist communities for other platforms that discuss jet sizes where you have to actually drill holes. For example on KSGM Sig is there a knowledge base that says a good starting point is .187 for a 10" barrel and this ammo, or are you on your own to figure it all out.

I had no idea that Brown Bear made subsonic ammo.

quote:

or are you on your own to figure it all out

I think so.

This being a more unique rifle/ammo/silencer combination, I'd guess there's not a lot of talk out there. I am not a member of any other forums, so I'd be at the mercy of existing conversations found with google. A search doesn't yield anything useful.

Since I may actually do this on my Bren what's your thinking on a strategy (since it seems you have already done it) to get to the size you need but not over the size you need without wasting too much ammo/time/gas valves.