My 300blk will not cycle subsonic ammo (I've tried 5 different reputable commercial loads). It appears to be significantly undergased, It just won't chamber a subsonic round after the first one is fired. Supersonics run flawlessly. Aero upper, BCM BCG and carbine buffer tube, YHM 9.1" barrel, AAC 7.62 sdn can.

I've tried all buffer weights and Sprinco carbine springs but no joy. I'm strongly suspecting the YHM barrel port is undersized plus the muzzle threading is flawed so my Geissele Suppressor Alignment Rod barely clears the exit hole of the can. I've always been satisfied with YHM product but this barrel isn't getting it done.

I'd want to replace the YHM barrel with a sub 10" Noveske but they are currently unobtainable. May anyone recommend a sub 10" barrel the will run subsonics with the 7.62 sdn can?

Regards,
mLee

Seekins would be my choice.

That's what I have. Replaced a CMMG that had a bad gas port.

Can you open up the gas port? What mags are you using? Flat nose subs don't feed out of my lancers in either of my blackouts

Years ago Noveske barrels were unobtanium when I built my .300.  I found a brand new one on the EE, I was very lucky.  8.5" and works perfectly with everything I load for it, subs and supers.  The Noveske came with a low pro gas block and tube.  There was a solid steel dowel type pin for the gas block and the barrel was pre-drilled, so there was absolutely no doubt about getting it lined up.

I use it with or without a Gemtech HVT, but mostly with.

I do recall I used one powder that it was completely incompatible with in a sub, but luckily it was a small test batch.

Can anyone drill your port a bit bigger for you?  I wouldn't suggest doing it yourself, because I could easily see a bit snapping off in the hole.

ADCO can probably cut and thread their 10.3" DD barrel to a suitable length.  They did a short 9mm barrel for me when I couldn't find one anywhere.  Call them.

If you can find an Advanced Armament Corp 9" barrel, I'd suggest that.
Mine has a gas port size of .098" and has run everything I've put through it.
I'd measure your gas port and drill it out if it's smaller than .098".
Good luck!

It’s easy to drill out a gas port a drill size at a time. Inserting brass or wood dowel into the bore stops the bit from going into opposite wall of bore.   I’ve seen it done at the range with just a portable drill.

Q shows that their Honey Badger barrel assemblies are in stock.  I've been super pleased with mine.

https://www.liveqordie.com/products/honey-badger-barrel-a