Any one worked up subsonic 308 loads?

As i wait for my can i wanted to go ahead and do some research on loading some subsonic ammo.

Im already loading 175 smk .

So with that being said, any load data or personal exp would be nice hear.

I've experimented with .308 subs, with almost consistent failure.

I first tried out 220gr SMK's, with the intention of having them be "good enough" at 100 yards. With a 1 in 12" twist, I was still seeing tumbling and inaccurate groups at 100 yards. I gradually lowered the bullet weight, expecting the twist rate to be mitigated by the smaller, shorter bullets. While tumbling went down, accuracy and consistency did too.

With the minimal volume of powder that I was loading (IMR 4895), I had lots of empty space in the casing, which was leading to a non-uniform burn, as best as I could surmise. I'm talking changes in consistency differing +/- 100fps - some rounds were burning faster, breaking the sound barrier, then crossing the barrier again, and getting increased yaw (tumbling). Others were just not pushing 1000fps, so I was seeing lower than .22 velocities.

My only go-back would be to try a loading with trail boss, and a heavy lead bullet. TB is a very low density powder, and I think you could probably get a 175gr bullet about subsonic. Maybe even a 220gr SMK.

The whole argument has become moot for me now though. .300blk is the right answer for a subsonic .30 cal bullet, and there is a dearth of data out there for loading them. They have a .30 cal twist as well (5/8x24), so you can run suppressed rounds through your blackout, and quiet down your .308. Or run supersonics through your blackout too.

One thing that I would especially caution against is seeing if your can warrantees shooting subsonic .308s thorugh it. Some will explicitly state that you cannot shoot subsonic .308 through the can, because it will have a high risk of baffle strikes.

10-4, good information! Thanks

running 9.7 trail boss with a 180 grain BTHP. my barrel is a 1 in 10
I have not had any issue but run at your own risk and as always try a few rounds to make sure they dont key hole.