Subsonic 308 w/ 168 grain Speer BTHP

[DMW1116]

I found some Titegroup and Speer match bullets. I want to try some subsonic 308 loads just for fun. The only data I’ve seen uses a 168 grain SMK. I’ve generally substituted similar bullets with the exception of Hornady, which I won’t do any more. Any issues with this combination? I plan to shoot them from my AR10 with the gas block closed.

 

[Charlie98]

Just a word of caution… TiteGroup can get spikey, real fast… but you prolly know that.

Do you have data to start with?

 

[DMW1116]

I was planning on using the data from Hodgden. 8ish grains of powder and a 168 grain match bullet.

 

[Slamfire]

I should e some Titegroup and Speer match bullets. I want to try some subsonic 308 loads just for fun. The only data I’ve seen uses a 168 grain SMK. I’ve generally substituted similar bullets with the exception of Hornady, which I won’t do any more. Any issues with this combination? I plan to shoot them from my AR10 with the gas block closed.

I found, and it was common knowledge that the 168 Match bullets tumbled going super sonic to sub sonic. They were a complete failure at 1000 yards because the things started tumbling around 800 yards. I think it probable they will tumble at less than 1000 fps, so you might have poor accuracy.

As for powders, that is a tough one since you want to be less than 1000 fps. Any ideas I have, are probably bogus as I have never tried velocities at 1000 fps in a rifle.

by the way, Ed Harris had a reduced "The Load" with Red Dot. https://www.reddit.com/r/reloading/comments/53rav5/the_load_by_ce_harris_an_interesting_take_on/ Might be going faster than you want.

 

[DMW1116]

Like sideways through the target tumbling? Is the problem the low velocity or the transition through the sound barrier? I need to check but I’m pretty sure my barrel is a 1:10 twist.

 

[JeffG]

Reloading can be dangerous even when following published load data, or personal data from other sources. All reloading and firing of reloaded ammunition is done at your own risk. The load data published on this website is intended discussion purposes only and for use by experienced reloaders only.

Having said that:
For my subsonic .308 loads, I use 180gr Sierra round nose, (stability rating of 3.3). It tends to keep the weight bullet forward. A slow bullet tends to have the dynamics of a shuttlecock. You may have to drive spire points a little harder.
I drill out the flash hole to 9/64" and keep them only for subsonic rounds, that's important.
Remember when you ladder for suppressor loads, you work down, not up.
I worked one load down to 12.7 of Unique from 13gr. (about 950fps) My Titegroup load started at 8.5 grs. and I settled at 7.5grs, again about 900fps. I moly coat my suppressor bullets. Be sure to shoot and paper test all loads, suppressor off, to check for bullet yaw and tendency toward tumbling. You want to avoid baffle strikes.

 

[AJC1]

If I were trying to do this I would go with 4227. It's a very mild powder from poof to max pressure, and will give you better case fill than a lot of others. The same powders used in 300bo is probably a decent area to be. I'd also consider seating deep to eat up some case volume. I'd also be using the hottest primer I could find.

 

[JeffG]

I found, and it was common knowledge that the 168 Match bullets tumbled going super sonic to sub sonic. They were a complete failure at 1000 yards because the things started tumbling around 800 yards. I think it probable they will tumble at less than 1000 fps, so you might have poor accuracy.

As for powders, that is a tough one since you want to be less than 1000 fps. Any ideas I have, are probably bogus as I have never tried velocities at 1000 fps in a rifle.

by the way, Ed Harris had a reduced "The Load" with Red Dot. https://www.reddit.com/r/reloading/comments/53rav5/the_load_by_ce_harris_an_interesting_take_on/ Might be going faster than you want.

The instability thing is real. match bullets, spire, and boattail bullets tend to be heavier in the rear. As the velocity slows, so does the rotational rate, either through long yardage or slowing it with a lesser powder charge, the a$$ end wants to go first, and the bullet starts to yaw. If this happens in your can, you will get damage. You can overcome this with a shorter, lighter bullet, or a round nose heavy bullet that resembles a shaft, and has the balance nearer to the front.

 

[jmorris]

Only subsonic 308 I have played with is cast and coated 150’s, for them I would start around 11.0 grains of trailboss and work down (opposite of normal but you are all ready below on pressure and trying to keep from sticking a bullet in the bore).

https://imrpowder.com/wp-content/uploads/2016/11/trail-boss-reduced-loads-r_p.pdf

https://loaddata.com/articles/PDF/LD-36 Haviland LR.pdf

https://hodgdon.com/wp-content/uploads/2020/07/subsonic-data-final.pdf

 

[DMW1116]

I had another thread on spin and how it changes down range. Based on that thread the loss of spin isn’t the reason for long range instability. Also based on the Berger stability calculator these bullets should be stable at the listed velocities. I won’t be using a suppressor at this point. This is just an experiment for fun.

 

[DMW1116]

Were this a manual action I would definitely use cast and coated bullets for this little experiment. However I’ve had to clean barrels from leading and I do not want to repeat that with a gas port or system.

 

[jmorris]

I plan to shoot them from my AR10 with the gas block closed.

That should keep the system clean for sure. How many rounds are you planning on sending down range with your experiment and are there any goals?

 

[DMW1116]

Probably 10 or so rounds is all I have the powder to do. I just wanted to see if it worked at all and see if they would group at 50 yards. I expect 2” groups or so but that would suffice to prove it works. I plan to do the same for 223 and some 55 grain bullets but that will probably work as I’ve seen other people try it.

 

[DMW1116]

Some Trail Boss would be great if it weren’t the powder Sasquatch uses for reduced loads. He uses Varget for full power. All three things (Sasquatch, TB, and Varget) are often talked of but seldom seen.

 

[DMW1116]

I tried these out this weekend. I used a load of 8 grains of Titegroup with the 168 grain Speer bullet. I used some primers I pulled from some messed up 308 factory ammo, so I don’t know what they were.

I think my 2” group at 50 yard prediction was at least close. I got 3/4” at 25 yards. I saw possible signs of tumbling but I need to try again to be sure. The tearing around the bullet hole was asymmetrical but it was always more prominent on the top side of the hole.

For future tests I think I’ll try some 150 grain round nose bullets I have laying around. They’re destined for reduced loads anyway, and shorter so should have better stability. Overall, accuracy is currently better with cast loads in my 30-30. It’s not really worth it to put much more into this but I’ll try a half dozen more for science.

 

[GeoDudeFlorida]

Like sideways through the target tumbling? Is the problem the low velocity or the transition through the sound barrier? I need to check but I’m pretty sure my barrel is a 1:10 twist.

SMK’s need more spin to stabilize. That’s why they typically need to be driven harder, to get the centrifugal forces up. Having said that, I use 180gr SMK’s in .30-30 with 6gr of Red Dot out of a 10” Contender and they are pretty accurate out to 100yds, give or take. I don’t know if they are subsonic necessarily but they were “quiet” for .30-30 in a handgun. I tried the same bullets with Bullseye, Unique and 700X and the results were pretty close to the same. I’m not sure what you will see from .308Win in a Stoner action with a 20” barrel, though.

 

[DMW1116]

I'll probably try three more of these at 50 yards, then maybe try the 150 grain bullets. That round nose won't matter with the distances a 1050 fps bullet will travel. I will probably save the rest of the 150s for some 1600-1700 fps loads from 30-30. Trying for about 1000 ft-lbs muzzle energy. Unless they work super well

 

[DMW1116]

Turns out I’m still a bit brass poor for 308. If I come across more I may revisit this but until then, I know it works. It will need some tweaking for hopefully better accuracy. Right now my cast loads in 30-30 shoot better and are cheaper. If I ever get a suppressor, then this experiment will climb back up the priority ladder.