Thread: Subsonic load for 308

I realise each rifle is different but im after a starting point for some load data for subsonic loads in the 308.

Im after some loads for the 208gr and 212 projectiles I have if they don't sell.

Has anyone got a starting load for the 308 using either trail boss or even any of the ADI powders or pistol powders.

Any help would be appreciated. Cheers.

With cast 151gr bullets my 1:12 twist 24 inch barrel is subsonic at 7.5 grains of Trailboss. My 1:8 twist 16.5 inch barrel is 8 grains.
I have some 190gr Sub-X loads but can't get to the range until level 2, I've started at 9 grains for them assuming they will need a bit more push being heavier and jacketed.

I run a 308 with 1-8 twist 18” barrel
151g cast is 1000fps with 7.2grains of trail boss
168 Lehigh projectiles are 1000fps with 9 grains of trail boss

Casts are great for possums and pests round camp and the Lehighs are awesome on big game

You will probably find that closer to 10 grains is sub sonic for an over 200 gr projectile. Just have a play around, that's what reloading is all about.

Tikka 308 with 18" barrel. I use 151gr casts and 7.5gr trailboss. Comes in at about 1040fps.

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8g trail boss with 151 and 170g cast is subsonic in my 16in A7

It’s a really easy process @jim160. Load up five cases that span the point at which you think you’ll break the sound barrier. Work backwards, i.e. heaviest load to lightest load, and listen for the supersonic crack. It will suddenly disappear. Congratulations, you’re subsonic. Now drop your load to 0.2gr below that, to be consistently below the sound barrier. You’re aiming for about 1,000fps.

Crimping cast lead bullets is essential to maintain consistent pressures.

As Gkp says, your load will be higher than those suggested for lighter bullets. I would start at 10gr and work back in 0.3gr intervals to 8.5gr, you’ll find it somewhere in there.

Greetings All,
What an excellent thread. I have a .308 in the cupboard that does not get out much. It has a 10 power Bushnell scope with target turrets so swapping loads and zero's should not be a problem. There are also some cast and plated projectiles on the shelves so a cup of coffee and out to the shed. Thanks Jim160 and others.
Regards Grandpamac.

Originally Posted by mimms2

And since it hasn't been mentioned, do the testing WITHOUT a supressor. If you get em tumbling, you can kiss your can (or at least a few baffles) goodbye.

Shooting over a chrony is more reliable than listening for the sonic crack, and will give you more data to work with and you can aim for 1040-1090FPS depending on altitude and weather.

I've been lucky so far with the 300blkout. They tumbled but luckily didnt hit the suppressor.
Will load some up and shoot to see if they tumble. Then I will shoot through the chronograph to check velocity.

Would be hard to hurt yourself or even your rifle with trail boss
Start with a full case (not compressed) and work down till you get what you want over the crony
That’s actually what the Instructions say on the website
Its Opposite to other powders as you work down not up

Originally Posted by grandpamac

Greetings All,
What an excellent thread. I have a .308 in the cupboard that does not get out much. It has a 10 power Bushnell scope with target turrets so swapping loads and zero's should not be a problem. There are also some cast and plated projectiles on the shelves so a cup of coffee and out to the shed. Thanks Jim160 and others.
Regards Grandpamac.

Yep. Bushnell elite 4500 on my 308. I zero at 100 with 168gr fiocchi exacta then dial up 8moa to zero at 25 for the subs. It makes for a good day out.

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Originally Posted by jim160

I've been lucky so far with the 300blkout. They tumbled but luckily didnt hit the suppressor.
Will load some up and shoot to see if they tumble. Then I will shoot through the chronograph to check velocity.

Got a recipe for 300blk? Ive got the howa mini action in that calibre and want to make it a pure subsonic rifle.

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Originally Posted by aetchell

Got a recipe for 300blk? Ive got the howa mini action in that calibre and want to make it a pure subsonic rifle.

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Not yet. Was getting there but there was the lockdown so haven't got anywhere yet. Had issues with them tumbling so need to sort them out first.
Have some 150s loaded up to see if they stabilise

Tested the loads today. The 208gr subsonic tumbled but did group at 25m. The supersonic 208gr ones worked fine.

The 150gr flat tip projectiles plus the 150 cmj ones worked as usual. Chronographed at 1030fps.

The 174gr cast grouped with 8.7 & 9g of trail boss.
Will chronograph them at some stage and get them in the right speed range.

Then zero at 50m with drop chart for 25m to 100m.

The 300blkout stabalised as well and were very quiet. Will need to chronograph them.

At least I have a decent start point.

Originally Posted by aetchell

Got a recipe for 300blk? Ive got the howa mini action in that calibre and want to make it a pure subsonic rifle.

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@aetchell I will give you a start point with mine, but your barrel length and wear will show different speeds.
Most factory subsonic loads were for the short barrels on ar15s and were supersonic in longer barrelled rifles.

But will let you know. I think the powder used is 2205.