Thread: 308 twist rate

Originally Posted by Friwi

Ask @Wingman what was the twist rate of his 338br and what projectiles he was shooting subsonic and how they where flying.

My .338 Whispers ran 1-9" twist Shilen and trueflite barrels shooting 300gr SMKs and 300gr Berger hybrids at 1040fps MV.
They were still perfectly stable and grouping well with round holes at 1000y.
The team down in the butts nic named it the bumblebee as the bullets whizzed over with a deep buzz at sub speeds rather than the sharp crack they were used to.

I totally agree with @Friwi, all the best accuracy I have achieved with both subsonics and high velocity was a twist rate of "just enough" and faster twists barrels groups have always opened up.

Fast twist barrels in .308 were designed for use with the heaviest and longest jacketed bullets to run at subsonic speeds.
1-8" gives the best subsonic accuracy in .308 with the all the longest and heaviest bullets available such as the 240gr SMK.
1-7" is too fast and groups do suffer.
If you are using cast lead in a 1-7" you will also get a lot of bore leading which also destroys accuracy.
Lighter bullets in a fast twist don't nessisarally shoot slower than a slower twist will but do reach pressure faster which can in turn effect final achievable velocity.

The best twist for that cast 151gr HP at subsonic speeds is a 1-12" to 1-13". They are a short bullet with a blunt nose and base so dont require a fast twist barrel to stabilize them. The slower twist also combats bore leading.

Unless you intend on only shooting specialty machined copper expanding petal type subsonic projectiles and believe the marketing around the rotational energy of such bullet killing game any better than a subsonic soft lead cast HP or a tumbling after impact long 240gr SMK then dont bother with anything over 1-8" twist.

A 1-12" to 1-10" will actually shoot a wider range of subs and high velocitie bullets better than the 1-8" and 1-7".
You can shoot up to 220gr as subs as long as you run the round nose bullets.

So distilling all the experience what factory 308 non subsonic ammo should I be trialling initially in my Bergara 1:8” 16” takedown?

Originally Posted by HandH

So distilling all the experience what factory 308 non subsonic ammo should I be trialling initially in my Bergara 1:8” 16” takedown?

Your 1-8" twist can stabilize a 240gr, so if you wish you could try some heavier bullets to see what they do but just remember they are heavy and will be seated deep into a .308 case so velocity will be low.
I like the 168gr and 175gr as the 308 needs all the help it can get... lol... so going up in weight over 175gr just isn't doing it any favors. For all-round performance, I would get the HORNADY SUPERFORMANCE .308 165GR SST.
The price is about $70 and from your 16" barrel should reach around 2650fps.

Yup so fits with my brief experience with this particular rifle, seems to shoot 150-165 factory fodder pretty well. As mentioned ‘overstabilisation’ not much of an issue...

Originally Posted by Mauser308

Remington have started hanging .30-06 barrels on their .308's so getting more options in 1-10. That for me anyway seems to be the best option for all uses in .308, it will chuck and group with just about anything you would care to chuck out of it.

Having said that I've got an ex-target 1-13 barrel there at 24" long that will stabilise up to 175 and 180gr, which is better than you would expect. I haven't gone heavier as I haven't had the need...

Greetings Mauser 308,
My M700 .308 manufactured Feb 1975 has a 1 in 10 inch twist barrel which was standard for them at that time and for years thereafter. I don't know what twist they use in their SPS currently.
Regards Grandpamac.

Hmm, according to the internet my Finnwolf has a 1 in 12” twist rate, seems slow compared to some of the twist rates mentioned in this thread?

Originally Posted by shooternz

The standard .308 twist is 1:12" some match/Sniper barrels are 1:11" to handle 175 SMK's any faster twist is only for the real heavies like 230 grains
if you only plan on using subs occasionly it would make sense to build it to handle the 150 to 180 grain bullets that are the standard for the .308
subs only have a limited range no matter how streamlined they are they drop like rocks.

I don't know about the twist rates for subsonic rounds, but I am surprised that 1:7 or 1:8 are recommended.
I'd have thought this was too fast.


I'm a target shooter. I get my 308 barrels in 1:10, 32".
I shoot 155 gr and 185 gr projectiles with the 1:10 barrel, knowing they will shoot heavier if I wish.

My first 308 barrel has fired over 6,000 155 gr projectiles and is still very accurate.

Hi Handh,
I am thinking of getting a bergara takedown in 16 inch..... have you shot 150gr supers out of it?
If so how do they go?
Regards
Matt

https://www.youtube.com/watch?v=UdM6...IndicatingDogs awesome video covers most of what your asking about

Originally Posted by Wingman

My .338 Whispers ran 1-9" twist Shilen and trueflite barrels shooting 300gr SMKs and 300gr Berger hybrids at 1040fps MV.
They were still perfectly stable and grouping well with round holes at 1000y.
The team down in the butts nic named it the bumblebee as the bullets whizzed over with a deep buzz at sub speeds rather than the sharp crack they were used to.

I have to know how much drop for 1000y ?
What optic setup were you using to get enough up?

Originally Posted by Matt308

Hi Handh,
I am thinking of getting a bergara takedown in 16 inch..... have you shot 150gr supers out of it?

If so how do they go?
Regards
Matt

Sadly I don’t have enough objective experience to comment but the midweight factory eg 150-165s seemed surprisingly accurate for a break action cheapy.

Originally Posted by HandH

So distilling all the experience what factory 308 non subsonic ammo should I be trialling initially in my Bergara 1:8” 16” takedown?

180grn winchester power points...all day long for bush load....

Originally Posted by veitnamcam

I have to know how much drop for 1000y ?
What optic setup were you using to get enough up?

+ 1 my 250 gr soft points traveling around 2850 fps drop 10 mtrs at 1000 mtrs.
Be very interesting to know how much the subs drop....

My ballistic software told me for a 300 gr SMk launched at 1040 fps and zero at 100y:

-1723 inches of drop ( or 162 Moa of elevation to click up).
3.3 second of flight time and a remaining speed of 833fps on arrival.

Originally Posted by Friwi

My ballistic software told me for a 300 gr SMk launched at 1040 fps and zero at 100y:

-1723 inches of drop ( or 162 Moa of elevation to click up).
3.3 second of flight time and a remaining speed of 833fps on arrival.

Amazing how little FPS the subs lose(or perhaps rather how much the supers lose?)