Hi guys. Has anyone had any experience with a 1 in 7 twist .308 barrel? Probably 18 inches. Some subs but mostly 168gn and higher supersonic loads.
Thanks in advance.
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Hi guys. Has anyone had any experience with a 1 in 7 twist .308 barrel? Probably 18 inches. Some subs but mostly 168gn and higher supersonic loads.
Thanks in advance.
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Why 1 in 7"?
I used to own an old Rem 788 with a Douglas 1:8 twist years ago...and that would be the fastest twist I would go. It was great with subsonics but found that it was very fusy when working up high velocity handloads. It didn't take much to hit high pressures of blown primers and that's the problem. With the larger diameter and heavier .308 bullets where it takes more force to go to full rpm in a high velocity load, you can reach too great a pressure just too easily in a tight twist barrel (in my experience)
1 in 8 seems to be the standard rate for subs in 308. I'm sure a 1in 7 would still work. As above you'll find pressure a bit earlier, and i probably wouldn't be running 125's through it
you will also tear apart soft projectiles if you drive them at high velocity...the RPMs will just be too much for them....BUT flip side of that is that a projectile should open up well at less than full speeds.
Cheers everyone. Sounds like id be better off with a slower twist. Just had the option of a 1 in 7 to try.
Thanks again.
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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.
for short barreled subsonics up to 1-5 work great
1-5 seems to be the standard these days for the machined expanders and works just fine with supersonic
the extra rotational energy is bugger all but it gets the expanders spinning like an outboard propellor inside the target giving you a bit more energy transfer
you can go slower twist if your barrel is longer
the fastest barrel I could get in NZ was a 1-8 trueflight at the time and I am very happy with it, I would prefer faster but this is a great barrel that shoots fantastically
mine is 300blk just for subsonics
this too fast twist thing isnt the issue that its made out to be from the research
select your barrel up to stabilise the longest bullet you plan to run, but long story short 1-7 will be about as good as you can get and 1-8 will be a lot easier to find
if you can import a barrel from x-caliber barrels in usa you can get the 1-5, and pacnor did 1-6 before they burnt down and are apparently nearly rebuilt so should be making barrels again soon
I ask a lot of questions to Kevin brittingham from Q on instagram because they seem to be the cutting edge of subsonics with discrete ballistics
its wort the watch to get your head around these things
I used a 1-11 308 tikka t3 barrel full factory lenght for shooternz's 151gr cast bullets for ages before going fancy with 300blk
to be honest it is basically exactly the same outcome with the same noise but now at least i get to carry something short and light
Attachment 146034
I read your Initial message wrong, If its only some subs whatever barrel twist that is reccomended for the 168+ gr will do good enough for sub use
1-7 or 1-8 would be great in your application 1-5 is pretty much just for short barrel subsonic dominant guns (which is my current obsession)
Bill999 I just can't agree on your choice of 1:5" for sub and supersonic, and your statement that in a longer barrel you can use a slower twist rate.Quote:
Originally Posted by Bill999
A twist rate of 1 in 5 means the bullet turns 1 full rotation per five inches of travel. A 1 in 8 twist means the bullet makes one revolution every eight inches of travel (it has to travel more distance to make a full rotation). But adding length to the barrel ie going from a 16" bbl to a 24" bbl will not make the bullet rotate faster than 1 time per 5 or 1 time per 8 inches of travel (whatever is the barrels twist rate).
The only way a longer barrel could make the bullet rotate faster is that it has more internal space for powder to convert into expanding gas/pressure therefore velocity can increase. But that is mostly theoretical as one generally cannot reach safe pressures to increase the velocity enough to get RPM in a 1 in 8" twist longer barrel equal to a 1 in 5" shorter barrel.
So to summarise: spin is dictated by the twist rate of the rifling, no matter the length of the barrel. 1 twist in 8" is the same from a 16 " barrel as it is from an 18", 20" or even 24" barrel... one complete rotation of the projectile every eight inches. Really the only practical variable that will affect RPM is the rate of twist... not barrel length.
Im not sure what we dont agree on, most of what you are saying is spot on
the bullet isnt getting rotated faster in the longer slower twist barrel(quite the opposite), it just has more time 'in barrel' to stabilise so has less issues
have a look what the company that makes the "fix" by "Q" and the "Honeybadger" 300blk run 1-5 for sub/super use, and 1-7 or so for 308
the typical barrel lenght is 5-7 inches for these guys for 300blk and 12-14" often for 308s
its cool stuff
Greetings All,
There has long been, in the US, a fear of projectiles being over stabilized resulting in poor accuracy. This may have had some basis years ago when projectiles were poorly balanced. Today almost all projectiles are of much better quality and fast twist has little if any effect. Still, however the myth persists. Twists in my .308 rifles run from 10 to 14 inch twists and generally shoot most projectiles well. One with a long throat does not shoot 150 grain boat tails well but shoots 150 grain flat base really well. I have not tried subs yet but will. Another .308 I am aware of with a 7 inch twist shoots everything well, including subs.
Regards Grandpamac.
Allways appreciate your input @grandpamac . Cheers. I have committed to a 1 in 7 so looking forward to seeing how it shoots.Quote:
Originally Posted by grandpamac
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Lowdown on twist rates affecting velocity -
How Muzzle Velocity Changes with Different Barrel Twist Rates « Daily Bulletin
Also a comment from another forum by Frank Green (co owner of Bartlein Barrels) -
"Not only did we make all those barrels in the test but we chambered them as well. So same chamber reamer was used in all of them and the barrels where all made at the same time. If I recall correctly all of the barrels where made out of the same lot of material except for the left hand twist was out of a new lot. So about as identical as you can make them.
It's always been my understanding that twist might have a small impact on velocity but for the most part it really doesn't in the grand scheme of things."
If you want to use cast bullets don't use a fast twist the slower the better my test rifle has a 1:13" twist and stabilises the 151HP down to 900 fps
haven't tried to go lower not keen on a stuck bullet.
I saw those videos regarding the q rifle and the 8.6 creedmoor ( more or less a 338 whisper or br which out the trade name ).
Ask @Wingman what was the twist rate of his 338br and what projectiles he was shooting subsonic and how they where flying.
For the majority of what we are doing , I don't think that super fast twist are of any use.
Overstabilising at a rate of 1 in 5 twist might cause some failures in conventional cup and cord projectiles specially if flying at supersonic speed.
When I started f class shooting in early 2000, I remember very well the competitors having the old 7mm a-max exploding in mid air when launched from a 1 in 8 twist with a fast 284 win or a magnum. Not all of them but 1 or 2 out of a series of 12 or 15 was enough to make it to the bottom of the scoring board.
The 6mm ppc and 30 br and their wildcat cousins still win matches with 1 in 14 and 1 in 17 twist respectively.
Why is the venerable 22 lr still flying so well in 1 in 16" twist?
My .338 Whispers ran 1-9" twist Shilen and trueflite barrels shooting 300gr SMKs and 300gr Berger hybrids at 1040fps MV.Quote:
Originally Posted by Friwi
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?
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.Quote:
Originally Posted by HandH
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...
Greetings Mauser 308,Quote:
Originally Posted by Mauser308
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?
I don't know about the twist rates for subsonic rounds, but I am surprised that 1:7 or 1:8 are recommended.Quote:
Originally Posted by shooternz
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
I have to know how much drop for 1000y ?Quote:
Originally Posted by Wingman
What optic setup were you using to get enough up?
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.Quote:
Originally Posted by Matt308
180grn winchester power points...all day long for bush load....Quote:
Originally Posted by HandH
+ 1 my 250 gr soft points traveling around 2850 fps drop 10 mtrs at 1000 mtrs.Quote:
Originally Posted by veitnamcam
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.
Amazing how little FPS the subs lose(or perhaps rather how much the supers lose?)Quote:
Originally Posted by Friwi
@Friwi can you give more details?Quote:
Originally Posted by Friwi
I'm surprised that the velocity loss is only 200 fps over 1000 yards.
My observations with lighter projectiles over 1000 yards is that the velocity drop is 1200 - 1400 fps, not 200 (starting between 2800 and 3000 fps).
Subsonic don't slow down anywhere near as much as supersonic, surprised me when I found out, but all the info and ballistic apps agree.Quote:
Originally Posted by Cyclops
If a sub slowed by 1200-1400 fps it would be coming back at ya!
