Gunsmithing Quick 308 twist question!

[PatrickChewing]

Hey guys,

I'm in the process of gathering parts for a shorty 308 build. I plan on using FGMM 175g as my primary choice of ammo and will be shooting mostly with a suppressor. Im thinking about going with a 18-20 inch barrel. My question is should I go with a 1/11.25 or a 1/10 twist?

Thanks in advance for your help!

Clay

 

[Graham]

Re: Quick 308 twist question!

How far do you plan to shoot? Where do you plan to shoot?

For an 18" barrel I would go with a 10-twist. For a 20" barrel 11.25 should be fine.

 

[jonaddis84]

Re: Quick 308 twist question!

Go 10, Im sure youll want to shoot subsonics at some point

 

[Graham]

Re: Quick 308 twist question!

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: jonaddis84</div><div class="ubbcode-body">Go 10, Im sure youll want to shoot subsonics at some point </div></div>Good point. A 10-twist should get you up to 200s, maybe 220s in subsonic. For 240s you will need a 9-twist.

Don't sweat the supersonic twist rate, though. A lot depends on the barrel. I have a 12-twist that shoots 180VLDs quite well in winter.

But if you want to shoot at near-transonic ranges with an 18" barrel you will probably be happier with the 10-twist.

 

[JJones75]

Re: Quick 308 twist question!

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: PatrickChewing</div><div class="ubbcode-body">Hey guys,

I'm in the process of gathering parts for a shorty 308 build. I plan on using FGMM 175g as my primary choice of ammo and will be shooting mostly with a suppressor. Im thinking about going with a 18-20 inch barrel. My question is should I go with a 1/11.25 or a 1/10 twist?

Thanks in advance for your help!

Clay </div></div>

Error on the side of caution in case you want to stretch it out to 1000 or if you want to shoot heavier bullets. I shoot 175gr SMK (Cor-bon loads) to 1k out of a 16" 308

 

[PatrickChewing]

Re: Quick 308 twist question!

Thanks for the info guys. So it looks like I should go with a 10 twist.

 

[TxShooter63]

Re: Quick 308 twist question!

There is a big difference between 18" and 20". Some companies are selling pre-threaded 18" barrels with 1:8 twist. The laws of physics apply even on SH. An 18" barrel is going to be reliable to about 600-700 yds. A 20" will get you out to 800 yds with repeatable performance. I am not going to argue with those who claim otherwise, the laws of physics are what they are. If you are staying within 800 yards and want to shoot the 18" barrel you may want to go lower than 1:10. The increased twist will help stabilize the bullet through the transonic range which you will most definitely be in at those ranges with that length of barrel. Suppressors can typically lower velocity by about 50fps and if you go 18" you will be struggling with velocity already so that is something to consider. Again, there is a big difference between what an 18" and a 20" will do. I have experience with both....

 

[Graham]

Re: Quick 308 twist question!

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: TxShooter63</div><div class="ubbcode-body">The laws of physics apply even on SH. An 18" barrel is going to be reliable to about 600-700 yds. A 20" will get you out to 800 yds with repeatable performance. I am not going to argue with those who claim otherwise, the laws of physics are what they are.</div></div>What is the penalty for breaking the laws of physics? Because my 18.5" .308 regularly shoots 1.5 MOA at 1000 with factory ammo here in Michigan.<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: TxShooter63</div><div class="ubbcode-body">If you are staying within 800 yards and want to shoot the 18" barrel you may want to go lower than 1:10. The increased twist will help stabilize the bullet through the transonic range which you will most definitely be in at those ranges with that length of barrel.</div></div>Stay away from a 9-twist. You won't be transonic within 800 yards, even at sea level and especially in the south. You don't need anything faster than 10-twist for anything but specialty applications of a .308.<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: TxShooter63</div><div class="ubbcode-body">Suppressors can typically lower velocity by about 50fps</div></div>Since when? Because I am getting a velocity increase of about 20fps.

 

[angsniper]

Re: Quick 308 twist question!

I shoot out to 1k regularly with an 18.5" barrel.

 

[JJones75]

Re: Quick 308 twist question!

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: TxShooter63</div><div class="ubbcode-body"> Suppressors can typically lower velocity by about 50fps and if you go 18" you will be struggling with velocity already so that is something to consider. Again, there is a big difference between what an 18" and a 20" will do. I have experience with both.... </div></div>

Ive never seen a suppressor drop velocity , ive seen most give a slight increase commonly known ans suppressor boost and in some cases when shooting subsonics very close to super sonic speed un suppressed the can will actualy give enough "boost" to bump them super sonic.

 

[varmint slayer]

Re: Quick 308 twist question!

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: TxShooter63</div><div class="ubbcode-body">There is a big difference between 18" and 20". Some companies are selling pre-threaded 18" barrels with 1:8 twist. The laws of physics apply even on SH. An 18" barrel is going to be reliable to about 600-700 yds. A 20" will get you out to 800 yds with repeatable performance. I am not going to argue with those who claim otherwise, the laws of physics are what they are. If you are staying within 800 yards and want to shoot the 18" barrel you may want to go lower than 1:10. The increased twist will help stabilize the bullet through the transonic range which you will most definitely be in at those ranges with that length of barrel. Suppressors can typically lower velocity by about 50fps and if you go 18" you will be struggling with velocity already so that is something to consider. Again, there is a big difference between what an 18" and a 20" will do. I have experience with both.... </div></div>

^^^^^ Not one word of truth in that post..

FTW...

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[TxShooter63]

Re: Quick 308 twist question!

"I am not going to argue with those who claim otherwise, the laws of physics are what they are."

 

[varmint slayer]

Re: Quick 308 twist question!

It's not a claim. Video of an actual guy doing it....

You've been proven wrong. Just admit it..

 

[seanh]

Re: Quick 308 twist question!

Due to the limited powders available, at one time barrel length determined velocity. Now, if you have a short barrel, there is a proper powder to makeup for the difference in barrel length...Varget for example.

With Varget, your 18-20" barrels are getting the same velocity as the 24" barrels and if you have a 24" barrel and use Varget the difference in velocity is much smaller than it used to be.

So basically you simply load for your barrel length.

As to twist...depends on the bullet you want to shoot. If all you care about is 175's a 12" twist will do it out to 1K, 11.25 just a little better...10" not necessary.

So what do you do if you get a 10" and find that the 175's are not doing what you want at long range? Simple, find the 175's that are designed for 1:10" twist barrels

Oh, and on that GAP with a Bartlin bbl...it's short throated and tight bored to bring up the pressures to increase the velocity...just adding internet conjecture.LOL

 

[aqualung]

Re: Quick 308 twist question!

In similar vein, I just got a nice little Howa 1500 with a fluted 20" 1:10 barrel in .308Win
Plan on loading 168SMK's. IMI brass, Federal GMM primers.
Powders available;
RL15 / 17 / 19
Varget
H414
Vhit of various speeds, from .223 (Vh120/133) up to .300WM (Vh560)
IMR4064 4350

That's just from memory.

So what would be a good starting load for the shorty pipe?

All my other rifles have 24-28" bbls, so short is new for me.

Thanks,

Neil

 

[JJones75]

Re: Quick 308 twist question!

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: TxShooter63</div><div class="ubbcode-body">"I am not going to argue with those who claim otherwise, the laws of physics are what they are." </div></div>

Not wanting to argue but I fail to see where you have made any substantial proof that physics have anything to do with you claim.

I have been in the 1000 yd pits when guys were shooting short barreled (18") and some longer but suppressd and unsuppressed as well as a couple 300 mags , ALL the rounds comming through the targets were making a sonic crack indicating that the bullets were still flying super sonic.

Making a claim based on some math that you have no numbers for calling it physics and stating that this is it no matter what is arrogant and indicates you have no place stating "facts"

 

[Graham]

Re: Quick 308 twist question!

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: JJones75</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: TxShooter63</div><div class="ubbcode-body">"I am not going to argue with those who claim otherwise, the laws of physics are what they are." </div></div>Not wanting to argue but I fail to see where you have made any substantial proof that physics have anything to do with you claim.</div></div>According to his profile he claims to be a firearms instructor.

 

[stangfish]

Re: Quick 308 twist question!

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: TxShooter63</div><div class="ubbcode-body">"I am not going to argue with those who claim otherwise, the laws of physics are what they are." </div></div>


Paul, I have been adamant about things in the past myself and proven wrong. No big deal. I think it is fair to say that older barrel/chamber dimension ideology had created a wall. Thanks to a new mindset we are seeing the barriers of short barrels with regards to velocity, being advanced.

 

[TxShooter63]

Re: Quick 308 twist question!

Ok, guys. My statements are based on my experience using factory Black Hills ammo. Barrel length effects velocity and spin stability. If you are able to over come those with custom handloads then you may indeed be able to effectively shoot past the limitations mentioned in my post. I have never seen a suppressor increase velocity but that doesn't mean it can't happen. We all come on SH to share "our" experience. Yours may vary.
As far as my qualifications all I will say is that I live on a 1600 yard range and I am very fortunate to get to shoot more in week than many do in a year. That does not mean that my experiences are accurate for every situation. I can only share what I have experienced and what is fact. What is fact is that as you shorten the rifle barrel, all things being equal, velocity and spin stability will decrease. This lowers the ballistic coefficient which makes the round less accurate at distance. Those are statistical facts. If you can overcome that loss in velocity through handloading then you can achieve better results than what I have personally seen or what are considered typical, if typical exist in long range shooting. Sorry for the confusion on my original statement.

 

[Niles Coyote]

Re: Quick 308 twist question!

Tx I would highly recommend reading one of Bryan Litz’s books.

http://www.appliedballisticsllc.com/Book.htm

 

[bohem]

Re: Quick 308 twist question!

The 175SMK will fly well all the way, as long as you can possibly launch it with the 1:11.25 rate barrel.

The benefit to going with the 1:10 rate for this setup is if you ever want to shoot heavier bullets like 190's, 200-210's, etc. over something like RL17 OR if you're going to shoot subsonic ammo and you want more than the 180RN for bullet mass on there.

There's so much bad information in this thread about stability and barrel lengths as they relate to twist rates it is just staggering, I'm not even going to engage it.

My advice is to shoot the 10tw to make it simple right now.

Benefits:
You can shoot heavies later if you want
You can shoot subsonics later if you want



If you go with the 11.25tw you can still shoot subs to about 180gr and the 190 SMK sometimes will stabilize. The 10 gives you future flexibility for longer, heavier, slower bullets.

 

[TxShooter63]

Re: Quick 308 twist question!

Niles, I have read both his books many times and I use them as the basis for all of my long range courses. Every statement I made is in alliance with standard ballistic behaviors.

 

[EXTREMEPREJUDICE]

Re: Quick 308 twist question!

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: TxShooter63</div><div class="ubbcode-body">"I am not going to argue with those who claim otherwise, the laws of physics are what they are." </div></div>

Based upon the body size, weight, wing area and speed of rotation, and overall aerodynamics, according to physics the bumblebee shouldn't be able to fly. Nonetheless, the bee doesn't know that and flies quite well anyway!

 

[SuburbanHick]

Re: Quick 308 twist question!

call the bullet makers.... i did....they all said up to 175 11.25 is fine...... 10 is for heavy bullets(175+)

 

[8up]

Re: Quick 308 twist question!

I get the fastest twist I can get. For .308, 10 twist it is. I have been eyeing a 8 twist for a .308 future build.