twist and barrel

[subscriber]

Barrel maker's twist calculator: http://www.mcgowenoutlet.com/popupcalculator.html

[Vu 308]

Neither statement is true. We shoot 30" barrels, with bullets that are fast and accurate.

True story.

My FT-R rig has a medium palma barrel at 30".

If you think light barrels don't work well for accuracy, come out to a HP/F-Class match.

[Vu 308]

More details please.

What is your barrel contour?

Are you shooting factory ammo or only custom reloads?

What bullet weight are you using at what velocity? If 155 grain, I would be surprised if they are going over 2900 FPS.

Is your barrel bedded or free floating?

Lane is rocking a Medium Palma

Hand loads

I guess you are surprised then because these guys are lobbing 155s at 3000+

Some free float, some use a barrel bad, all my guns are free floated.

[Vu 308]

In a .308 without a 30" barrel the 175 will outperform a 155 with significance at 600 yards.

*buzzzzard* wrong.

155s from a 26" 11.25 twist pushed hard will smoke a 175.

We have a few guys pushing 155s at 2900 out of short barrels with a whole lot of H4895.

That being said, they are the same ones that smoke a 308win barrel in 3000 rounds.

[HK Dave]

Lane is rocking a Medium Palma

Hand loads

I guess you are surprised then because these guys are lobbing 155s at 3000+

Some free float, some use a barrel bad, all my guns are free floated.

We talking scenar? Wow 3000fps is awesome.

Ever heard of anyone doing that with Varget out of a 26"?

[Vu 308]

HK Dave,

Yes, we had this one guy Jason rocking a 155 scenar with a LOT of varget in his 11.25 twist 5R at 2950. He was keeping up with my 260 @ 1K.

Burned his barrel out in 3000 rounds, and brass didn't last for nothing.

It is doable, but why ya know? Just rock a 260rem or 6mm if you want a go fast rig.

[milotrain]

*buzzzzard* wrong.

155s from a 26" 11.25 twist pushed hard will smoke a 175.

We have a few guys pushing 155s at 2900 out of short barrels with a whole lot of H4895.

That being said, they are the same ones that smoke a 308win barrel in 3000 rounds.

That's true when you get the 155s up around 2900+ and you run the 175s at reasonable speeds. Other than the fact that it's not an apples to apples comparison I don't really consider blowing primers and toasting brass on single firings as standard or recommended operating procedure. But I also shoot service rifle where you can't get those speeds with a 155, so we use 175s at 600.

[HK Dave]

HK Dave,

Yes, we had this one guy Jason rocking a 155 scenar with a LOT of varget in his 11.25 twist 5R at 2950. He was keeping up with my 260 @ 1K.

Burned his barrel out in 3000 rounds, and brass didn't last for nothing.

It is doable, but why ya know? Just rock a 260rem or 6mm if you want a go fast rig.

I agree is rather run 6.5 creed or something but to know someone is running a 308 to compete with 6.5 is pretty cool.

[Vu 308]

^ exactly.

That being said, those 155s at those speeds have a fair amount of recoil so shooting those loads off barricades and in dynamic COFs where you need to spot your miss and make a correction can be a PITA.

I will take a 6.5CM over a 155 at mach 2 any day of the week.

Milo,

We don't destroy brass on one or two firings. You may get 4 to 5 at those pressure levels though.

That being said, DO NOT TRY this in your factory M700, you will not get these speeds with factory tubes. And always work your way up to any load.

[RobertMW]

Whoa whoa whoa... rather than turn into typical calguns "what is the best bullet"... Why don't you keep helping the OP here.

Two things I haven't seen obviously pointed out here:

1. If you have way too fast of a bullet spin, when your round gets to extreme ranges (supposing you are shooting to them), your bullet has slowed down significantly due to drag, but your bullet's spin velocity is hardly touched. This creates a point where your bullet gets OVER-stabilized and will no point towards it's direction of travel, causing it to veer off course in very difficult to predict directions.

2. If you have a high twist barrel, you are putting higher loads on your barrel to get the bullet to spin at greater RPM, thus you wear out barrels faster when you push your velocities up.

[subscriber]

Lane is rocking a Medium Palma

Hand loads

I guess you are surprised then because these guys are lobbing 155s at 3000+

Some free float, some use a barrel bad, all my guns are free floated.

Thanks. I stand corrected.

That said, I think the OP was probably asking about twist in the context of factory rifles and standard off the shelf ammo. What twist would you recommend for factory rifles?

[toby]

[QUOTE=milotrain;13790478]It's not that they are not effective or fall out of the sky, it's that when you are fighting for xs the 175s buck wind better. Implying I don't shoot "in real life" is both childish and incorrect.[/QUOTE]

Did I say you did not shoot real life?...No I said I shoot real life meaning by experience and seat of the pant's learning and not by the internet, ballistic calculators, mildot's, rangefinders, wind meters, ect ect. I learned the hard way and still practice and teach that way. Whatever rings your gong!

[milotrain]

Yes you did. That's what you imply when you say "Nope, I shoot real life." you can backtrack if you like and say that's not what you meant.

This thread is becoming daykare.

[LynnJr]

Toby when Milotrain posted earlier he was talking about ahnother8 and not you.

To the OP
Don Millers easy to use formula coutesy of Precision Shooting Magazine

S = (30*m)/(t^2*d^3*L*(1+L^2))

S is the gyroscopic stability factor. This is the measure of static stability and 1.4 is the minimal (optimal) value.

m is the bullet weight in grains

t is the twist rate in calibers per turn (for example, a 1:13" twist .308 barrel has t = 13/.308 = 42.2 calibers per turn.

d is the bullet diameter

L is the bullet length in calibers.

This equation is very accurate for a wide range of bullets, velocities and twists. There are corrections for non-standard atmosphere and velocity corrections (the equation is built around MV = 2800 fps). The effect of different muzzle velocity is not as important to stability as most people think.

If you want to shoot a 240 Sierra MatchKing out of a 300 Whisper at 800 fps you would use a 8 twist barrel likewise the same bullet in a 300 Weatherby magnum at top velocity would still use a 8 twist barrel.

Barrel length has no significant affect on twist rate.If you look at the formula barrel length doesn't matter and isn't even in the formula.Pistols shoot and they shoot very accurately and most don't have 6 inch barrels on them.

As you increase the twist rate for a given velocity the bullet spins faster.If your bullet has any imperfections or imbalances they are amplified exponentially as RPM is increased and gilt edge accuracy suffers.This only means something to competition shooters and explains the whole over-stabilization theory.

For Joe Q Public a 308 in 10 twist will work for most anything.
For a competition shooter they already have all of this figured out.

[Pthfndr]

That said, I think the OP was probably asking about twist in the context of factory rifles and standard off the shelf ammo. What twist would you recommend for factory rifles?

Actually that's not at all what he asked. So everyone's input is valid.

His first to posts in the thread.

I see online most stock .308 with a twist of 12, but i also see twist variation from 8 to 14 for custom barrels

(italics by me)

I just want to understand how twist works and its implication with barrel and ammo so i can do an educated purchase when i will buy a new barrel or new ammo or reload new ammo, or build multiple rifles for different purpose.