Anyone else wonder why custom/factory rifle makers are still using a 1-10 twist for the 300 WM?

[Bart B.]

Factory rifle builders and ammunition manufacturers have to follow the Saami specs

Not true at all. From SAAMI:

American National Standard Voluntary Industry Performance Standards for Pressure and Velocity of Centerfire Rifle Ammunition for the Use of Commercial Manufacturers

Members volunteer to subscribe to SAAMI standards, but there many who don't subscribe even when they're members. Velocity and pressure test barrels, for example. There are no SAAMI standards, that, if not followed, are a criminal offence.

For example, SAAMI specs for 308 Win:

*barrel twist is 1:12 inches. Factory barrel twists range from 1:10 to 1:13.

*308 Win test barrel length specs is 24 inches; factory barrels go from 16 to 30 inches.

*barrel bore and groove diameter specs, have a .002" tolerance; bullets have 003". Bore cross section area spec is .0736 square inch minimum. Imagine the peak pressure difference shooting a .309" diameter bullet in a .306" groove diameter barrel and a .306" diameter bullet in a .309" groove diameter barrel. Both bullets' loads had the same average peak pressure in a SAAMI spec test barrel with .3000" bore and .3080" groove diameters. To say nothing about chamber differences or bullet extraction force.

SAAMI has a glossary to standardize terminology to prevent confusion in communications. Some members subscribing to SAAMI standards use 'head space' to define the space between the breech face and case head when the round is forward against its stop in the chamber. SAAMI says that's 'head clearance.'

It's my opinion that because most folks believe 30 caliber magnums need 1:10" twists is because they started out that way over a hundred years ago. Same for 30-06 barrels that started with the 30-03's 200 grain bullets. Doesn't matter that competitive shooters got better accuracy with slower 1:12" twists in 30 caliber magnums shooting 190 to 210 grain bullets. Note the 308 Win and 7.62 NATO ammo was spec'd with 1:12" twists shooting 150 grain bullets 100 fps slower than the 30-06 did. I had a 9 pound scoped 300 Win Mag sporter with a 1:13" twist 26" barrel that shot 180's into MOA at 1000 yards.

 

[M14AMU]

In the final analysis and cutting through all the BS.....what shows up AT THE TARGET for whatever distance being fired is the end all/tell all regardless of whatever twist rate being used! And THAT my friends may not be exactly what is recommended!!

 

[johnfred1965]

From your original post, I believe you are the only one getting their "Panties in a bunch" and "Have a fragile ego"

As to your question: No, I have never wondered about that, at least until now.

According to AB's website ballistic calculator, the 230 OTM at a sedate 2750 in a 1-10 has a SG of 1.5 at sea level, it only gets better at higher elevation. Guess they use it because it works.

Sako makes a great rifle, but if you want to shoot one from the factory, at 2000 yards, you are just a bit crazy.

If you are going to shoot ELR, and have a chance to hit anything, most likely you will build a custom gun. Krieger offers a 1-9 on their website, and if you called them, I believe you can get any twist you want. I really don't see why you are all bent out of shape.

one last thing, in one post you quoted an article by Robert McCoy, and then said your father did it old school. Did you mean to imply he was your father? and if you did, he should have taught you better.

 

[RonAKA]

1:10 twist is the obvious choice for a factory gun in 30 cal. If you go to a custom barrel you can get any twist you want. I don't see what the issue is about. Berger's recommendations are always conservative. They round the number up to the next fastest whole twist number. Also how many really shoot at sea level and 60 F? Also remember that linear velocity of the bullet slows down faster than rotational velocity or spin. Bullets get more stable as they go down range. You always want the slowest possible spin and still achieve stability.

 

[Bart B.]

1:10 twist is the obvious choice for a factory gun in 30 cal.

Even if you want to have best accuracy with 150 to 155 grain bullets shot from 308 Win cases in long range matches?

"1:10 twist is the obvious choice for a factory gun in 30 cal."

...contradicts:

"You always want the slowest possible spin and still achieve stability."

 

[RonAKA]

Even if you want to have best accuracy with 150 to 155 grain bullets shot from 308 Win cases in long range matches?

"1:10 twist is the obvious choice for a factory gun in 30 cal."

...contradicts:

"You always want the slowest possible spin and still achieve stability."

The key part is factory gun. Manufacturers will sometimes give you a choice, but mainly just go for the faster twist...

 

[Bart B.]

but mainly just go for the faster twist...

Yes, so a greater range of bullet weight's will shoot decent.

 

[johnfred1965]

I have read several books with out dated information written by people like my father (from the old school). Bryan Litz and Todd Hodnett seem to have much more contemporary and up to date data and thinking. Remember if you don't shoot ELR than this wasn't for you. Your slower twist may give you world records inside 1k yards but how does it hold up at 1500 and beyond?

I don't know how much 1000 yd competition you have shot, but If I had a rifle shooting world records at 1000, I would not hesitate a second to shoot it out as far as I could find a target!

 

[johnfred1965]

#3-Less inherent accuracy? Really? Why is that? Does it slow it down too much? You must be one of those guys that says "you don't want over spin your bullet". Better to "over spin" a bullet than under spin it. I better toss out this 1-7 twist .308 that I have that shoots .25 min most days.... You will have a better BC with some of the longer rounds. Unless the bullet exits the muzzle and then completely flies apart there is no such thing as over spinning a bullet. Look at the 338 LM. most were made with 1-10 I have even seen them with a 1-12 twist but now some manufactures are making 1-9.25 twist. I believe Litz even raised his minimum SG from 1.4 to 1.5
#4-There are many more shooters using 300WM, Norma Mag, Ultra Mag. beyond transonic than you think.

Ringostar- You are incorrect. You can go to Berger's site and see that they were changed from a 10 twist to a 9 twist.

You need to take that 1-7 308 to every competition you can get to. If you are shooting 1/4 minute most days, you could be in the hall of fame buy the end of the year. I shoot a 300blk subsonic and the 220's work fine in a 1-8. Wonder how far that little thing will carry?

 

[Tommie]

Short neck + OAL limitations = limited bullet length.

Try seating a heavy VLD bullet in a 300 Win Mag. Two things are likely to happen:
1) the cartridge won't fit in the gun's magazine
2) bullet OG will be below the case mouth.

The 300 Win Mag was designed to me a hunting round to compete with the 300 Weatherby which feeds from a standard length action. To this end it succeeded marvelously (although it can't reach Weatherby max velocity). And indeed it has been used successfully in long range competition. But given the OAL limitations, ultra heavy/long bullets are not in the picture for repeaters. Thus, the relatively slow twist.

 

[Bart B.]

Don't forget, folks, most micro group sizes posted on the 'net are the smallest ones fired that happen least often. Like Stinnet's .0077" 5-shot 30 caliber record 100 yard group. He holds no other benchrest records and he's about average of all in the game.

 

[bigngreen]

There is a HUGE difference when you approach and shoot through transonic and shooting inside it, this is often where the wheels fall of so in some ELR accuracy we will over rev a bullet which can definitely effect normal range accuracy but beyond transonic you'll actually group vs spreading lead all over a mountain side, then again if you shoot game with over rev'ed cup and core bullets you'll experience a difference in the mess that it makes so for me the only thing I'll over rev is a gun for ELR shooting, a long range hunting gun I'll stay lower.

 

[Joe Salt]

Guys did it ever occur to anyone that a 30 cal Ten twist barrel will shoot just about any bullet size out there, that one of the reasons weatherby changed from a 1-12" to a 1-10 in there 300WBM.
All my 30's are Ten Twist just for that reason!

Joe Salt

 

[Bart B.]

Guys did it ever occur to anyone that a 30 cal Ten twist barrel will shoot just about any bullet size out there,

Yes, but not with best accuracy and precision. Which is why the 7.62 NATO was designed with a 1:12 twist for the same bullets (150 to 173 grains for combat but used up to 180's for matches) shot in the 30-06 about 100 fps slower from 22" barrels.

30 caliber small cartridges shoot light weight bullets through 1:17 and 1:18 twist barrels winning benchrest matches. World record 100 yard 5-shot .0077" group was made with

http://bulletin.accurateshooter.com/2013/09/best-group-ever-michael-stinnetts-0077-five-shot-group/

 

[IdahoSharpshooter]

A couple thoughts:

The factories abhor reloaders and their experimentation.

Every reloader is a lost customer for factory ammunition. A round of factory ammunition that costs a dollar, is based on a case that costs about 65-cents.

If LAPUA and NORMA did not force the Firearms/Ammunition cartels to sell brass, bullets, powder and primers to consumers (in order not to lose a couple Billion dollars in sales) they would prefer not to.

 

[IdahoSharpshooter]

Factories use the twist rate that best suits the majority of the bullet weight(s) they offer in the rifles they produce.

 

[dkhunt14]

Guys did it ever occur to anyone that a 30 cal Ten twist barrel will shoot just about any bullet size out there, that one of the reasons weatherby changed from a 1-12" to a 1-10 in there 300WBM.
All my 30's are Ten Twist just for that reason!

Joe Salt

Yes, but not with best accuracy and precision. Which is why the 7.62 NATO was designed with a 1:12 twist for the same bullets (150 to 173 grains for combat but used up to 180's for matches) shot in the 30-06 about 100 fps slower from 22" barrels.

30 caliber small cartridges shoot light weight bullets through 1:17 and 1:18 twist barrels winning benchrest matches. World record 100 yard 5-shot .0077" group was made with

http://bulletin.accurateshooter.com/2013/09/best-group-ever-michael-stinnetts-0077-five-shot-group/

First off this thread is about 300 win and long range. That Means big bullets and 10 twist. The 10 twist will handle even the 240 Sierra. The record shot at a mile was shot with a 308 Baer with 240 Sierra bullets. It was a 5 shot group shot at Ohio in an IBS match. The group was right around 7.5 inches. Matt

 

[Joe Salt]

Then why are you talking about 308 Baer? 30 cal win. or 300 WHY same thing a deer won't care about 200 FPS!

Joe Salt

 

[dkhunt14]

Then why are you talking about 308 Baer? 30 cal win. or 300 WHY same thing a deer won't care about 200 FPS!

Joe Salt

Becuase the 308 Baer and 300 win have close to same velocity and capacity. They are both long range 30 cal. and not a short range gun with light bullets. A 10 will handle almost any 30 cal bullet.

It was your gun Smith that shot that group, you should know that. Matt

 

[Joe Salt]

Matt I know that, I was there I helped him get on paper!

Joe Salt