What twist for 30BR

R

rputansu

Guest
I am in the planning stages of putting together a 30BR LV and would like to hear what twist and why? What pills to push and popular weights? The usual load data, popular powders and why the choice. This will be my first full out BR rifle and I want to sift through the information so I can make an informed decision. I have several accurate varmint rifles (223, 257Rbts, 6BR, 308) and think it's time to commit to a purebred benchrest rifle.
TIA for the input,
Robert
 
I have found that an 18" twist is great for 110 gr to 125 gr bullets. You can even do fine with the 135 gr. Some may think this is pushing it a bit, but if they ran the test I did, I believe they would agree. I fired a group with the 150 gr Sierra Matchking from a 18.7" twist. I was very surprised to see that they went into .170". I would never push it this far in a match. The same bullet in a 20" twist resulted in tumbling bullets. Stick with the 125 gr and under, because this was from my 30-30, and the velocity of the 150 gr was 2800 fps. The new 115 gr Berger with a dose of H4198SC would be a hard combination to improve on.

Michael
 
17 to 18 Twist, and if this is to be a LV light bullets such as 112 Bibs , 110 Bergers, or 115 Eubers to name a few will be easier on the shoulder. H4198 is your best all around powder choice , N130 is also very popular but more expensive and frequently harder to come by.

Dick
 
If this is your first BR rifle seriously consider not building a 10.5# LV 30BR. I did it and found the recoil was annoying to say the least, a 13.5# 30BR will be easier to learn to shoot well in a shorter time frame.
 
30br

Just like the 6PPC, there is now an entire industry that has cropped up in support of the 30BR.

A typical 30BR rig will have a 1-17 or 1-18 twist barrel, shoot 112 to 125 grn bullets, use N130 or H4198 powder, have a "zero" freebore chamber, and probably be built on a HV platform.

This wheel has been invented, and invented quite well. You mentioned "pure bred Benchrest Rifle", I assume you are going to shoot score. For group, I would still go with a 6PPC.

I agree with MRL in that unless you are going to be competing in a lot of IBS Varmint for Score matches where they do shoot LV in quest for Shooter of the Year Points, build a HV. While many will tell you that a 30BR at 10.5 pounds is no problem, it does pop you pretty hard, especially if you shoot free re-coil.......jackie
 
I wouldn't waste time building a 30BR...Jim Borden has one for sale in the classifieds for $2300...that is a bargain...this rifle is built on the Rimrock BRM action...these rifles he builds shoot 250-25x pretty often and you can have it NOW...
just my 2 cents worth...
 
30 br

Well,
Some sound advice. I'll go with the HV platform and the longer twist of 17 to 18. Getting beat up at the bench isn't appealing. I must admit that I don't quite understand why the 17 or 18 twist shoots better than say a 13 or 14 in the 30 cal. I have a 14 twist 6BR that shoots the light pills very well but why does the 115 grain or so 30 cal pill shoot so well in a 17 or 18 twist? I just can't wrap my mind around it.
Also wondering if anyone has tried Varget in the 30BR. I must admit I have a fondness for Varget because it is so forgiving in many caliber combinations.
Thanks for the replys,
Robert
 
Robert;
Varget is slow for a .30BR. The reason that the .30BR requires a faster powder is the difference in the expansion ratios of the cases when compared to a 6BR. However, you owe it to yourself to try Varget in your rifle when you get it and prove this to your self. The reason for the slow twist barrels is the reduction in torque at load start. I don't see any reason that a .30BR would shoot worse with a 14 twist barrel other than the jumping around in the bags that comes with a faster twist. I saw a .30BR built on a 10 twist barrel when they first came around. The rifle was a bear. I would like to try a Bartlein 22 to 16-17 gain twist barrel with a .30BR. It might be even more calm. We'll see.

Mike Swartz
 
Robert

Varget is on the slow side for the 30BR with the lighter bullets.

The reason shooters use the slower twist is because it is deadly accurate and really tames the Rifle down in the bags, ie, very little torque. You can really tell the difference when going from a 14 or 15 to a 17 or 18.

Randy Robinette of BIB bullets can give the best explanation as to why the faster powders work so well in what is a relativew small case for such a large caliber.

This is one of those instances where a lot of good shooters have already done a tremendous amount of homework geeting this combination to work. Don't be tempted to re-invent this wheel.......jackie
 
Robert, the caliber of the bore and bullet weight determine barrel twist..Most of the super slow twist barrels used today were direct results of trial and error testing NOT from a ballistics chart..Varget is a slow burning powder that requires a specific bore diameter to bullet weight ratio to work properly..
The 30BR has had every powder in the book tested for best fit..and when you hear H4198 or VV N130 is a good fit..then save money and bullets..you won't beat that combination...Your biggest challenge is going to be learning good consistant bench technique behind the 30BR..Buy a bunch of good custom 112-118 grain bullets and a lot of H-4198 and practice with windflags as often as possible..The great thing about a 30BR is one barrel will last 5 times longer than any 6mm ...
I have both 17 and 18 twist rifles, and both shoot equally well...When I beat the 6ppc's in a group match, I can't stop smiling for a week..:D:D
 
Excellant,
I never thought about the resistance, makes perfect sense. I agree with not re-inventing the wheel. I will take the advice and spend the money on good bullets and powder. One of the things that swayed me towards the 30BR is barrel life. I like the idea of building confidence in your equipment and knowing that you'll have it for a while before the accuracy begins to slip.
Robert
 
eww1350 said:
Robert, the caliber of the bore and bullet weight determine barrel twist
Click to expand...

Bullet length, not weight, is the important thing.

eww1350 said:
Most of the super slow twist barrels used today were direct results of trial and error testing NOT from a ballistics chart.
Click to expand...

The 'slow' twist .30 cal. barrels resulted directly from Randy Robinett's work with the JBM Ballistics Drag/Twist Function program. The JBM calculations are based on the works of the late Robert McCoy (McDrag, McGyro, etc.) Randy spoke to this directly in an article I wrote for Precision Shooting several years ago where he detailed the development of the so-called 'slow twist'* barrels and the 30BR cartridge.

* - A 6PPC with a 1:14 twist barrel shooting a 65-68gr. bullet based on a .825 length jacket at around 3,400 fps.(the 'normal' 6PPC combo) has a G.S. (Gyroscopic Stability) figure of around 1.4.
- A 30BR with a 1:18 twist barrel shooting a 118-125gr. bullet based on a 1.00 long jacket at around 3,000 fps. also has a G.S. number of around 1.4.

So...why are the 17-18 twist .30 barrels considered 'slow twist'? :confused: They are no 'slower' with respect to the G.S. number as the thousands of 1:14 barrels that have been chambered for the 6PPC's over the years.:rolleyes:

Even after all the seasons of these .30's being proven competitive, you still get shooters that can't imagine how a 'slow twist' .30 can work....when in fact they're shooting the identical combination on their 6PPCs. ;)
 
jackie schmidt said:
Randy Robinette of BIB bullets can give the best explanation as to why the faster powders work so well in what is a relativew small case for such a large caliber.
Click to expand...

Another attribute is the reduction in muzzle pressure from using these faster powders. The 30BR (and probably the 30PPC as well) have expansion ratios that make some of these faster powders behave quite differently from what most would suspect. -Al
 
I find it interesting

That so many people consider a 30 BR as a high recoiling rifle. Lots of us shoot larger cased 30's in 10 LB rifles with 2.25" forends free recoil all day long. Some of even shoot two of them all day long, without any adverse effects ; as far as we can tell! That considered, a 30 BR in a LV configuration shouldn't be a a big deal, especially if one puts a small Sorbathane pad on it. Heck, you'd never feel it go off, hardly!
 
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30BR will spoil ya!!!!

eww1350 said:
Robert, the caliber of the bore and bullet weight determine barrel twist..Most of the super slow twist barrels used today were direct results of trial and error testing NOT from a ballistics chart..Varget is a slow burning powder that requires a specific bore diameter to bullet weight ratio to work properly..
The 30BR has had every powder in the book tested for best fit..and when you hear H4198 or VV N130 is a good fit..then save money and bullets..you won't beat that combination...Your biggest challenge is going to be learning good consistant bench technique behind the 30BR..Buy a bunch of good custom 112-118 grain bullets and a lot of H-4198 and practice with windflags as often as possible..The great thing about a 30BR is one barrel will last 5 times longer than any 6mm ...
I have both 17 and 18 twist rifles, and both shoot equally well...When I beat the 6ppc's in a group match, I can't stop smiling for a week..:D:D
Click to expand...


Robert......

I promise you that your getting EXCELLENT advice here!

You have chosen a WONDERFUL Benchrest cartridge....

My .02 worth of advice...
The rifle, yes build one that'll weigh 13.5 finished... But one that can be a 10.5 with just barrel/weight system swap.
Bolt face, get a .308 bolt face >>> That will "pick out" a .440 PPC rim<<< as well... ANY of the custom action makers can do this set-up with ease...

Barrel, If a cut barrel Krieger, Bartlein, Rock Creek, Brux... Then you'll get an exact twist rate............... Button rifled Hart, Shilen, PacNor, Broughton, etc ... It may be advisable to go the 17 twist so you know your OK "if" the barrel measures 17 1/2" or 18" twist rate finished.... The button barrels "can" slip in the twist rate a tad... Safe to go one inch faster in the twist rate...

Good news..... The .30 barrels of today are FREAK'N Awesome!!!! I'll bet you'll get a SHOOTER... The SHOOTERS are by far THE NORM!

Bullets.... These to SHOOT.........AMAZINGLY well! BIB'S and Cheeks are outstanding.

Powder............... H4198 <<<< Ohhhhh Yesssss.!
Bet you'll see LOTTSA virtical out of Varget....Way to slow...


Here is the big thing I have learned about the 30BR.... Pretty stout neck tention...Example: I shoot a .334NK and my finished rounds (bullet seated in neck) measure .3323.... I use a .328 bushing to achieve .004 neck tension.
anything less and some degree of virtical you'll get or "fatish" groups....

Good luck on your set-up.... You'll see, Absolute FUN!

More advice will follow in this thread....

cale
 
rputansu said:
Well,
Some sound advice. I'll go with the HV platform and the longer twist of 17 to 18. Getting beat up at the bench isn't appealing. I must admit that I don't quite understand why the 17 or 18 twist shoots better than say a 13 or 14 in the 30 cal. I have a 14 twist 6BR that shoots the light pills very well but why does the 115 grain or so 30 cal pill shoot so well in a 17 or 18 twist? I just can't wrap my mind around it.
Also wondering if anyone has tried Varget in the 30BR. I must admit I have a fondness for Varget because it is so forgiving in many caliber combinations.
Thanks for the replys,
Robert
Click to expand...


Maybe I missed it but I haven't seen this mentioned.

You ask this question, "but why does the 115 grain or so 30 cal pill shoot so well in a 17 or 18 twist? I just can't wrap my mind around it."

Here's one reason that will make sense.


One of the biggest contributors to dispersion on the target (group size) is something called "bullet eccentricity", the fact that no bullet is PERFECTLY balanced means that they all wobble some, their center of rotation isn't perfectly matched to center of form.......... in other words they're heavier on one side.

The slower you spin a bullet the better for accuracy, AS LONG AS you don't sacrifice stability.

If you were to shoot the same bullet from an 18" twist and a 10" twist barrel then it follows that the bullet which is wobbling LESS will show less dispersion (tighter groups) This is a wonderful thing :) with the thirty-cal's you get very well balanced bullets, a setup that's as inherently accurate as the 6BR, a setup that's just as stable ballistically as the 6BR, AND the added bonus of a slower rotation on your projectile......... it's a win-win.


Except for the recoil.



Now, to diverge a little.

Let me point out that if you run that BR reamer in a little deeper and use the 30X47 for your chambering you will not only be able to make just as good a shooter, but you'll also have a legal HBR gun. You could conceivably shoot this same gun for Group, Score AND Hunter Bench Rest. THIS would make it a purebred BR rifle. I'd put it together to make 10lb with a 6X scope and with a weight system to bring it up to 13.5 when you want to. I'd furthermore make a 3" wide removable plate for the forend for score and group shooting...... I have one of these setups and with it can compete in literally any venue.


If you can handle the recoil.

I can't see a downside to the 30X47 based on the new 6.5X47L case.

UN-believably accurate.

UN-believably wide tuning windows.

BTW the Borden is a good deal.


al
 
alinwa said:
One of the biggest contributors to dispersion on the target (group size) is something called "bullet eccentricity", the fact that no bullet is PERFECTLY balanced means that they all wobble some, their center of rotation isn't perfectly matched to center of form.......... in other words they're heavier on one side.

The slower you spin a bullet the better for accuracy, AS LONG AS you don't sacrifice stability.

If you were to shoot the same bullet from an 18" twist and a 10" twist barrel then it follows that the bullet which is wobbling LESS will show less dispersion (tighter groups) This is a wonderful thing :) with the thirty-cal's you get very well balanced bullets, a setup that's as inherently accurate as the 6BR, a setup that's just as stable ballistically as the 6BR, AND the added bonus of a slower rotation on your projectile......... it's a win-win.al
Click to expand...

alinwa: Let's take this a bit further.

-You have 6mm and .30 cal. jackets.
-Both have a T.I.R. of .0002.

Which has the potential to produce a better bullet? Think 'circumference'. :)
 
A little off subject, but

Most people on here have realized the accuracy advantages of using as slow a twist as you can get by with and still stabilize the bullet. Here is another big advantage. Let's take a 150 gr bullet at 3200 fps and you will have a bullet rpm of 230400. Now the same bullet out of a 16" twist will have an rpm of 144000. That's 86400 lets rpm. This drastically changes the bullets ability to penetrate to the vitals of game. So you hunters need to try this. I was actually a little disapointed in how the Ballistic Tips don't expand as much on neck shots on deer. It used to bore a 3" hole through the neck with a 10" twist, but with a 16" twist it's more like 1.5" hole. Now rather than using 180-200 gr bullets with a 10" twist in my 30-338 Win Mag for Elk hunting, I will be using 150 gr pills and a 16" twist with equal penetration.

Michael
 
Alinwa brings up a curious point with the 30X47. This seems to be a versatile cartridge but how much of a hastle would it be to switch from group, score and HBR? Money always seems to be an issue so I will most likely stick to single purpose rifle for a while. I will have to take a look at the 6.5X47 and compare it to the BR case.
Is there an advantage of 30X47 over the 30BR?
Robert
 
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