6mm BR w/ 1 in 9" twist - max pill weight

[dangaff]

Hi guys,
I'm new here, ill give you bit of a background behind my 6mm BR.

I already own a Manners T2 inletted for the Savage Model 12 VLP.
Once i buy the VLP (243W) early december probably ill take it to get a rebarrel.

I spoke with the bloke before and due to the VLP coming in a 1 in 9.25" twist, that's basically what my 6BR will end up us.

What are the maximum pills ill be able to handle with this twist and also the lightest?

He also mentioned he will need to do bit of a rechamber, his was mentioning making it a short-neck throat chamber, he said it just means ill lose a bit of velocity and the bullet will be seated deeper.

I can't wait for this build!!
I also ordered a Forster benchrest seater & neck sizer, aswell as a forster full length sizer separately.
I have the opportunity of buying 300, 105grn VLD's aswell as 100, 108grn VLD's.
Should i just get the 105's?

Cheers guys
Dan

 

[TheBlueEyedBear]

According to the BERGER Bullets website the requuired twist rate is 1-8. You might want to try the 80-95gr. bullets in this barrel.
http://www.bergerbullets.com/Products/Target%20Bullets.html

 

[Kenny474]

Couple questions for you about the build.
First, if you are going to rebarrel the rifle, why do you need to use a 1-9? Why can you not use a 1-8 twist so you can shoot heavier bullets? Unless the smith plans to rechamber the .243 barrel to 6BR, which I feel is a bad idea and a waste of time and money anyway, why can he not order you a 1-8 barrel?

Does this smith have any experience with the 6BR? Or does he only have a reamer throated for light bullets and won't get you a proper reamer for the longer bullets?

You can order a pre-chambered barrel which will be set-up for the bullets of your choice, and install it yourself with only a few special tools, and likely save money and have better results than if the smith cuts your chamber too short anyway.

A too short chamber will give you issues with neck/shoulder junction donuts, will reduce case capacity as the bullet will be too far into the case, cost you velocity and is just not at all ideal for your planned build.

Unless you go with a 1-8 barrel, you will be shooting 95gr Bergers or lighter/shorter bullets, as the 1-9" will not stabilize a 105 VLD, just not going to happen.

I think you need a new smith, or at least a new plan of attack. You will be much happier with a 1-8 twist barrel, preferably a custom barrel as well.

 

[Gman]

If you keep the velocity above 2800 fps, I believe that a "true" 1 in 9" twist will stabilize the 6mm Hornady 105 gr A-Max, but finding any quantity of them is like finding hens teeth. It also might stabilize the 6mm Berger 105 gr BT's, but you will have to try both bullets in YOUR bbl to see if they will fly true.

 

[dangaff]

Hi guys,

Thanks for the information.

I think ill just go with a 1 in 8" twist shilen pre-fit.
Cost a bit extra but i've already bought the 105's so may aswell.
More versatile twist rate too.

Now just weighing up whether to stevens or savage

 

[Kenny474]

For a donor rifle on which the stock and barrel will be replaced, Steven's all the way. They are the same exact action as the pre-accu-trigger Savage.

Add a Rifle Basix SAV-2 trigger, or one of the SSS units, and you will have a better trigger than the Accu-trigger anyway.

The Steven's will cost a lot less, and you likely won't use most of the parts you will pay extra for on the Savage anyway.

 

[RonAKA]

You could go with the Savage target action only, if it will fit your stock. It is a very heavy action with a small port (right bolt, left port is my choice). I was at first a little disappointed in the Target AccuTrigger. It was failing to fire way too often. I've done a bit of work on it -- mainly just cleaned it up, and used dry graphite lube. It now pulls at 7 oz., and I've gone 80 straight rounds since the tune up with no fail to fires. You may also want to check out Pac-Nor as they do prefits for the Savage too. What you really need to do though is nail them down on the reamer dimension they will use to be sure it has the right length throat for your bullets of choice, and the neck diameter is suitable for a no turn neck, if that is the way you wish to go. Probably need about .270 with the new blue box Lapua. I would have the brass in my hand and loaded with your bullets so you can measure the neck, and confirm your desired neck size.

The other option of course is simply buy a complete Savage rifle with the heavy barrel and target action. Not sure who makes the barrels for Savage, but mine at least seems very resistant to copper fouling, and produces decent groups.

http://www.savagearms.com/firearms/actions/target/

 

[Kenny474]

RonAKA, Savage make their own button rifled barrels in house.

 

[RonAKA]

RonAKA, Savage make their own button rifled barrels in house.

OK. I had a vague recollection that they had outsourced their barrels from somebody like Douglas, and they are not hand lapped. In any case it makes sense that they make their own, as they must have a high demand for them. I may have confused the issue with Sharp Shooter Supply as I know they sell Douglas barrels prefit for the Savage. In any case I've been impressed with the way mine cleaned up. Somewhere around 30 rounds through it, it stopped showing any copper. Now I can shoot 50 rounds or so, and basically only see carbon when cleaning. Takes about 4 patches to clean.

 

[762willdo]

If you keep the velocity above 2800 fps, I believe that a "true" 1 in 9" twist will stabilize the 6mm Hornady 105 gr A-Max, but finding any quantity of them is like finding hens teeth. It also might stabilize the 6mm Berger 105 gr BT's, but you will have to try both bullets in YOUR bbl to see if they will fly true.

I've tried both of them in a 6 Dasher with a Bartlein 9 twist as well as the Berger 100 grain BT at 3,000+ fps and none came close to working. We're talking a three foot group at 100 yards with most of them sideways. If they stabilize in his barrel, it ain't a 9 twist.

Also, it sounds like maybe he's just gonna' rechamber the 9.25 barrel and I can assure that won't work with any of the above bullets unless Savage had a really bad day.

Stabilization has nothing to do with speed and everything to do with twist and oal of the bullet.

 

[DCRYDER]

Gonna have to disagree with you WILLDO, velocity definately plays a part in stability. According to stability calculator a 6mm bullet with OAL of 1.410" at 3000fps needs at least a 1-8" twist. Same bullet at 3800fps will stabilize in a 1-9" twist. Its a RPM thing. Yes OAL plays a bigger part, but to say speed has nothing to do with it is wrong.

This is why fellows that shoot .308" 240gr bullets subsonic in suppressors need barrels with a 1-7" twist instead of 1-9" or 10" for normal 2500+fps rounds.

 

[dangaff]

The shilen pre-fit im getting, im told its a no-turn neck.

I won't need to adjust any die bushings or neck turn any brass, or will i?

 

[queen_stick]

The timing on this works to your favor...

http://bulletin.accurateshooter.com/2010/11/berger-introduces-new-87gr-6mm-vld-for-110-twist-barrels/

try the 87gr VLD's... they'll probably hammer in that 9.25twist barrel...


As far as a no-turn neck... just load and shoot - no prep work required for fitment. I have a no-turn 6br (.272 neck). I chamfered the insides of the necks for the first firing, then cleaned, trimmed all to the same length, then re-chamfered the insides of the necks. That's all I did, and haven't had any problems over 5 reloads so far. (Won a couple relays at 1K matches over the summer, and that's literally all the prep work I did.)

Also, if you're using Lapua brass, the new lots have smaller neck wall thickness... that may decrease the chamber neck dimension that is considered a "no-turn." For example, the .272 neck is a very popular no-turn, but with new Lapua brass, a .270 or .271 may be more desirable...

 

[Kenny474]

Stabilization has nothing to do with speed and everything to do with twist and oal of the bullet

Sorry to disagree but that's incorrect. Even the original Greenhill formula developed over 130 years ago took muzzle velocity into consideration.

I suggest for your edification you go to the JBM Ballistics website. There you can read about the Miller Stability Factor developed by Don Miller several years ago. There's also a free online calculator you can use to see just how much difference changes in velocity make. You'll also find that barometric pressure, temperature and specific gravity of the projectile are also part of the equation.

http://www.jbmballistics.com/ballistics/calculators/calculators.shtml

+1 The JBM site is very helpful and the stability calculator has worked very well in the past for me. 99% of the time, if it says the bullet won't stabilize, I can't get it to shoot for beans and will usually key-hole or just not group at all.

 

[RonAKA]

Required spin can be difficult to nail down. Berger gives the spin required for their bullets, independent of muzzle velocity. Muzzle velocity does increase stability, but within the typical range of velocities for a given bullet it is not a big effect. The Miller formula is good, but I suspect quite conservative for flat base bullets. I've worked out the stability factor for a number of Berger bullets based on their minimum recommended twist. The stability factor comes out at 1.4 for the VLD profile bullets showing excellent agreement with the Miller rule, and only 1.1 for the flat base bullets. So obviously Berger does not believe the Miller formula works for flat base and are going with a more aggressive method.

Another good source of guidance on spin required is Border Barrels website. Link below. They use the McGyro computer model, which considers bullet shape and bullet density. The Miller rule does not consider either.

The McGyro tool is interesting to play with, and generates a graph of required twist vs muzzle velocity. The only down side of it is that stability is fixed at 1.5, which is a bit on the high side to be ideal. 1.4 would have been better, or better still just allowed you to enter the stability.

http://www.border-barrels.com/barrel_twist.htm

 

[762willdo]

How come 185grn .45cal bullets out of my 1911 aren't sideways when they go through the paper at 75ft???? or even 50yds?????

 

[Kenny474]

How come 185grn .45cal bullets out of my 1911 aren't sideways when they go through the paper at 75ft???? or even 50yds?????

Because they are short and fat and require a slow twist to stabilize at the velocity they are traveling.

Velocity does play a part in stability, as it is one of the determining factors in the RPM of the bullet.

The RPM required for stability depends on the length, diameter and weight of the bullet and also how fast it will be traveling.

Think about it like this, a bullet going 1200fps will spin much slower(lower RPM) in a 1-14 than it would if it were traveling at 4000fps.

 

[DCRYDER]

A 200gr Hornady XTP .452 bullet is 0.567" OAL. According to calculator this bullet with MV of 1000fps only requires 1-40" twist.

If you could push that bullet to 2000fps you would only need 1-56.5" twist barrel.

 

[Gman]

If you keep the velocity above 2800 fps, I believe that a "true" 1 in 9" twist will stabilize the 6mm Hornady 105 gr A-Max, but finding any quantity of them is like finding hens teeth. It also might stabilize the 6mm Berger 105 gr BT's, but you will have to try both bullets in YOUR bbl to see if they will fly true.

I've tried both of them in a 6 Dasher with a Bartlein 9 twist as well as the Berger 100 grain BT at 3,000+ fps and none came close to working. We're talking a three foot group at 100 yards with most of them sideways. If they stabilize in his barrel, it ain't a 9 twist.

Also, it sounds like maybe he's just gonna' rechamber the 9.25 barrel and I can assure that won't work with any of the above bullets unless Savage had a really bad day.

I am not denying your experience, but I have a Rock Creek, 1 in 9" twist, that I will be trying with 105 gr A-Max's (6mm) It is printed on the Hornady box, "requires a 1 in 9" twist", so I figure that I'll give her a try.