Rethinking twist, bullets, and freebore--need help

[Badbob]

Folks, I followed my Dad's lead on building up a 6mmbr. Here are the details:

R700 trued action
Criterion Heavy Varmint 6mm barrel 1:10
Custom reamer--.265" neck and .0197" freebore/lead

We initial did load development with 67gr FB Fowler bullets and some decent results. I shot a .197, .238, and .277 3 shot groups. But then later shooting did noting better than .3's.

Having a look at the Berger Twist rate calculator I see that 1:10 is too fast for such a light bullet.

Do you agree? Should I shoot FB 90's? If so, do I have enough freebore? Should I consider rechambering the barrel with longer freebore to manage the longer VLDs?

Any help or suggestions would be great! thanks BB

 

[retired]

not quite sure why you picked a 1/10 and lite bullets ?
what are the plans for the gun ?

 

[357Mag]

Badbob -

Howdy !

FWIW -
Berger's website includes a note about use of the " stability calculator " w/ FB bullets.
It uses the " Miller " formula, which works best w/ BT bullets; according to the website.

http://www.bergerbullets.com/twist-rate-calculator/


With regards,
357Mag

 

[Badbob]

not quite sure why you picked a 1/10 and lite bullets ?
what are the plans for the gun ?

PDogs mostly--but it was to be my first introduction into custom high performing guns and benchrest accuracy. Does that help?

 

[Badbob]

Badbob -

Howdy !

FWIW -
Berger's website includes a note about use of the " stability calculator " w/ FB bullets.
It uses the " Miller " formula, which works best w/ BT bullets; according to the website.

http://www.bergerbullets.com/twist-rate-calculator/


With regards,
357Mag

I saw that note . . . do you think I should switch off of FB bullets and shoot the 65-70gr BTs?

 

[retired]

i would buy a box of 74 sierra or similar and try those.

PDogs mostly--but it was to be my first introduction into custom high performing guns and benchrest accuracy. Does that help?

 

[urbanrifleman]

Sierra 80 Blitz or 80 Berger. You can also shoot the Berger 90 VLD.

 

[urbanrifleman]

It is not "too fast". I think you are reading "suggested" and making some assumption about performance. I shoot a lot light bullets with the 8 twist and its a lot of fun. Heck, try to find a slow twist barrel these days!!!

 

[tuttlefarm]

Try the 87 V-max.............

 

[Badbob]

It is not "too fast". I think you are reading "suggested" and making some assumption about performance. I shoot a lot light bullets with the 8 twist and its a lot of fun. Heck, try to find a slow twist barrel these days!!!

Ok, thanks! Can you be more specific? What pill with your 1:8 twist? How long is your barrel and what kind of results have you been getting. That would be helpful.

Anybody else have good results with a 1:8 to 1:10 in the 60 gr range? Thanks BB

 

[geraldgee]

My 6BR favors the Berger 87gr VLDS. I built with a 9twt thinking 90gr Lapuas. I bought 500 of the Scenars - it likes the Bergers so well it may be awhile before I get to the Scenars.

Good luck.

Gerald

EDIT: Taken from the 6BR Cartridge Guide on the A/S homepage,
"For medium range or 1:10 twist barrels: Berger 88gr Low Drag FB, BIB 95gr FB, or Hornady 87-gr V-Max. The BIB is superbly accurate, having shot sub .2″ groups at 200 yards."

The bullets you try will determine if they like the twist or not - all else is academic.

 

[JRS]

The ideal twist for the 67GR FB would be 1:13.5"

 

[urbanrifleman]

Ok, thanks! Can you be more specific? What pill with your 1:8 twist? How long is your barrel and what kind of results have you been getting. That would be helpful.

Anybody else have good results with a 1:8 to 1:10 in the 60 gr range? Thanks BB

If you get a 1-8 twist with a .100 FB 6BR, you can shoot 108-70 grain bullets quite accurately and all the bullets can be seated to the lands. I like the 108 Berger and 30 grains R15 for long range.

You can shoot the 1-8 with the 80 grain Bergers and Sierra Blitz into tiny little bugholes. I use R10x at 28.5 with CCI 450s and Lapua Brass jumping .020. R15 is good too as is Varget.

The 70 Sierrra HP is also quite good as is the 70 TNT. Of course there are tons and tons of 68s made for benchrest competition. All of those are good.

 

[Greyfox]

I'm going to go in a different direction here. You don't mention what kind of scope and bench setup you are using. Also, you don't mention wind flags. Now maybe you have everything you need, but if you aren't using a fairly high magnification scope and some kind of wind indicator, you are going to have trouble shooting consistent groups lower than a .3. I know all the keyboard shooters here claim their rifle will shoot .250 "all day long", but in truth, that's mostly dreaming or BS. In fact, plenty of the pics that are shown prove that many don't even know how to measure groups.
You shouldn't have trouble getting consistently good groups with light bullets in that twist. It when you go the other way that you have problems. I've shot thousands of 40gr bullets in 223 AIs with a 1-9 twist and never had an issue. I seriously dou7bt you will have a problem with your 1-110 using light bullets. All that being said, most people really like that Hornady 87gr.

Rick

 

[Toby Bradshaw]

In fact, plenty of the pics that are shown prove that many don't even know how to measure groups.

Been biting my tongue on that, but somebody had to say it.

 

[Badbob]

I'm going to go in a different direction here. You don't mention what kind of scope and bench setup you are using. Also, you don't mention wind flags. Now maybe you have everything you need, but if you aren't using a fairly high magnification scope and some kind of wind indicator, you are going to have trouble shooting consistent groups lower than a .3. I know all the keyboard shooters here claim their rifle will shoot .250 "all day long", but in truth, that's mostly dreaming or BS. In fact, plenty of the pics that are shown prove that many don't even know how to measure groups.
You shouldn't have trouble getting consistently good groups with light bullets in that twist. It when you go the other way that you have problems. I've shot thousands of 40gr bullets in 223 AIs with a 1-9 twist and never had an issue. I seriously dou7bt you will have a problem with your 1-110 using light bullets. All that being said, most people really like that Hornady 87gr.

Rick

Ya, I gotcha, how my ability plays into the whole equation is a big unknown. In fact, that can be very frustrating when you are trying to figure out if it is the gun, the load, or just you!

Perhaps this will help.
Windflags=yes
Sightron 8-32x in Burris Rings
Bald Eagle rest and bags
Laminated stock with 2.25" flat forearm.

On my 6x47 I've only been able to shoot .3xx, but I'm in the midst of load developement.

Thanks for the honest input.

 

[Badbob]

Been biting my tongue on that, but somebody had to say it.

Center to center from the the two shots that are the farthest apart. Actually I find it easier to measure outside to inside with calipers. I've used OnTarget to double check my measuring and the program is more generous. But we are pretty close.

Honestly, I'm not into sandbagging my shooting. I really want to improve my shooting, my loading, and hardware.

Thanks BB