7.5 twist for a 6mmbr

[shooter65]

Is it too fast?

Are the 115's too heavy for the 6mmbr?

 

[bughole]

Yes and No it will work but if you want to drive the 115 the 6x47 would be the choice in my book.....The 6BR is awsome in a 10 twist at best but i prefer the 12 twist and the 75 grainers for vermon out to around 600 then the 6x47 with the 108s take over

 

[Steve Blair]

I have also considered a 7.5 for 6BR. It looks like 2800-2900 is achievable in a 30" barrel with RL17 and 115 Bergers. That is my choice powder with 107 Sierras in 6BR. All referenced bullets are moly coated.

At 2800 fps, the 115 Berger is stable and deflects about the same as the Sierra 107 at 3000. It may not be the best choice at 1000 yards but should be a fine 600 yard load.

The obvious question is: If you are only obtaining the same wind results with the 115 and the 107, why shoot the 115?

 

[shooter65]

Will the 8 twist stabilize the 107 and 108's ok?

 

[Steve Blair]

Yes. I shoot a 30", 8" twist 6BR and obtain excellent results using Sierra 107s and RL17. Of course, I use Lapua brass. The rifle shoots down to 1/4 MOA if I don't screw it up.

I have also tried the Berger 105 & 108 and the Hornady A-Max 105. All shot well, but the Sierra worked best in my rifle. YMMV

 

[shooter65]

I use the 105 Bergers with 30.5 of Varget out of a26'' 8 twist.

 

[Steve Blair]

That setup is just fine for 105-108 bullets. Yours is a classic accuracy load for 6BR and should provide somewhere around 2800-2850 in 26".

 

[shooter65]

2880 is what I am getting.

 

[norpacmiami]

My experience with the 6BR has been wide, having used 1/8", and 1/7.5" twist barrels. I have used bullets from as light as 88 gr Berger FB up to the 115 gr Berger VLD.

Having said that, the reamer used has a longer than usual throat, allowing a longer seating of the bullet, and therefore accepting a smithen more powder, without disturbing the pressure monster.

Accuracy at 1,000 yds is excellent, at a speed borthering 2,900 fps. The Sierra 107s and Lapua 105s will do 2,950 fps. I could have gone for the BRX instead, but decided to play with the reamer, and not have to deal with additional dies, brass, necks, etc. It worked.

Barrels with 1/7" are theoreticaly best handling 115 VLDs. I agree and not. Yes, they do fly amazingly well, and they will also occasionaly dissapear when pushed at maximum revolutions. The 1/7.5 seems to do a better job at keeping things in check.

I have also tested this with several 6CM barrels, and the 1/7" will always surprise me (at the worst moment) with a "did not arrive" notice. Not good. The 1/7.5 has proven better so far. Reducing the speed in the 1/7 " barrel helped a lot, but killed the intention.

More to come,

Andy,

 

[HPMike800]

Andy,
For the 6BR with 105-108's, is the accuracy and speed about the same out of a 1/7.5" and a 1/8"?
Mike

 

[norpacmiami]

In my case Mike, yes.