6BRX Twist Rate Help

[AWLEAPHART]

Ok everyone,
Im need so help here.
I have a 6BRX with a long free bore and a 1 in 8.4 twist. Don't ask I have no clue of why it's not an 1 in 8. I have checked it over and over and it's a 1 in 8.4.
So what I have read is that the 105's do best with 1:8 twist. So I'm thinking of trying the 95 grain Bergers and seated out to the lands I'm only getting 0.10 of the bullet in the case And yes that is starting at the heal is what I think they call it. Does anyone see a problem with that and has anyone been getting better results with a jump instead of touching the lands. With the 95G Im not going to try a jam with only .10 in the case.
Has anyone tried 105 with a 8.4 twist?
Thanks Anthony

 

[Dubya]

Ok everyone,
Im need so help here.
I have a 6BRX with a long free bore and a 1 in 8.4 twist. Don't ask I have no clue of why it's not an 1 in 8. I have checked it over and over and it's a 1 in 8.4.
So what I have read is that the 105's do best with 1:8 twist. So I'm thinking of trying the 95 grain Bergers and seated out to the lands I'm only getting 0.10 of the bullet in the case And yes that is starting at the heal is what I think they call it. Does anyone see a problem with that and has anyone been getting better results with a jump instead of touching the lands. With the 95G Im not going to try a jam with only .10 in the case.
Has anyone tried 105 with a 8.4 twist?
Thanks Anthony

Yes! had a 8.7 to 8.3 twist that shot 105-107 bullets. Worked just fine.

 

[Sheldon N]

Twist isn't a thing where it's "stable" vs "unstable". There's a big grey area where you may have stability to keep the bullet flying straight, but you sacrifice a little bit of BC potential. The extent to which you are compromised is not just determined by the twist rate, but also by velocity and the environmental conditions you are shooting in. You can check those out and get more detail at the Berger twist rate stability calculator.

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

From a gut level reaction I would say stick with the 105's. Even with a slightly compromised BC they will likely outperform the 95's.

 

[AWLEAPHART]

So I take it that you losing BC but will still shoot good groups?
I have a box of 105 hybrids and a box of 95G I can try.
Bergers web page has my SD at 1.35 with 105 hybrids and 1.68 S.D with the 95G. So at 600 yards I guess the 105 are taking a chance but the 95 are a good to go?

 

[Sheldon N]

I guess the 105 are taking a chance but the 95 are a good to go?

A 1.35 SG is a 4% reduction in BC. So the Berger 105 Hybrids would have a net G7 BC of around 0.264. The Berger 95 VLD would have a G7 BC of 0.240. So the 105 will still be more resistant to variable winds than the 95, even though the 105 is not fully stabilized.

 

[rocketron]

So I take it that you losing BC but will still shoot good groups?
I have a box of 105 hybrids and a box of 95G I can try.
Bergers web page has my SD at 1.35 with 105 hybrids and 1.68 S.D with the 95G. So at 600 yards I guess the 105 are taking a chance but the 95 are a good to go?

Run the numbers for the 105 vld and the 108. I've had better luck with these than the 105 hyb in my 8 twist brx.

 

[Grimstod]

I would give the 6mm 105gr VLD Target a try. That bullet is slightly shorter then the 105gr Hybrid and does not require as fast a twist. You will get some more stability, gain some BC over the 95gr and wont loose any stability.

I have a 6BRX and if I run the numbers with your twist rate it gets these SG results.

108gr BT Match
SG = 1.48Bullet BC (G7): 0.268Adjusted BC for 1 in 8.4" Twist:0.266Your BC is being compromised by: 1%Minimum Twist Recommended: 1 in 8.25"

105gr VLD Match
SG = 1.44Bullet BC (G7): 0.265Adjusted BC for 1 in 8.4" Twist:0.260Your BC is being compromised by: 2%Minimum Twist Recommended: 1 in 8.00"

105gr VLD Hybrid
SG = 1.31Bullet BC (G7): 0.275Adjusted BC for 1 in 8.4" Twist:0.259Your BC is being compromised by: 6%Minimum Twist Recommended: 1 in 7.75"

Since you have a long freebore I think you will get the best results with a 108gr.
Hope this helps.

 

[tclaunch]

I would give the 6mm 105gr VLD Target a try. That bullet is slightly shorter then the 105gr Hybrid and does not require as fast a twist. You will get some more stability, gain some BC over the 95gr and wont loose any stability.

I have a 6BRX and if I run the numbers with your twist rate it gets these SG results.

108gr BT Match
SG = 1.48Bullet BC (G7): 0.268Adjusted BC for 1 in 8.4" Twist:0.266Your BC is being compromised by: 1%Minimum Twist Recommended: 1 in 8.25"

105gr VLD Match
SG = 1.44Bullet BC (G7): 0.265Adjusted BC for 1 in 8.4" Twist:0.260Your BC is being compromised by: 2%Minimum Twist Recommended: 1 in 8.00"

105gr VLD Hybrid
SG = 1.31Bullet BC (G7): 0.275Adjusted BC for 1 in 8.4" Twist:0.259Your BC is being compromised by: 6%Minimum Twist Recommended: 1 in 7.75"

Since you have a long freebore I think you will get the best results with a 108gr.
Hope this helps.

Great advise.

 

[AWLEAPHART]

Thanks guys for the advice.
Anthony

 

[Cool Tool]

Thanks guys for the advice.
Anthony

Sir in the beginning of your post you said that your barrel in question was supposed to be a 8 twist an after testing with what ever method of testing you came up with 8.4 my question is was the barrel marked 8 twist.

 

[mikecr]

A good amount of this depends on the shooting air density.
OP's profile suggests SC, which is likely lower in altitude, but warm and always high in relative humidity.
For others it's different.

 

[Yote Hunter]

I wouldn't rule out the 95 gr Berger VLD. Leonard Baity, a well respected gunsmith for 1000 yard rifles, told me that he discovered the 8.4 twist was ideal for that bullet. He was using them to fire form and discovered that was the best bullet by accident. Outperformed the 105 class and the additional speed gained may be a toss up as to which bullet truly has the advantage in the wind.

 

[500Stroker]

I shot 108 Bergers in my BRX and they rock. My barrel is an 8 twist with a .140 freebore

 

[Bob L.]

Run the numbers for the 105 vld and the 108. I've had better luck with these than the 105 hyb in my 8 twist brx.

This has been my experience as well.

 

[RonAKA]

Ok everyone,
Im need so help here.
I have a 6BRX with a long free bore and a 1 in 8.4 twist. Don't ask I have no clue of why it's not an 1 in 8. I have checked it over and over and it's a 1 in 8.4.
So what I have read is that the 105's do best with 1:8 twist. So I'm thinking of trying the 95 grain Bergers and seated out to the lands I'm only getting 0.10 of the bullet in the case And yes that is starting at the heal is what I think they call it. Does anyone see a problem with that and has anyone been getting better results with a jump instead of touching the lands. With the 95G Im not going to try a jam with only .10 in the case.
Has anyone tried 105 with a 8.4 twist?

I would not give up on the Berger 105 Grain Hybrid without giving it a try, depending on your specifics. I has the highest form factor for the 6mm target bullets. It is going to give you nearly 0.1" extra length to work with your long throat over the 95 grain, and the Hybrid is less sensitive to seating depth. I know that Berger says it needs a 7 twist, but if you enter the specifics for this cartridge and assume 1000 feet and 70 deg, it comes out with a SG of 1.39. The adjusted down G7 is .265. Then if you run the calculator for the 105 VLD it comes out at an SG of 1.53 but still the same 0.265 G7. Downrange performance is going to be close to identical, but you are working with a longer bullet that may fit your throat better...

 

[AWLEAPHART]

Thanks for the replies.
If you get great groups at 100 yards while load testing does that mean a bullet will be stable at 600 yards?
Anthony

 

[savagedasher]

I wouldn't get a new barrel that wasn't faster then a 8 .7.7 or 7.5 would be my choices Larry

 

[LRPV]

Thanks for the replies.
If you get great groups at 100 yards while load testing does that mean a bullet will be stable at 600 yards?
Anthony

In my experience if the twist is too slow the bullets tumble right away. If you have round holes at 100, the bullet stabilized.

 

[RonAKA]

Thanks for the replies.
If you get great groups at 100 yards while load testing does that mean a bullet will be stable at 600 yards?
Anthony

I believe the theory is that forward velocity reduces faster than spin velocity. So, you essentially have more spin and stabilization the further down range you go, as long as it is stable out of the muzzle. Now what happens to it when it gets close to being subsonic is another matter...

 

[AWLEAPHART]

update.
I tried the 105 Hybrids and the 95 VLD's. As of right now the 95 VLD's are doing good. Last 5 shot group was a little under 1/4".
25 thousands into the lands and 33.2G of RL15.
Does anybody have some advice on how to get a one hole
I was around 33.5G but 33.2 seams to be bring it together. I wondering if I should try more into the lands or 33G of RL. I see no pressure signs but I can tell the rifles kick has settle down some at 33.2 vs 33.5.
Thanks Anthony