6BR and 6BRA velocities (90gr Berger)

[gcabrera]

Last weekend @6BRA and me had a very productive tuning session. He was tuning his 6BRA and I was tuning my 6BR, both using the 90gr Berger bullets and H4895 powder. Lapua brass on both as well.
Mike's gun has a Bartlein 1:8" twist, and mine has a Krieger 1:10".
Ambient temperature in the 35°F-40°F.

Mike had the new Garmin chrono attached to its rest, gosh I need one of those!
He actually helped getting me back in tune, as my velocities had fallen well below my tuning window.
I can safely say that having the Garmin handy actually saved the day.

With that data available, wanted to share it to contribute to the community 'knowledge bank' of these two popular cartridges.

On the X axis is muzzle velocities, and on the Y axis are the # of shots recorded during the tuning session at that velocity:


Please do not extract any conclusions about SD or ES from this data set, as we were tuning and sweeping charges from very light to the very top.
My 6BR max'd out at 3200fps, while Mike's 6BRA max'd at 3330fps.

Both guns showed a pretty wide accuracy window near the top.
The 6BR printed nicely at 3170fps, while the 6BRA did the same at 3270fps.

Keep it handy in case you ever venture this route.

 

[Kevin1990]

What are your barrel lengths, out of curiosity?

 

[marchx]

I run the numbers and in 28" barrel 3170fps you can get with 31.5gr of H4895.
My guess is 28" barrel.
Interesting- I did modelling for 105s- I can get 100fps more with H4895 than with VVN140 before achieving pmax.

 

[6BRA]

What are your barrel lengths, out of curiosity?

the Bra was a 30".

 

[gcabrera]

Yes, the 6BR has a 25” long barrel.

 

[Kevin1990]

Yes, the 6BR has a 25” long barrel.

That’s good to hear. I have a 24” 6br coming, and was wondering what ball park velocities people were getting with the 90bt but couldn’t find much. Not to derail the original post. But how’d dis they group?

 

[gcabrera]

That’s good to hear. I have a 24” 6br coming, and was wondering what ball park velocities people were getting with the 90bt but couldn’t find much. Not to derail the original post. But how’d dis they group?

We were mainly focused on vertical and how they bucked the wind.
The best groups we had were in the 0.5” with about one bullet hole of vertical.
Many other groups we’d better not talk about

 

[gcabrera]

At 200 yards.