6BR Velicity with 107s

[BoilerBobcat]

For starters, I'm 98% of the time a Palma sling shooter. I had a 6mm barrel and a reamer sitting round for 2 or 3 years, and finally got around to throwing it on a old Savage Palma target action. The barrel is a 30" Bartlein, and not a tight bore or any thing special. I loaded up a few rounds to do an initial barrel break-in, and used 29.8 gr of varget with 107 Sierra MatchKings .015 off the lands, and put them on target at the end of a 1000 yard match one day. It sounded like 30 gr of varget was a pretty standard load, so I backed it down a little. (I know my starting point probably makes people cringe, but like I said, I'm a Palma shooter who typically throws a new Palma 95 308 barrel on, puts 46.2 Gran's of varget in a case with a 155 and goes from there. And Yes...first shot out of the gun was at 1000, and my boresighting procedure got me on paper for a 10.)

I shot 10 rounds, and had a nice 14" group that likely would have been even better as I was reacclimating to the old Savage Accutrigger from my usual Anschutz two stages. I was using a Shotmarker system and it was estimating a speed at the target of 1450fps. Using JBM, that translates to roughly 3020+ at the muzzle!!! While i know that the Shotmarker's velocity estimate isnt perfect, it is usually pretty close when I'm using chronographed (Magnetospeed) loads with my palma 308-155 loads. The 3000+ for the 6 BR seems WAY too fast based on everything else I read about other folks velocities. The cases show no signs of pressure I can detect.... But then again, the 6BR case is fairly new to me, so maybe I'm not seeing something.

Am I in dangerous territory? Should I back way down with varget to get closer to 2900? Should I not believe the Shotmarker/ JBM value, and try my Magnetospeed? I plan to do some more testing and validation, but would appreciate some other folks thoughts who have extensive experience with 6BRs.

Thanks in advance,
Tom

 

[urbanrifleman]

Maybe your BC estimation is off.

 

[oldduc]

For starters, I'm 98% of the time a Palma sling shooter. I had a 6mm barrel and a reamer sitting round for 2 or 3 years, and finally got around to throwing it on a old Savage Palma target action. The barrel is a 30" Bartlein, and not a tight bore or any thing special. I loaded up a few rounds to do an initial barrel break-in, and used 29.8 gr of varget with 107 Sierra MatchKings .015 off the lands, and put them on target at the end of a 1000 yard match one day. It sounded like 30 gr of varget was a pretty standard load, so I backed it down a little. (I know my starting point probably makes people cringe, but like I said, I'm a Palma shooter who typically throws a new Palma 95 308 barrel on, puts 46.2 Gran's of varget in a case with a 155 and goes from there. And Yes...first shot out of the gun was at 1000, and my boresighting procedure got me on paper for a 10.)

I shot 10 rounds, and had a nice 14" group that likely would have been even better as I was reacclimating to the old Savage Accutrigger from my usual Anschutz two stages. I was using a Shotmarker system and it was estimating a speed at the target of 1450fps. Using JBM, that translates to roughly 3020+ at the muzzle!!! While i know that the Shotmarker's velocity estimate isnt perfect, it is usually pretty close when I'm using chronographed (Magnetospeed) loads with my palma 308-155 loads. The 3000+ for the 6 BR seems WAY too fast based on everything else I read about other folks velocities. The cases show no signs of pressure I can detect.... But then again, the 6BR case is fairly new to me, so maybe I'm not seeing something.

Am I in dangerous territory? Should I back way down with varget to get closer to 2900? Should I not believe the Shotmarker/ JBM value, and try my Magnetospeed? I plan to do some more testing and validation, but would appreciate some other folks thoughts who have extensive experience with 6BRs.

Thanks in advance,
Tom

Somethings not right. There's pretty much no way you can get 3020fps in a 6BR with 29.8gr of Varget and a 107SMK.

 

[FrankG]

If I recall correctly fire forming my 6BR cases to 6BRA with that load I was around 2776fps. You lose a little velocity forming the cases but I either way I don't see ya getting 3k+ with a 6BR and the heavy bullets.

My barrel is 26” finish for reference.

Later, Frank
Bartlein Barrels

 

[creedfan]

29.8 of varget out of my 30” 5R gets me 2865 fps with 105gr

 

[KenOath]

My current BR with 30gns Varget, 107 Sierra 30” Barrel is giving me 2811fps.

 

[JFrank]

I run 30.0 gr of Varget behind a 108 Berger average is around 2830 ish 28 inch barrel

 

[BoilerBobcat]

Maybe your BC estimation is off.

I was using the stuff on-file in JBM, and both the Litz BC and the Sierra gave approximately same result.

 

[BoilerBobcat]

Thanks for the sanity check everyone. I'm going to put these across a Magnetospeed and see what the muzzle velocity is. I figured that my target had to be incredibly optimistic on the velocities. I was worried I perhaps had a kaboom waiting in my rifle.

 

[JFrank]

I never check FPS until the load is complete.
I only concern myself with what I see on paper.
J

 

[BoilerBobcat]

As a follow up if anyone is interested, the rounds clocked at 2863 using a Magnetospeed.

Shot a 299-19x on the 300 meter ISSF Target, and called my 9 (and most of the 10's). A score like that makes it hard to want to do any further load development.....

 

[KenOath]

That speed is closer to the average..