6BR load out to 1K

[Aussie Denis]

Hi guys and gals,

I have a factory Savage 12 F-class 6BR in 1:8 twist.

I shot my 6BR today at 800y(first time), 900y, and 1,000y for the 2nd time ever. First time on this slightly reduced load. The wind was a uniform 3:00 through the morning.

My current load is Lapua brass, 30.3g of AR2208 (Varget), CCI450, pointed Berger 105g VLD's, .005" jammed and .001" neck tension. The load is approximately running at 2850fps.

I was fairly happy with my 800y shoot. It was very consistant (54.2) and I should be able to hit 60's with a little more LR experience. At 900 it was a little less consistant and at 1000y a little less consistant again.

I suspect that the above load is getting close to transonic and de-stabilising after 800y. I think to shoot a 6BR tight at 1K a hotter load is required.

My question to those that have shot 6BR at 1000y:-
How hot have you had to take this load?
Does it sound like I'm on the right track or more likely over analysing?

Thanks, Denis.

 

[Bert]

Give the 105 hybrid a try they carry well to a 1000 in the BR

 

[Laurie]

I suspect that the above load is getting close to transonic and de-stabilising after 800y. I think to shoot a 6BR tight at 1K a hotter load is required.

Denis,

The 105gn Berger VLD has an average G7 BC of 0.272 (source: Bryan Litz using a firing-based experimental method) and according to the same authority, pointing improves BC by 3-7% dependent on the original meplat size and overall bullet calibre, (the smaller the calibre, the bigger the BC improvement for any given amount of meplat area reduction). So, let's be conservative, and say your pointing has effected a BC improvement of 3-5%, ie 0.280-0.285.

Using Berger Bullets' / Bryan Litz's Point Mass Ballistics Solver 2.0 g7 program, your terminal velocities at 2,850 fps MV are:

0.280 ...... 1,692 ...... 1,568 ...... 1,448 fps at 800 / 900 / 1,000 yards

0.285 ...... 1,710 ...... 1,587 ...... 1,469 fps

I'm not au fait with Queensland's climate, but since it's Oz and since this is late summer there, I've assumed 79-deg F, but left the environment as 29.92" HG pressure and zero % humidity. Add humidity / lower pressure, and those terminal velocities increase slightly - 7 or 8 fps for 50% humidity, a bit more for lower atmospheric pressure.

In any event, you're fine velocity-wise at 1,000 running around 1.3 MACH.

I used to shoot bench rest and F Class at 1,000 occasionally with this bullet in a 6BR at around 2,785 fps and didn't have any problems bar those engendered by my own incompetence.

What you're noting is that life is MUCH harder at 1,000 compared to 800yd, much more than the 25% increase in distance, and a ballistic fact of life. Of course, if your competitors are using even a 6.5X47L / 140gn VLD load, never mind a good 7mm with 180gn state of the art bullets, they have a significant advantage over you unless the conditions are very stable.

 

[Aussie Denis]

Thats a very detailed answer Laurie. You've explained logically exactly what I need to know. Thanks very much for your advice.

Denis.

 

[RDavies]

(making it clear, a 60 on the Ozzie target is similar to a 100 on the U.S target.
Denis, where were your 5s? Were they vertical or off to the sides? It could be that you are at the top end of the node and that going down .2 or so MIGHT help? Have you tried other milder primers over a chronograph?

 

[Aussie Denis]

Hi RDavies,

Sorry about the late reply. The dropped points were mostly horizontal but also vertical.

This weekend gone, I tried the same load at 400y where I should have hit 60's being the perfect distance for a 6BR. The wind was extremely light with boiling mirage twitching 45 degrees in either direction intermitently. The load performed exactly the same way it did at 1000y. I started investigating afterwards and identified a seating depth error in respect to where my known good load is. I'm pretty confident this is the cause and will try the same load again with a revised seating depth next weekend.

This factory Savage barrel has always been extremely sensitive to seating depth and has had me scratching my head before. I need to implement a step in my reloading where I regularly check the position of the lands so that I can chase them accordingly.

From forum responses I've had and speaking to people I'm now certain that its not a muzzle velocity or transonic zone issue which was my query at the time.

Thanks very much for your help though, I appreciate the response from you and everyone else..

Denis.