6BRA Fire Form and First Sizing Questions

[vegas]

Hey all,

I am curious about my new 6BRA set up as this is the first Ackley round I have loaded for. Started with 100 new Lapua brass, loaded with the standard 30gr Varget. Out of a 26" Criterion, getting 2810fps on first firing. Maybe one in five rounds had some heavier bolt lift. When I came to resize, I have an LE Wilson die with a .265 bushing. I used a Hornady Comparator to measure, not the best tool but has always been fairly accurate for me.

In measuring to set up the die for bumping back 2 thou, what I found was a fairly wide range of measurements, perhaps as high as 5 thou? Not knowing what I don't know, is this typical after fire forming?

Thanks.

 

[Ccrider]

Not for me. Using the same amount of powder and bullet to fire form with, I get fire form lens to within .002-3 thousandths. I forgot to add, I also seat my bullets long, hard into the lands at the same depth.

 

[60723]

After the 1st firing I wouldn’t set the shoulders back but .001. Some not fully formed until 2nd firing has been my experience.

 

[wkdickinson]

I've never found it necessary to load my bullets to jam for initial fire forming. Usually, at least with new Lapua 6BR brass, I find that there is some effort required to close the bolt. Which leads me to believe that the shoulder is "touching" the end of the chamber, because I load with .015 jump.

 

[a-dog]

Your brass is probably not completely fire formed, hence the discrepancies. It may take 2 or 3 firings to fully form. Don't use a comparator. Strip your bolt and size until the bolt just barely falls freely.

 

[G Liles]

After the 1st firing I wouldn’t set the shoulders back but .001. Some not fully formed until 2nd firing has been my experience.

I neck size only after the initial fireforming, then I strip my bolt and let the chamber tell me how much to bump the shoulder back.

 

[moondog]

As stated above, you probably don't need to bump the shoulder. Check a dozen or so once fired cases. I'm betting the bolt closes fine on them. You may need to trim though, at least I did.