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.

 

[vegas]

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

This is what I was assuming. Good to confirm it, thanks.

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.

Thanks, will try that after the next firing.

I have been loading for over 10 years and still learning

 

[BoydAllen]

If you want to do an accurate job of setting up your FL die using once fired cases, consider this method. First of all you need to remember why we bump, and why we try to not bump too much. Assuming that you know both answers, deprime a case,, cover the head with Scotch tape, after first verifying its thickness by folding it on itself and measuring the two thicknesses. What you are creating is a case that the bolt will not close on, with ordinary pressure. Don't force. Then you start carefully adjusting down your die with slight adjustments and measurements, each time you dry all the lube off and check it in the rifle. At some point you will find a point where with almost no point you can lower the bolt handle and it will stay where you put it. I use this as my zero point. This is my point of reference for setting bump. Normally I load at the range, and when I am doing that I neck size and fire a single case with a warmest load that is safe, until the datum to head measurement no longer increases, then I set my die in relation to that case. Typically, after one firing, if you set your die to duplicate the datum to head measurement of the fired case and try it in your rifle the bolt will close with no problem which tells you that you have clearance and do not need to decrease your datum to head measurement below what that case measures. It is common for there to be variation within a set of fired cases so you may want to measure and try several, working with the one with the largest measurement.

Finally, one tip. The easiest method that I have found to get a primer out of the way before taking a measurement is to simply reseat the fired primer in the case, with a good heavy squeeze, That will get it well below the head and it will be removed in the course of normal sizing. Another tip for bushing dies, so as not to over work a case's neck I remove the bushing while adjusting the die, and after it is set replace it and size the neck. The fastest way to get a bushing out of a die that is in a press is to take the top off of the die and shove a neck brush through the bushing and pull it out.

 

[Jet]

30.0 Varget is pretty standard for fireforming BRA brass. What action are you using?

 

[SSchnd]

Make sure the cases fired are deprimed.

I always do this for shoulder measurements when setting my die.

I run Lapua brass. And .272 no turn chamber and use .268 bushing in Wilson for neck. I was running .267 bushing but felt my mandrel was a little better fell at .268 now.

I use my same charge weight for forming but may touch the bullet. Nice part of the BR brass is the neck / shoulder touches the BRAI chamber and you should feel just a little pressure on the bottom if the bolt close.
Agree with above, My current FF brass I am firing 2nd time before being sure I am happy with forming.

 

[Sheldon N]

@BoydAllen description above is very good. On a similar vein, if you are a visual learner go to the link below and watch the video "sizing brass".

Videos | wheeleraccuracy

www.wheeleraccuracy.com

I like to use this method to find the shoulder datum measurement that just barely gives me a freely dropping bolt handle. I want zero resistance on bolt close, but no extra sizing beyond that point. Once you have that shoulder datum measurement, you can size all your brass to that target number for the rest of the barrel life.

One other trick you can do when you first fireform brass and it's not yet fully expanded to the chamber.... if you back the FL sizing die out by a full turn or so, it will not touch the shoulder at all and will just act as a body sizing die constricting the diameter of the case body. That body sizing will actually push the shoulder forward by 0.001 or sometimes even 0.002. That can sometimes be enough to let you feel bolt close resistance and then carefully bump the shoulder back in half thou increments until the bolt close resistance goes away and you get your sizing target. You may be able to avoid using scotch tape with this approach.

 

[BoydAllen]

@BoydAllen description above is very good. On a similar vein, if you are a visual learner go to the link below and watch the video "sizing brass".

Videos | wheeleraccuracy

www.wheeleraccuracy.com

I like to use this method to find the shoulder datum measurement that just barely gives me a freely dropping bolt handle. I want zero resistance on bolt close, but no extra sizing beyond that point. Once you have that shoulder datum measurement, you can size all your brass to that target number for the rest of the barrel life.

One other trick you can do when you first fireform brass and it's not yet fully expanded to the chamber.... if you back the FL sizing die out by a full turn or so, it will not touch the shoulder at all and will just act as a body sizing die constricting the diameter of the case body. That body sizing will actually push the shoulder forward by 0.001 or sometimes even 0.002. That can sometimes be enough to let you feel bolt close resistance and then carefully bump the shoulder back in half thou increments until the bolt close resistance goes away and you get your sizing target. You may be able to avoid using scotch tape with this approach.

The only problem is when folks do not actually do before and after measurement. If a die is too large to work with a particular chamber by the time you get the feel that you want the shoulder may be pushed back too, and with that die setting you will eventually damage brass.