Length of 6 dasher brass after fire forming

[marwitz89]

I just got done fire forming 125 pieces of 6 mm BR into dasher and had a question about the length after fire forming. I used the following process to fire form:

I measure the blue box Lapua brass and most of it was 1.550 with some of it at 1.545 and 1.540. There were very few that were 1.555 or longer.

1. I have a .266 chamber so I turned the necks to create a false shoulder. The bolt would close with slight resistance on this false shoulder.
2. I used a 108 BT bullet jammed .020 behind 30.3 grains of Varget with .003 neck tension.
3. I cleaned the chamber and the brass with non-chlorinated brake cleaner often while fire forming.

After fire forming, I measured every case. The average length I saw was about 1.544 to 1.548. I would say I had 15 that were 1.550 and maybe 15 that were between 1.541 to 1.544.

I'm curious if others are seeing the same length and have the following questions:

1. Should I fire them again to see if they will grow a little longer prior to trimming?
2. Should I trim them all to the same length? I wanted to trim them all to 1.550 but it doesn't appear that will be possible.
3. The reamer is specd. to a 1.560 length. Will I have an issue if I trim them all to 1.545?

Thanks for any help and advice you can give.

Joe

 

[22DASHER]

1. Should I fire them again to see if they will grow a little longer prior to trimming?
2. Should I trim them all to the same length? I wanted to trim them all to 1.550 but it doesn't appear that will be possible.
3. The reamer is specd. to a 1.560 length. Will I have an issue if I trim them all to 1.545?

1. No. Mine never changed more than .001 after initial forming.
2. Yes. I would trim them now, start load development.
3. No. This is pretty much the same with everyone shooting Dashers.

 

[Jet]

I follow very similar steps and get 1.544-1.546 OAL. I have not been able to get them any longer with trying different methods.

I would fire them one more time with your normal load (start load development) then trim.

Good Shooting.

Rich

 

[dmoran]

I don't do much final case prep (or qualifications) until after the 2nd firing. After the 2nd firing is when I see that most all aspects have settled down.
If you do choose to trim after FF to fit your chamber or what ever reasons, is okay, just that they will need trimming again sooner. Seems like they don't grow evenly/squarely until after the 2nd firing is primarily why - IME.

My 2-Cents
Donovan

 

[ridgeway]

Try cleaning after 5 shots. Swab chamber with brake cleaner after cleaning.

 

[marwitz89]

That's exactly what I did after every 3 shots.

 

[CaptainMal]

Yesterday I trimmed about 100 that were shot twice. Most did get to the 1.550" length but just barely. A few did not and my experience tells me they never will.

Close enough for me though.