6 dasher brass - blow length??

[operator1]

Just built a 6 dasher and am trying to get my brass fireformed. I am using the false shoulder method with 30.5 gr Varget, 107 smk and cci 450 primer. I am using Lapua blue box brass and am getting 1.538 after fireforming. Chamber is 1.555. Is this too short? Any advice on how to get better results?
Hotter load?

 

[22BRGUY]

My experience so far is that it takes 2 firings to get the shoulder sharp.

 

[Bkluke]

Ever since the blue box came out my blow lengths have been 1.540 on an average.

I use the false shoulder method as well, the only thing I noticed, by jumping the bullet it will blow a little longer. :-\

Don't know what changed, but I was able to blow them out to the 1.555 with the brown box brass.

 

[painless2]

You are right on the money. mine come out 1.542 avg. you dont want the cases to be any longer than 1.545, or you will have to trim.
Tom

 

[potatoe]

Mine formed brass was an average of 1.540 also. I wouldn't worry about it with a 1.555 chamber length.

 

[lloydx2]

Blue box 6 br brass can be as long as 1.555. So might keep that in mind when chambering. My blow lengths are 1.542 avg. And sometimes shorten up more after 2 fireing as shoulder and straighter body taper fully form. I never have gotten wrapped up in over all length (blow length) I look for consistency in length from case head to a datum line on the shoulder To me this seems more important. Just a thought Lloyd

 

[johara1]

With a chamber length of 1.555, so the case can't move so a false shoulder is a waste of time. Dry everything,get all lube off cases and chamber then adjust your load for length. If the chamber is too smooth it will make short rds. Mine run around 1.550-.552......jim

 

[lloydx2]

With all do respect. When fireforming 6br to dasher, less body taper and more shoulder angle The brass has to go somewere. When it does the case shortens up. Considerably. My comment about chamber length was more about chambering a virgin untrimmed peice of lapua brass. No matter how your fireforming it. To be a little more specific about case headspacing being important. I have measured fireformed cases in 3 places on the shoulder 400-375-350 diameter comparator inserts. I am seeing .001 difference with formed cases. when I measure aol on the same cases I'm seeing as much as 003 difference. With Kiffs (world record) dasher reamer 271 nk .124 fb 1.560 oal case length chamber. Fireforming 31.5 grs varget 107mk 108brg On first firing Ive had to bump cases so the bolt drops with no resistance (no striker assm). So there defiantly getting there. These cases all measure 1.540-543 oal before trimming. This load might be a little spicy. I know some that run 33grs fireforming. Remember this is what I'm seeing in my setup We all know theres no one chamber for this cartridge and therefore There CAN and WILL be a difference.

 

[johara1]

I use no less than 9 different Dasher barrels, And if you do it right they will be 1.550. My barrels will shoot in the low 1's and zero's. I don't know about world record reamers but mine are 1560 chamber length. The free bore is .155 and one is .135 and a .266 neck. I fire form at 1.550-52 in a one barrel does a good job after i used 120 grit in the chamber. At 1K my groups at Va. 1000 BR. are 4.1 agg. for the light gun so far this year.........jim