6mm BRX Case Length Question

[rcw3]

When you fire form 6BR brass to 6mm BRX brass, what are you generally coming out with as the length of the fire formed brass case?

Robert Whitley

 

[BillHocker]

Robert,
Using Lapua brass, the fireformed length was 1.544 - 1.545
Bill H

 

[johara1]

Robert,
You can vary the length by the load. The chamber and cases should be free of lube.No body seems to talk about this at all. I can change the length of a Dasher from 1.545 to 1.560+ by the powder, bullet and the temp. of the chamber.Most of all it has to be free of lube...........jim

 

[TheBlueEyedBear]

Jim,
Without any lube on the case how does the fire-forming work as related to neck splitting? I always use a little lube on the shoulder area to prevent splitting. My cases normally shrink to 1.544 pretty consistently.

 

[rcw3]

Thanks everyone - I was trying to get an idea of the typical "shrink factor" and theses postings get me "in the ballpark", which is what I was looking for.

Thanks again!

Robert Whitley

 

[johara1]

if you have lube it makes the case short. Your chamber or should be around 1.570 so do you think a blow length of 1.545 is good? your .010 to.015 short of trim length.you need the case to grab the chamber walls to make it stay the same length.....jim

 

[rcw3]

if you have lube it makes the case short. Your chamber or should be around 1.570 so do you think a blow length of 1.545 is good? your .010 to.015 short of trim length.you need the case to grab the chamber walls to make it stay the same length.....jim

I am well familiar with fire forming brass, blowing shoulders forward, etc. and never use lube on the cases. I know there is a shrink factor, but I did not have an idea about what it was for a BRX.

My point in asking the question was to determine at what length I wanted to make the "max chamber" length on my reamer. There is going to be a "shrink factor" when you fire form BRX brass, and it looks like 1.445" may be about what it will wind up to be in overall length, and for me 1.560" for a max chamber will work fine since I also don't want to be trimming brass all the time either (i.e. a standard 6BR 1.570" max chamber is long considering the shrink factor).

Robert Whitley

 

[johara1]

Robert,
Some lots of brass are short 1.550 most are1.555-6 and i've seen 1.560. there are so many variables, i have one lot that is hard, it makes radial cracks on the shoulder. I call on that and they never returned the call. now the average length is 1.555 so that what you shoot for and keep down to 1.550, they will grow for two more firings then trim. I clean my loaded rounds and chamber with a solvent and form cases for fowlers l the chamber gets warm and they start to get short......jim

 

[johara1]

Robert,
One thing i forgot don't use wolf srm primers,that will make them short also i use cci . The other thing there is no shrink factor they will remain the same length down -.005 if you load to get the length...jim

 

[6BRLongRange]

I have fireformed 300 pcs for a BRX I just had built, using 29.5 Varget, 107 SMK with .003 tension seated .050 long and had excellent results. I was told by seasoned BRX users if you use this load for the first two formings, then work up to your desired load/velocity the cases would last longer without loose primer pockets. I use imperial to size with and simply wipe it off with a clean rag and have no issues at all. Brass is 1.545-1.560 after second froming when I trim. Hope this helps. BTW have shot groups at 300 yards in the .500"-.625 "range after fireforming. Will shoot in the .750" range at 300 yards while FFing.

 

[johara1]

6brlr,
I too us SMK but the 115 DTAC I have no luck with berger.You found the load that works but 2.445-460? what are you shooting? Brass is 1.555........jim

 

[rcw3]

johara1

I think 6BRLongRange means 1.545" - 1.560" instead of "2.445-460" - some typos there but we get the idea.

Robert Whitley

 

[AlNyhus]

Robert,
Some lots of brass are short 1.550 most are1.555-6 and i've seen 1.560. there are so many variables, i have one lot that is hard, it makes radial cracks on the shoulder.......jim

Jim, you are dead on about some Lapua 6BR cases being 'hard' and cracking in the shoulder area.

I first ran into this when f-forming cases for my 30 WolfPup...which is a 30BR with the shoulder blown forward .240 and an .085 long neck. Initial lots were fine, but later lots were a much different story. Even with careful and aggressive stress relieving, these cracks happened. It's clear that the material itself is different than the earlier cases.

I just finished f-forming 50 cases for a 30BRX. I feel it's imperitive to stress relieve the cases before blowing the shoulder forward, even with Lapua's factory 'annealing'. After the first firing, they need to be stress relieved again before any serious load work begins. This goes for any cases where the shoulder has been f-formed forward...no matter if it's a Dasher, BRX, etc. Lightly lubing the cases before f-forming allows the case to better conform to the chamber. Since the pressure drops off so rapidly when f-forming a BRX style case...due to the case volume expanding as the cases internal dimensions increase...you need to decrease the cases ability to 'grab' the chamber walls, thus allowing the back end of the case to firmly stay in contact with the bolt face. A coned bolt/sliding plate extractor action helps in this.

Just my approach to it.

 

[6BRLongRange]

johara1

I think 6BRLongRange means 1.545" - 1.560" instead of "2.445-460" - some typos there but we get the idea.

Robert Whitley

You're correct Robert, typos. I corrected the post to deter confusion.

 

[savageboy]

AlNyhus- can you explain what you mean by "stress releive" the cases. Do you mean just lightly lube them? Imperial wax or what ?
Thanks, Getting ready to do some 6brx and would like the cases to last longer than they do in my 260AI.

 

[AlNyhus]

AlNyhus- can you explain what you mean by "stress releive"? Thanks

It's just my way of refering to 'annealing'. The subject of 'annealing' gets pretty confusing, so it's probably better to refer to it as 'strss relieving'....which is what we're really doing.

Sorry if I sidetracked the thread........ -Al