6 BRA headspace question.

[cast1]

Is the .004 crush for headspace on a BRA before or after torquing the receiver? I usually get about a thousandths crush when I tighten.

 

[Northridge]

Is the .004 crush for headspace on a BRA before or after torquing the receiver? I usually get about a thousandths crush when I tighten.

my experience would be after tightening but if your a tad less crush the result still will be the same with out heavy heavy close on bolt, there is a fine line in regard to much load on bolt when closing risk of galling go's way up. some will say .002 crush will not hold case enough to form well but they are completely of base.

Shawn Williams

 

[Geno C]

my experience would be after tightening but if your a tad less crush the result still will be the same with out heavy heavy close on bolt, there is a fine line in regard to much load on bolt when closing risk of galling go's way up. some will say .002 crush will not hold case enough to form well but they are completely of base.

Shawn Williams

I have seen plenty of cases shorter than .002" short of .000" headspace. When I'm moving brass around more than just a standard case in a matching chamber, I prefer to have the shortest case be at .000" of the chamber. So if I find the shortest case is .005 short of .000" of the parent case, I want my chamber to be at least .005" short of the parent case.

All my improved rounds like this are .007" short of the parent case. Never had a problem galling lugs with a little light grease on them and I don't stretch any cases either. (I might be a little superstitious though...)

 

[Alex Wheeler]

Good actions and machining usually do not result in a change of headspace after torquing in my experience. All headspace measurements should be in the final state, meaning if you are seeing a change after torquing the measurement should be taken at that time. I do .004" crush on a br go gauge. Feed back has been everything from a perfect fit to having to bump the cases a couple thou to fit. There is variation in brass as well as how deep you cut into the shoulder when neck turning as thats the point headspacing occurs on the first firing. I would rather you had to bump the shoulder than have a loose fit.

 

[cast1]

Good actions and machining usually do not result in a change of headspace after torquing in my experience. All headspace measurements should be in the final state, meaning if you are seeing a change after torquing the measurement should be taken at that time. I do .004" crush on a br go gauge. Feed back has been everything from a perfect fit to having to bump the cases a couple thou to fit. There is variation in brass as well as how deep you cut into the shoulder when neck turning as thats the point headspacing occurs on the first firing. I would rather you had to bump the shoulder than have a loose fit.

Thanks guys. I torque to about 90-100 ft/lbs which may be more than necessary but that’s what I’ve been taught (tactical type builds). I seem to lose just a smidge of headspace when I torque to that degree. Is that a big mistake?

There’s also differences I guess in who grinds your go gauge. I went .003 short on my 7 br gauge from JGS and I still seem to get plenty of crush before torquing the receiver.

When I go to find the lands for this rifle using Alex’s method, I will just take a piece of brass and bump the shoulder for a loose fit in the chamber yes?

 

[Hanbleceya]

I have seen plenty of cases shorter than .002" short of .000" headspace. When I'm moving brass around more than just a standard case in a matching chamber, I prefer to have the shortest case be at .000" of the chamber. So if I find the shortest case is .005 short of .000" of the parent case, I want my chamber to be at least .005" short of the parent case.

All my improved rounds like this are .007" short of the parent case. Never had a problem galling lugs with a little light grease on them and I don't stretch any cases either. (I might be a little superstitious though...)

Superstition is sometimes intuition. And intuition has literally saved my life at least twice.

 

[Blop]

For those of you that neck turn the virgin 6BR brass... did it affect your crush fit at all when turning into the shoulder?

Looking to have mine chambered this week -.004... would rather turn prior to forming. This is my only concern.

 

[Clancy]

My BRA was chambered yesterday by Beanland. .004 crush fit. I’ll pick it up next week once it has been bedded.

I plan on fireforming with some 80 gr Bergers then moving on to the Hybrid.

 

[Old Navy]

Good actions and machining usually do not result in a change of headspace after torquing in my experience. All headspace measurements should be in the final state, meaning if you are seeing a change after torquing the measurement should be taken at that time. I do .004" crush on a br go gauge. Feed back has been everything from a perfect fit to having to bump the cases a couple thou to fit. There is variation in brass as well as how deep you cut into the shoulder when neck turning as thats the point headspacing occurs on the first firing. I would rather you had to bump the shoulder than have a loose fit.

How do you measure the .004" crush?

 

[Dave@MAM]

Zero headspace -.004”. Found by calculating the headspace from measurements of receiver and bolt dimensions. Best way, I think, is to have barrel in machine, an action with stripped bolt in hand and thread it onto tenon with gage installed, screw on and make adjustments by going deeper with the reamer. When you get to the point you have a .004 gap measured with feeler gauge between barrel shoulder and receiver face, you are golden.

 

[Old Navy]

Re-phrase:
How do you measure the .004" crush on a pre-fit?

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[Link]

If you have a few thou to much cruse in the chamber, you can use a competition shell holder to compensate , right ?
Don

 

[dnellans]

Zero headspace +.004”. Found by calculating the headspace from measurements of receiver and bolt dimensions. Best way, I think, is to have barrel in machine, an action with stripped bolt in hand and thread it onto tenon with gage installed, screw on and make adjustments by going deeper with the reamer. When you get to the point you have a .004 gap measured with feeler gauge between barrel shoulder and receiver face, you are golden.

This is -not- how you get .004 crush fit, just for future thread readers. What he’s describing is go +.004 which is .008 off of the target being described by everyone else.

Edit - I misread his original post and thought he was shimming behind the go which is the wrong direction. If you shim .004 between the shoulder and action face, chamber to br go, then remove that shim, you will indeed get go minus .004.

 

[KRP]

This is -not- how you get .004 crush fit, just for future thread readers. What he’s describing is go +.004 which is .008 off of the target being described by everyone else.

His description of zero headspace +.004 should have been -.004 but the described procedure is correct using a BR go gage. The parent cartridge go gage becomes the no go for any Ackley improved cartridge.

 

[dnellans]

His description of zero headspace +.004 should have been -.004 but the described procedure is correct using a BR go gage. The parent cartridge go gage becomes the no go for any Ackley improved cartridge.

Unfortunately, nothing about that description is right. If you’re chambering .004 short on a BR go, You won’t be able to close the bolt on the go, and thus putting additional shims between the bolt and the go doesn’t make sense.

To chamber .004 short of a br guage you have to do it by measurement, you can’t use the action to test fit on a stock length go.

JGS will sell you a .004 short BR go however that will let you check fit like a traditional go, but again, if you can close on this go plus shims, you’ve missed your .004 short target.

What I find odd is that they don’t just make a 40 degrees shoulder bra gauge, if they’re willing to sell you a BR -.004. @Alex Wheeler any idea why that is?

 

[KRP]

Nothing about that description is right. If you’re chambering .004 short on a BR go, You won’t be able to close the bolt on the go, and thus putting additional shims between the bolt and the go doesn’t make sense.

To chamber .004 short of a br guage you have to do it by measurement, you can’t use the action to test fit on a stock length go.

JGS will sell you a .004 short BR go however that will let you check fit like a traditional go, but again, if you can close on this go plus shims, you’ve missed your .004 short target.

What I find odd is that they don’t just make a 40 degrees shoulder bra gauge, if they’re willing to sell you a BR -.004. @Alex Wheeler any idea why that is?

Who said anything about putting shims between the bolt and go gage?

He's cutting the chamber so there is a .004 gap between the barrel shoulder and action face with the go gage in the chamber. When he removes the go gage and tightens the barrel the headspace dimension will be .004 shorter. What is incorrect about that?

 

[dnellans]

Ohhhhh - you’re totally correct. I mis-read his post as putting a .004 shim behind the go, not between the shoulder and action face. Chamber to zero like than and then pull the shim works, I agree.

 

[newbieshooter]

 

[Nick Caprinolo]

I am just starting a 6BR build. It is in the hands of my gunsmith. All of this is giving me a headache. I don't seem to grasp what the devil every is talking about. Maybe I am too old for this stuff.

 

[dnellans]

6BR you have nothing to worry about - put the brass in and shoot!