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.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.
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.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
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.
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...)
How do you measure the .004" crush?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.
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.
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.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.
Who said anything about putting shims between the bolt and go gage?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?