Chambering 6BRA?
- Thread starter dlwheel
- Start date
Pt&G makes a Go guage that has 40 degree shoulder and is .004 shorter. I have one on order.
Thanks for the heads up. I had no idea they made AI gauges. I got one ordered!
-David
Do you have a link to the gauge that is needed?
Thanks
Alex Wheeler
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A measurement from the barrel shoulder to the back of the HS gauge thats .004" longer than the measurement from the action face to the bolt face.
Do you have a part number?
You wouldn’t go .006-.007 longer to account for crush while torque-ing?
Go to the PT&G website and click on gauges, then headspace gauges, then wildcat gauges. After this scroll down to near the bottom of this group and you will see one for the 6mm BR AI. Good shooting...James
tom
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No wonder my BRA chambers have been costing me so much more than others, it's all the extra math
Tom
Alex Wheeler
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I dont really experience crush. I would be looking at your setup or machine work if you are seeing .002-.003" change in headspace by torquing the barrel.
How would either of these effect crush? Wouldn’t that be a barrel/action materials property?
I’m just asking because it seems that allowing for .002ish of crush seems to be the consensus of what I read online, but I’m no expert and only get to chamber guns for myself which is like 1 barrel a year so I don’t have the number of trials on my resume to come up with my own statistics. On my own two personal builds, I only saw .0015
Alex Wheeler
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If you had a rough shoulder or if your barrel was shifting in the lathe and threads were not square to the shoulder. Thats a couple reasons. Just think about whats happening. The shoulder of the chamber is in front of the shoulder on the barrel. For that chamber shoulder to get closer to the bolt face with torque something is compressing. On good custom actions I just do not see crush.
I agree with Alex. I see people talk about crush all the time with their chambers. The only situation I have ever experience this is with factory remingtons that haven’t been trued. Crooked action face, untrue recoil lug In this situation you will have crush. Otherwise you shouldn’t ever experience this.
urbanrifleman
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I took a 6br gauge and turned 4 thou off the back.
A lot faster than waiting for ptg.
A lot faster than waiting for ptg.
Yeah, I don't know how this "crush" got to be the rule everyone parrots as gospel. If everything comes squarely in contact as you tighten it, any "crush" would have to be the threads stretching,but headspace would remain unchanged in that scenario. If my math is ok tonight, at 18TPI, 0.002" of travel would require 13 degrees of turn. Does it seem reasonable for the barrel to continue to turn that much after full contact on assembly? I don't think so.
Unless your receiver, lug, or barrel shoulder are crooked, then you could crush them together and see headspace changing, but then the question is: how true is your bolt face to the bore when you're "tight enough" to achieve the correct headspace? I'd take apart and fix any gun that changed headspace as I tightened the barrel on.
To the original question, and perhaps better directed at gunsmiths here @Alex Wheeler : Do you need a custom go gauge for this, or do you run your chamber by the numbers and use a standard 6br go-gauge as your no-go gauge to make sure you've not cut it too deep? I'm not a gunsmith, so I'm perhaps not thinking about the liabilities correctly, but it seems with a wildcat chambering like the 6 BRA, there is no need to fall within traditional go/no-go gauge limits that are created purely for safety with SAAMI off-the-shelf ammo.
Alex Wheeler
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From the very first barrel ever engraved 6BRA, I have used a 6 br go and held .004" short on it.
DJSBRS
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And that is how I set up for the 6BRA hydro formed brass for your customers Alex. No issues for chambering at all.
DJ
DJ's Brass Service
205-461-4680
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