Gunsmithing 6MM BR AI GO/NO GO question

[Tigerfan601]

I currently have a 6BRa reamer on the way from PT&G. My question is I didn't add the go/no go gauges to my order soon enough so if I order them now ill get them 3 weeks after the reamer. I have heard of people using 6BR GO/NO GO gauge's in their BRa, but wanted to make sure that is correct and what the process is on doing that to ensure that you get .004 crush on BR brass when fire forming. Thank you for any help or information.

 

[Mordamer]

I'd use 6 BR virgin brass to set headspace. I'd chamber it where you just feel a little bit of resistance on bolt close on a piece of virgin 6 BR brass. This ensures that the neck/shoulder junction on the brass is nice and tight in the neck/shoulder junction on the chamber. Check with several pieces of brass and use the tightest one as your gauge. This ensures that all the others will fit for fire forming.

 

[Tigerfan601]

I will surely tell my gunsmith that. I appreciate the information.

 

[wnroscoe]

I'd use 6 BR virgin brass to set headspace. I'd chamber it where you just feel a little bit of resistance on bolt close on a piece of virgin 6 BR brass. This ensures that the neck/shoulder junction on the brass is nice and tight in the neck/shoulder junction on the chamber. Check with several pieces of brass and use the tightest one as your gauge. This ensures that all the others will fit for fire forming.

The Datum Line on the 6BRA is different than the Datum Line on the 6BR. This really isn't sound advice. The Op should order a proper go gage and chamber the right way.

 

[wnroscoe]

I currently have a 6BRa reamer on the way from PT&G. My question is I didn't add the go/no go gauges to my order soon enough so if I order them now ill get them 3 weeks after the reamer. I have heard of people using 6BR GO/NO GO gauge's in their BRa, but wanted to make sure that is correct and what the process is on doing that to ensure that you get .004 crush on BR brass when fire forming. Thank you for any help or information.

Check JGS for a 6 BRA Go Gage. They might have one on the shelf.

 

[Mordamer]

The Datum Line on the 6BRA is different than the Datum Line on the 6BR. This really isn't sound advice. The Op should order a proper go gage and chamber the right way.

The datum line means absolutely nothing for the method I described. In fact, the method I described is exactly how Mr. Ackley wrote that Ackley Improved chambers should be cut. This is because using this method matches the chamber to the brass and not some random gauge that may or may not match the brass. The method I described keeps brass stretch at the web of the case to a minimum during the fire forming process.

If you claim it is not sound advice please give some kind of context to your claim or a possible reason why.

 

[wnroscoe]

The datum line means absolutely nothing for the method I described. In fact, the method I described is exactly how Mr. Ackley wrote that Ackley Improved chambers should be cut. This is because using this method matches the chamber to the brass and not some random gauge that may or may not match the brass. The method I described keeps brass stretch at the web of the case to a minimum during the fire forming process.

If you claim it is not sound advice please give some kind of context to your claim or a possible reason why.

I use gages as a standard for head spacing, not rifle brass that's all over the place. When you blow out the case and change the shoulder geometry things change. The BRA utilizes a very different shoulder angle than the standard BR. That alone means the Datum Line "does matter" as that's where the case head spaces. All of my AI go gages are very different than the standard parent cartridge go gage. Everything's changed since the PO days, what's your point?????????

 

[wnroscoe]

I use gages as a standard for head spacing, not rifle brass that's all over the place. When you blow out the case and change the shoulder geometry things change. The BRA utilizes a very different shoulder angle than the standard BR. That alone means the Datum Line "does matter" as that's where the case head spaces. All of my AI go gages are very different than the standard parent cartridge go gage. Everything's changed since the PO days, what's your point?????????

The only AI vs standard prints I currently have on hand are for the 22-250 and 22-250AI. Yea, I know, not the BRA. When comparing the standard 22-250 and 22-250AI version there is a datum line difference of .022". I can assure you, the 6BR and 6BRA are not equal at the datum line. My comments aren't based on a guess. I'm done, ya'll do as you please. I've been around the block, seen it done it, got the T-Shirt.........

 

[Tigerfan601]

I have gauges ordered but will be in later than the reamer. My gunsmith does have a 6BR go and no go gauge though.

 

[Supersubes]

I use gages as a standard for head spacing, not rifle brass that's all over the place. When you blow out the case and change the shoulder geometry things change. The BRA utilizes a very different shoulder angle than the standard BR. That alone means the Datum Line "does matter" as that's where the case head spaces. All of my AI go gages are very different than the standard parent cartridge go gage. Everything's changed since the PO days, what's your point?????????

William, what Mordamer describes is the way it used to be done and is successful, those are his only points. It works fine. Like you, he understands the datum differences.

 

[Sheldon N]

I have gauges ordered but will be in later than the reamer. My gunsmith does have a 6BR go and no go gauge though.

Alex Wheeler the benchrest gunsmith who helped popularize the 6BRA chambers his set at 0.004 short of a 6BR go gauge. When my gunsmith did mine I sent him a piece of brass and he checked against that and it measured about 0.003 or 0.0035 short of a 6BR go gauge, so basically the same.

I would say just chamber 0.004 short of a 6BR go gauge and you'll be fine. That's how the majority of these are being chambered.

 

[wnroscoe]

So, after reviewing several reamer prints and talking to JGS about the chambering, dimensional changes were ground into the "6BRA #1" reamer that was designed by Alex Wheeler that allows you to use a standard 6BR go gage. As I understood JGS, the #1 reamer had changes made as compared to the original BRA reamer. Chamber as per normal with no crush fit. Slight felt contact on go but that's it. I still don't recommend using a piece of virgin brass to set headspace.

 

[cockcroft]

Ackley cases head space on the neck shoulder junction, not the datum spec'd for the parent cartridge . The crush fit is at the neck shoulder junction, not in the area between the neck and shoulder where a datum line is normally checked.

Chambering a 6brai using a standard 6Br gauge, I leave .006 gap between the face of the action and the shoulder of the barrel with the bolt closed on the gauge. Take out the gauge, torque up the barrel and have a .004 shorter chamber to get the tight fit(crush) on new case. This is for a shouldered barrel, not a barrel nut setup.

 

[Shanerbanner10]

add .004" to your headspace measurement if you're using a BR gauge for a BRA chamber. i.e. on an Impact barrel we the print calls for a .948" headspace measurement. When cutting a BRA chamber using a BR headspace gauge simply add .004 to your headspace measurement... .948" + .004" = .952". This will get you the perfect amount of crush on virgin BR brass for fireforming. You should not have to jam or anything like that.

 

[Steelnecktie]

You chamber to .004” short on BR then chamber to .084” short on dasher go gauge. Should be little bit of resistance when bolt reaches bottom with factory Lapua BR brass