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Topic: Tuning the 6 BRA at 600 (Read 955 times) previous topic - next topic

Re: Tuning the 6 BRA at 600

Reply #15
I get it but that means you have to work your brass a lot more...

Re: Tuning the 6 BRA at 600

Reply #16
.014 seems excessive. That’s 2-3x a typical FLR
Have you checked your actual chamber dimension for total cartridge length?
I’ve experienced it myself from not trimming enough. If the bolt face is slammed you’re adding that much to the trim length. I think I remember Josh telling me there is a spec for clearance between bolt face to barrel of .012-.014” to allow gas to escape in an overpressure situation. Just a thought.
RIP Chris Cornell

Re: Tuning the 6 BRA at 600

Reply #17
.014 seems excessive. That’s 2-3x a typical FLR.          My point exactly


Have you checked your actual chamber dimension for total cartridge length?         No how would I do that?


I’ve experienced it myself from not trimming enough. If the bolt face is slammed you’re adding that much to the trim length. I think I remember Josh telling me there is a spec for clearance between bolt face to barrel of .012-.014” to allow gas to escape in an overpressure situation. Just a thought.

I've never given the bolt to breech any thought before I always assumed the go / no go gages took care of that.
Dave

Re: Tuning the 6 BRA at 600

Reply #18
I've never given the bolt to breech any thought before I always assumed the go / no go gages took care of that.

https://www.brownells.com/reloading/measuring-tools/case-gauges-headspace-tools/sinclair-chamber-length-gage-prod32925.aspx

Or sacrifice a case. Set your bump at .002” based on your fired case dimensions and keep trimming a couple thousands off your total case length and  see if bolt frees up.
RIP Chris Cornell

Re: Tuning the 6 BRA at 600

Reply #19
I've never given the bolt to breech any thought before I always assumed the go / no go gages took care of that.
Go/no go only checks headspace.
RIP Chris Cornell

 

Re: Tuning the 6 BRA at 600

Reply #20
I'm thinking I have the headspace too loose. Everthing I'm reading says in an AI chamber the go gage becomes the no go gage because you need .004 crush on the parent case.
Dave

Re: Tuning the 6 BRA at 600

Reply #21
I get it but that means you have to work your brass a lot more...

I get what you're saying but I'd rather things work like they're supposed to versus ordering some expensive custom made die that's a one off for something I'm not interested in duplicating!
Dave

Re: Tuning the 6 BRA at 600

Reply #22
Reset the head space this afternoon. Tightened the barrel up hand snug to a 6 BR case and it was tight on a go gage, pulled the case out and snagged it a little more and had bolt to breech contact. Backed it out until I had bolt to breech clearance then it had a little drag on a go gage and would barely start on a no go.

Test fired two pieces of new brass and with a .006 bump they chamber with a little resistance. So I think I made progress and I'm going to fire those two a second time and see how they eject and resize but won't get to it until next week. Still have the goofy two angles on the shoulder but it almost cleans up with the .006 bump.

Maybe my ff load isn't hot enough to blow the shoulders out but the die and brass are making contact at the shoulder body junction.
Dave

Re: Tuning the 6 BRA at 600

Reply #23
The case on the left is pushed back .014 and chambers nice! It is outside turned, that is the shiny line just below the neck shoulder junction where I cut into the shoulder.

The case on the right is fired not resize. It is inside reamed, that shiny line just below the N / S junction is the light on the different angle. To make this case chamber like it should requires a .014 bump.


Dave,
I believe you may be correct on the faulty or at least "off spec" chamber.  It certainly looks suspect. The secondary angle may have been cut to eliminate donuts in that case your die would need a similar cut.  I also believe the .014 you are "bumping" is your die squeezing out the "second" angle.  If you were truly bumping .012 or 014 at the shoulder your brass would probably be toast after a couple of firings.
In this link is a photo of a 6bra and the second angle isn't there.
https://www.wheeleraccuracy.com/6-bra
Not knowing the history of the barrel my suggestion would be to set it back a little and recut the chamber with a different reamer.  Of coarse special throating might come into play to get you where you are now.  Second option would be to cut a corresponding chamfer or radius in your die.
Not knowing how much the cheapest dasher die would cost,  it might be worth it to modify one (shorten & radius).  A "cheap" experiment!
Last thought, a new 6br case set real snug as a headspace gauge would be real close if the 6bra reamer was correct.  The 6br go gauge would now become the no-go for the Ackley chamber.  However if your chamber is truly goofed up then none of these "gauges" would be right.  If you used the 6br go gauge originally and the chamber was screwed up it might of went too deep.  This may have been the cause of your bolt head hitting the breech face.
Food for thought.
IMHO,
Randy
11X Grandfather
Part time Savagesmith

Re: Tuning the 6 BRA at 600

Reply #24
@mnbogboy  you're pretty much correct on everything above. It's either a flaw in the chamber or I'm not getting the shoulders blown out on ff. I don't really think it's the latter but I'm going to load some new brass up a little hotter and see if it cleans up the shoulder.

The smith that cut the chamber has been contacted but is out of the country and unable to to do anything about it for a couple weeks.

I'm really hoping it's something I'm doing and not something he did so I can get it squared away on my own but I'm running out of ideas.
Dave

Re: Tuning the 6 BRA at 600

Reply #25
Did he cut the chamber from a blank or re-chamber?

It sounds like re-chamber to me if there are two angles on the shoulder.

If that is the problem, he might be able to cut the chamber deeper or use a reamer from the initial chamberings to put the two angle shoulder in your sizing die (if the reamer is carbide).

Re: Tuning the 6 BRA at 600

Reply #26
Did he cut the chamber from a blank or re-chamber?

It sounds like re-chamber to me if there are two angles on the shoulder.


If that is the problem, he might be able to cut the chamber deeper or use a reamer from the initial chamberings to put the two angle shoulder in your sizing die (if the reamer is carbide).

Brand new Krieger blank shipped straight from Bruno's to him.
Dave

Re: Tuning the 6 BRA at 600

Reply #27
Again I'm not going to build some goofy two angle sizing die.

Again I hope this is all something I'm doing wrong but can't see how at this point.

If it is a chamber flaw I'm sure he will correct it. If it can't be corrected I'll start over with a new blank and ream this one out to a dasher.
Dave

Re: Tuning the 6 BRA at 600

Reply #28
The only way I see that as a chamber flaw is if a damaged reamer was used.  I want to believe that such would not be the case.  If you are not generating high enough pressures for the neck to seal and you are getting gas blow-by it could cause the shoulder to be depressed as per your pics.  Have they been fired with a full load yet?

Re: Tuning the 6 BRA at 600

Reply #29
Did you verify case length?

I fireform Dasher brass and get sharp shoulders on second firing. Even on a mild charge we’re still talking about tens of thousands of psi. Your brass is (or should be) conforming to your chamber, bump back shoulder from that baseline and I can’t see how it would bind.
What about the body is that getting contacted by the sizing die that you made?
RIP Chris Cornell