Neck turing 30BR, results
What variation in wall thickness is considered acceptable when preparing 30BR brass?
I'd call that quite good. Two-three times that is "acceptable."
Originally Posted by skeetlee
The linear thermal expansion coefficient of admirality brass is 11.2 microinches per degree. Wonder how much that would affect the cut if the temperature was, say, 10 degrees warmer and there was a little "stacking" of heat on the turner mandrel.
I'm not trying to be a smart alec. I'm asking what the real world affect would be.
I'm fortunate that my "lab" is in my basement where the temperature is within a couple of degrees of 68 year around. Being the paranoid individual that I am, I put my pumpkin in a bucket of cold water between cases.
Not pertinent to this conversation, but the humidity is pretty constant in the basement as well because we run a dehumidifier on a constant setting year around.
Thanks for the reply.
I was getting 0.0002" to 0.0003" on 6PPC; and was pleased.
But my first go at 30BR with the same tool is seeing 0.0010".
I'm doing something wrong and need to figure it out.
fishbone, how are you expanding the necks before turning? -Al
I need to get an old barrel for my Bat in 30BR, I'd like to try the fireform first with 6mm bullets then turn. I am not getting very straight brass out of my expander die. I'm thinking the brass with plenty of runout is causing some turning woes...although my brass turns out good.
Yes, but. What we're trying to measure is the difference, not the exact dimension. I do like carbide mandrels. I will admit I do it the old-fashioned way and turn by hand, so heat buildup is less an issue.
Originally Posted by SGJennings
After one cut, I pull a heavy scotch brite (brown) lengthways on the neck, and make a second pass. I do get .0001 (variance) this way, but as soon as you fire them a couple times, there is enough carbon variation to give up that claim.
One can get too fussy...
> One can get too fussy...
Yah. That's kind of where I was going, just wanted you folks with more experience to carry it along.
Error in the measuring tool, a tad of thermal expansion, in my case a bunch of loose nut behind the butt stock...it all adds up to that last digit on the Mitutoyo not being worth much.
Al, I use the Jim Borden method; expand to 6.5mm, 7mm, then .30 cal. Next, set shoulder back 0.005". Expand on the PMA prep mandrel and then turn. Followed by forming a false shoulder for fire forming.
The few I fired formed with a jump seating and ignoring a cross wind grouped VERY well.
So yes, I may be 'hand wringing' over nothing.
By the way, the PMA tool is great! My problem here is not with their tool. I turned some dead accurate 6PPCs with no problem.
fishbone, when you expand the 6BR necks to .30, the inside of the necks will be funnel-shaped...tapering from the top to the bottom. Making the i.d. of the necks round and straight before turning will give a better fit on the mandrel and less variation in neck o.d.'s after turning. That said, I've never been able to see any on-target difference from cases where I've worked over the neck i.d.'s and ones I haven't. There is a definite improvement the consistency of bullet seating pressure after doing this.
I've been looking at the PMA tool..thanks for the feedback.
Good shootin'. -Al
In fact, one neck turner, TJ Jackson's JACO, was set up to cut a tapered neck. You could adjust that out of the tool's setup, but it isn't how TJ thought best. I don't know if that was TJ's idea, or Ferris Pindell's -- the JACO was modeled on a Pindell design.
Originally Posted by Al Nyhus
That's how I turn my 6PPCs. Not advocating, "just sayin"
Reguardless of how necks are expanded, there will be a slightly tighter area inside where the neck and shoulder meet. This is because
the shoulder gives more support to the neck in that place. It is obviously more work, however I ream the I.D. prior to turning and have no problem making 50 cases and holding 1/10. Can I show this as beneficial on tgt, Nope, I don't shoot that well. To me its just another rock turned over.