Neck bushing, brass spring-back and ideal chamber clearance
- Thread starter SGK
- Start date
There is always a certain amount of spring back but it varies depending upon how far you are sizing. There's literally no such thing as no spring back. It might just be less than you have the ability to measure. But if you pay close attention you can feel it.
If you are sizing a neck down by 0.012" for example, the bend is well past the structural resistance of the brass and you may actually get less spring back than if you were only sizing down 0.004".
If you use a neck only sizing die, you can feel the spring back change based upon this point.
When reducing diameter by 0.012" the case with withdraw from the bushing with almost no resistance, but size a case down in increments of 0.001 or 0.002" and you will have to fight to pull the round back out of the bushing. This illustrates my point.
Progressive sizing in 0.001" increments is also a great way to ensure the side walls are actually parallel. Going in hot and heavy sizing down 0.012" creates a taper in the neck where the mouth is smaller than closer toward the shoulder. Hard to measure, but easy to feel while retracting out of the bushing.
So, I heard more from 21st Century. Their turning arbors are 2 thou under nominal ie .241" for 6mm and their expander mandrels are 1 thou under nominal (0.242" for 6mm). I could try with these (and additional bushings) although it's a bit of a hassle to dismantle the neck turning lathe to get to the turning arbor. I might just order a couple more bushings and a couple of their mandrels. Their caliber specific mandrels have a tolerance of + / - .0002 (Quite useful for practicing correct caliper usage as well.)
My Berger 6mm 105 Hybrid Target would appear to be 0.2425"
My Berger 6mm 105 Hybrid Target would appear to be 0.2425"
21st Century mandrels are Nitrided, does anyone make them in Carbide?
I've had mine made from carbide locally at a carbide cutter grind shop, but it was a personal favor. It would be nice to be able to order them from someone who makes them in production and in tight dimensional increments.
I had two different companies make them for me over the years, but one company had a real old school purist who has since retired. His were dead nuts on size in 0.0002" increments. The second guy wasn't so talented and are not as precise.
I've had mine made from carbide locally at a carbide cutter grind shop, but it was a personal favor. It would be nice to be able to order them from someone who makes them in production and in tight dimensional increments.
I had two different companies make them for me over the years, but one company had a real old school purist who has since retired. His were dead nuts on size in 0.0002" increments. The second guy wasn't so talented and are not as precise.
So Whidden Gunworks - I have their sizing dies - offer "expander balls" in one thou increments. https://www.whiddengunworks.com/product/expander-balls/
Sure they're not in 0.5 thou increments and they're not coated but surely doing contraction and expansion in one go would make a lot of sense. Thoughts?
I have balls. I have Forster balls, RCBS balls, Redding balls, and Whidden balls. I just went through my Whidden dies and I have 6.5 balls, and 338 balls but no 6MM balls or I would mail them to you for free to try.
I abandon the use of balls on all but a couple hunting rifles. Bushings, wilson bushings, not the redding bushings and not the Whidden bushings. work for me in wilson neck dies and redding s type full length bushing die. No garantee any of them are perfect, some id are off by alittle and some not square, but they can be culled. I have not needed to go down the mandrel route, or maybe I just dont know it yet, but probobly a better way than balls. that's my thoughts
I abandon the use of balls on all but a couple hunting rifles. Bushings, wilson bushings, not the redding bushings and not the Whidden bushings. work for me in wilson neck dies and redding s type full length bushing die. No garantee any of them are perfect, some id are off by alittle and some not square, but they can be culled. I have not needed to go down the mandrel route, or maybe I just dont know it yet, but probobly a better way than balls. that's my thoughts
To me your describing increased friction rather than spring back that we self admittedly have trouble measuring at least on the neck mouth and that’s the important spot, Hard to factor something into the equation if I can’t measure or assign a value.
The alloy used by Lapua contains trace amounts of iron. This gives it more spring back than the other (softer) brands of cases. Try using a box of ADG or Alpha brass.
Think about it for a while or better yet go try what I described, then think about it for a while. I can describe it but if that doesn't get the point across, you have to see it for yourself.
The difference is dimensional and what I'm describing illustrates the way metal progressively bends.
Like I stated earlier... using a neck only die, try reducing the neck on just one case by 0.012 and pay attention to how easy it is to retract from the bushing.... Now drop the bushing size by just 0.001 and run it through again... This time will be much harder to retract. Drop it again by 0.001 and try again. Pay attention to the force needed to retract.
Yes there is more friction the second time because there is no longer a taper in the neck. The contact with the bushing is now 100 percent.
There is big juju magic in understanding this. I've been using a variation of this principle for loading competition ammo for 25 years. I've kept quiet about it for a long time watching guys chase their tails over runout and perfect neck tension. The devil is in the details and the case will tell you what it needs, if you pay close attention. One day I'll post a video on it.
Well I guess they're not really balls. I guess for someone to argue for the use of a mandrel after sizing down with a bushing vs sizing down with the same bushing and then extracting this back through the neck they'd either have to have a problem with the shape or its direction of travel. I'm not sure I see much difference...
Some of them are actually balls but not all. still called balls. example is the Forster floating carbide ball.
The issue is with;
the direction of travel
how stable both componants are while pulling that thing up through
limited sizes available
limited materials made from
I have sized cased with a RCBS full length no bushing die that started out pefectly concentric out of the chamber, then still concenrtic out of the die without the ball, and then with the ball and that's when concentricity was lost. Also pulled those balls over a doghnut and things go south too.
Thats not to say concentricity problems can't come from bushings.
One can bush the entire neck or however much of it they want. One can also bush the entire neck a liitle and then however much of the neck theywant a little more.
There are many ways to size a case, I have tried all but Lee collet dies, and mandrels. My prefrence is quality brass, quality dies and bushings, and nothing goes through the neck. For now
The issue is with;
the direction of travel
how stable both componants are while pulling that thing up through
limited sizes available
limited materials made from
I have sized cased with a RCBS full length no bushing die that started out pefectly concentric out of the chamber, then still concenrtic out of the die without the ball, and then with the ball and that's when concentricity was lost. Also pulled those balls over a doghnut and things go south too.
Thats not to say concentricity problems can't come from bushings.
One can bush the entire neck or however much of it they want. One can also bush the entire neck a liitle and then however much of the neck theywant a little more.
There are many ways to size a case, I have tried all but Lee collet dies, and mandrels. My prefrence is quality brass, quality dies and bushings, and nothing goes through the neck. For now
My bad, not Forster. Redding makes the floating carbide ones
Redding on the right Forster on left
Redding on the right Forster on left
This seems condescending to me and not necessary at all.
Matt,
Your probably right and I may have re visit several practices I’ve used at 600 yards that just don’t cut it for 1K shooting. Hopefully I’ll figure it out before I get too damn old.
Jim
I have seen great 600 yard loads, sort of fall apart at 1000. A few years back, one of the better 600 yard shooters came to the WORLD Open. He told me he brought his best two 600 yard guns and he thought that his loads just plain down fell apart. They were both 6mm and he has been dabbling at 1000 some and uses a 30 cal there. I also believe the best 1000 yard load may not be the best for 600. I like to tune my loads at the distance i am competing at. Matt
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