Neck bushing, brass spring-back and ideal chamber clearance

[SGK]

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"

 

[PracticalTactical]

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.

 

[SGK]

I can't help but find it partly ironic that over-reducing with a bushing and then expanding with a mandrel is what should be achieved with a (better) expander ball in the resizing die. Maybe dies should have a selection of (redesigned) precision ground expander 'balls' or 'pins'.

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?

 

[stevenpoplin]

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

 

[chromatica]

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.

 

[PracticalTactical]

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.

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.

 

[SGK]

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

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...

 

[stevenpoplin]

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

 

[stevenpoplin]

My bad, not Forster. Redding makes the floating carbide ones
Redding on the right Forster on left

 

[dkhunt14]

How much lower do you go? Thoughts on best starting point for my setup?

You only need to go .001 or .002 below what you want. Then use the correct diameter mandrel. That way your not overworkimg the brass. Matt

 

[dkhunt14]

But the bushing needs to account for brass thickness. Given I have the 21st Century neck turning lathe I already have an expander mandrel of 0.241". So, presumably, as a starting point I should try a bushing of .239 + 2*0.013 = .265"

(Understood re clearance)

Given the amount of working of the brass neck, are you guys lubing the necks ahead of sizing (as opposed to just the case body)? I presume you lightly lube the expander mandrel. Preferred lubricants?

I can't help but find it partly ironic that over-reducing with a bushing and then expanding with a mandrel is what should be achieved with a (better) expander ball in the resizing die. Maybe dies should have a selection of (redesigned) precision ground expander 'balls' or 'pins'.


EDIT: 21st Century says their lathe expander mandrel is "about 0.242".

I dip the case neck in powdered graphite to lube it. Matt

 

[dkhunt14]

But the bushing needs to account for brass thickness. Given I have the 21st Century neck turning lathe I already have an expander mandrel of 0.241". So, presumably, as a starting point I should try a bushing of .239 + 2*0.013 = .265"

(Understood re clearance)

Given the amount of working of the brass neck, are you guys lubing the necks ahead of sizing (as opposed to just the case body)? I presume you lightly lube the expander mandrel. Preferred lubricants?

I can't help but find it partly ironic that over-reducing with a bushing and then expanding with a mandrel is what should be achieved with a (better) expander ball in the resizing die. Maybe dies should have a selection of (redesigned) precision ground expander 'balls' or 'pins'.


EDIT: 21st Century says their lathe expander mandrel is "about 0.242".

Whenever you pull an expander out through the neck, it can move the neck. I get much better run out with a mandrel. Matt

 

[dkhunt14]

I believe guys can over think this stuff, I use a mandrel on virgin brass only.
Measure the OD of a loaded round then subtract the desired amount for a starting point bushing then test both sides to determine what’s ideal rather then targeting a particular setting that your combination may not like. I found that heavier NT shoots more consistently in mine without any annealing.

I agree with heavier neck tensions. Some cartridges like that. But in my tests with using a mandrel verses not, at 1000 yards my vertical got alot better. But I anneal every firing. I bet alot of 1000 yard yard BR guys are using a mandrel. Matt

 

[PracticalTactical]

This seems condescending to me and not necessary at all.

Sorry bud, not my intention

I can describe it here, but you have to be the one to identify with it in practice... or not. Entirely up to you.

 

[dkhunt14]

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

 

[fatelvis]

I think annealing every firing is very important, and helps to eliminate springback, which seems to make for a moving target when sizing is concerned. Annealing would go a long way to making all your sizing attempts more consistent. I was a believer after the first-time annealing, suddenly ALL of my sized brass were much closer in measurement.

 

[dkhunt14]

I think annealing every firing is very important, and helps to eliminate springback, which seems to make for a moving target when sizing is concerned. Annealing would go a long way to making all your sizing attempts more consistent. I was a believer after the first-time annealing, suddenly ALL of my sized brass were much closer in measurement.

I believe it also seals off the chamber better and gives more consistent velocities and bullet releases. Matt

 

[SGK]

I dip the case neck in powdered graphite to lube it. Matt

Whenever you pull an expander out through the neck, it can move the neck. I get much better run out with a mandrel. Matt

I'm using a full length sizing die so I need to lube the side of the case. I don't think a 'wet' lube and a dry lube will mix very well.

Whenever you drive a mandrel through a neck you can move the neck and shoulder. But I will try it.

(I can imagine a more complicated sizing die which does this process while the case is supported within the die. Whether it makes sense to produce such a thing is another story.)

Have you measured the bushing to confirm the number matches the diameter?
Do you anneal?

I got the new bushing from Whidden and it measures much better and now my brass necks are measuring to match the bushing. Silly me for not noticing earlier. It will be interesting to see what difference if any the extra neck tension makes.


The right answer is in there somewhere: (including learning to shoot better)

 

[dkhunt14]

I'm using a full length sizing die so I need to lube the side of the case. I don't think a 'wet' lube and a dry lube will mix very well.

Whenever you drive a mandrel through a neck you can move the neck and shoulder. But I will try it.

(I can imagine a more complicated sizing die which does this process while the case is supported within the die. Whether it makes sense to produce such a thing is another story.)



I got the new bushing from Whidden and it measures much better and now my brass necks are measuring to match the bushing. Silly me for not noticing earlier. It will be interesting to see what difference if any the extra neck tension makes.

I use Imperial to size and size them all. The. I wipe off the lube with a paper towel. I then screw the mandrel in my press and dip the necks in the graphite. Then I th. The mandrel in and wipe off the graphite. I never lube the inside because nothing touches it till the mandrel is ran in. Matt

 

[SGK]

Well yesterday was interesting. When I got the new .267" bushing from Whidden I put my cases back through the die. Now they measured correctly. I figure I have 2-3 thou of neck tension when loading these vs next to nothing previously. (0.243 + 2*0.013 = 0.269 versus a bushing of 0.267".) If you look above 40.8 gr of RL 16 seemed to perform well although the sample size is small (5 shots). I loaded up another 8 rounds at 40.8 gr alongside a similar number at 40.7 and 40.9 and headed back to the range on Friday.

The 40.8 (as well as the 40.7 and 40.9) shot poorly. Average fps 3120.4, SD 14.65, ES 43 (versus the numbers written on the target above). While the sample sizes are very low, statistically (using a T-Test) there's a 93% chance the population averages are different and 86% chance the SD are different - in other words quite high probability of a real change in behavior rather than none. So it seems my rifle doesn't like the neck tension. To be honest I'm a bit surprised how sensitive it appears to be to it.

What's been the experience of others?