Bushing Sizing Question

[Brians356]

brian356,

Are the bushings that gauge considerably tighter coated?

If you mean TiN coated, I mentioned that I found many plain and coated gauged small.

To elaborate, I gauged a total of 17 bushings. Of the 8 TiN coated, all 8 gauged small, of the 9 plain ones 6 gauged small. Of the 17 bushings, only 3 gauged at nominal, and they happen to be plain ones.

My gages are the ubiquitous Vermont Gage class ZZ "Minus", meaning they are .0002" smaller than the nominal size. So if the .279 gage is a snug fit into a .279 bushing, it indicates the bushing is very close to its nominal size. If a .279 bushing will simply not accept a .279 gage, it means the bushing is at least .0002" small. Then if the next lower size gage, .278, is a snug fit, it suggests the bushing is very close to a full .0010" too small; but if it's a looser fit, it suggests the bushing is .0004 to .0009" too small, and it becomes a feel thing to judge where it might fall.

If you happen to have more than one of a particular size bushing (say a plain and a TiN) it's important to always use the same one for a particular load to help ensure consistent neck sizing, as they're not likely to be identical just because they're marked the same size.

 

[Tozguy]

Sheldon, I have encountered the same phenomenon of brass necks resizing smaller than the die or bushing. It seems to be related to the brass not making the sharp bend at the shoulder/neck junction so it continues to swag slightly into the neck cavity of the die or bushing. This can happen because there is nothing in the die that presses the neck brass tight against the die neck or bushing. My guess is that the more resizing required the greater the chances of it happening.

Using an expander is the logical solution. Collet dies don't have this phenomenon.

 

[Brians356]

Sheldon, I have encountered the same phenomenon of brass necks resizing smaller than the die or bushing. It seems to be related to the brass not making the sharp bend at the shoulder/neck junction so it continues to swag slightly into the neck cavity of the die or bushing.

Stopping the neck sizing well short of the neck/shoulder junction would avoid that, wouldn't it? And in practice there's always an unsized portion remaining even with the bushing cranked down as far as it will go. Someone on this forum once stated there is a .050" gap but I'd have to go verify that.

A FL die would have the problem you describe, which seems like the classic "doughnut" unless I am missing something. In any event, seating the bullet short of the bearing surface contacting the tight section, if possible, would obviate the problem.

 

[Sheldon N]

These are both with Redding full length bushing dies, which aren't adjustable as to where the sized portion of the neck starts and stops. I've got the depth set for the proper amount of shoulder bump for each die. On the 280AI the neck is sized about 2/3 of the entire length of the case. On the 308 it sizes pretty much the whole neck stopping just short of the shoulder.

What I'm getting is not a doughnut, the bullet falls freely into a fired case with no issues. Additionally, the sized portion of the neck is consistent in diameter across the entire section contacted by the bushing and there isn't any problem area at the neck/shoulder junction.

I think the issue is exactly what mikecr described, where the soft/annealed brass is being pushed inward at an angle as it goes through the bushing and the resulting size is smaller than the actual diameter of the bushing. The soft brass contributes to the issue with a lack of springback. The larger the amount of sizing accomplished in one step (from fired to final size) the greater the issue... which is why the phenomenon is more pronounced with my 280AI vs the 308.

 

[Brians356]

These are both with Redding full length bushing dies, which aren't adjustable as to where the sized portion of the neck starts and stops.

The sized portion of the neck always starts at the end of the neck, I'm sure you'll agree.

So are you are using a standard Redding "Type S Full Bushing Die"? For those Redding states "The adjustable decapping rod allows you to adjust the bushing position, sizing only part of the neck length when desired." So now I'm even more confused.

 

[Brians356]

What I'm getting is not a doughnut, the bullet falls freely into a fired case with no issues.

"Absence of evidence is not evidence of absence." The bullet falling freely into a fired case doesn't prove there is no doughnut. The chamber neck could be just generous enough to allow the fired neck to expand enough for a doughnut to clear the bullet. And even a very slight doughnut is still a doughnut. (Probably any case reloaded more than a few times but never having been inside neck reamed has a doughnut, however slight and inconsequential it might be. I remain open to reeducation on this assertion.)

 

[Tozguy]

These are both with Redding full length bushing dies, which aren't adjustable as to where the sized portion of the neck starts and stops. I've got the depth set for the proper amount of shoulder bump for each die. On the 280AI the neck is sized about 2/3 of the entire length of the case. On the 308 it sizes pretty much the whole neck stopping just short of the shoulder.

What I'm getting is not a doughnut, the bullet falls freely into a fired case with no issues. Additionally, the sized portion of the neck is consistent in diameter across the entire section contacted by the bushing and there isn't any problem area at the neck/shoulder junction.

I think the issue is exactly what mikecr described, where the soft/annealed brass is being pushed inward at an angle as it goes through the bushing and the resulting size is smaller than the actual diameter of the bushing. The soft brass contributes to the issue with a lack of springback. The larger the amount of sizing accomplished in one step (from fired to final size) the greater the issue... which is why the phenomenon is more pronounced with my 280AI vs the 308.

In support of Sheldon's post, this is an example I encountered recently. When making some 30 Fireball cases out of 223 cases, the shoulder was completely removed from some 223 cases. The chopped case mouth to be resized now is around .363''. A 300 AAC Blackout full length die was used to form the new neck. The die neck i.d. measures .324'' but the necks came out at .319'' o. d.
No expander was used. The cases were annealed before resizing. The necks were formed evenly only smaller than expected.

 

[Brians356]

The die neck i.d. measures .324'' but the necks came out at .319'' o. d.

What tools did you use to measure the bushing I.D. and the neck O.D.?

 

[Sheldon N]

The sized portion of the neck always starts at the end of the neck, I'm sure you'll agree.

So are you are using a standard Redding "Type S Full Bushing Die"? For those Redding states "The adjustable decapping rod allows you to adjust the bushing position, sizing only part of the neck length when desired." So now I'm even more confused.

LOL, you're correct on that. Yes, the sizing starts at the end of the neck. No invisible brass here...

On the Redding dies I guess you're right that I could back the decapping rod out farther to size less of the neck, I hadn't realized they could be used that way. I've always just tightened them down onto the bushing, then backed off 1/4 turn to allow a tiny bit of play for the bushing to float and then secured the retaining ring.

On the doughnut issue, I can't definitively state that I have absolutely "no doughnut". Just trying to say that the issue I'm discussing with bushing sizing has nothing to do with doughnuts at the case neck/shoulder junction.

 

[mikecr]

No, you don't have to neck turn. You're right in your perspective about improving/not increasing runout with expansion.
We should always pre-expand necks prior to bullet seating. This for two reasons:

1. Spring back is counter to last sizing action, and it continues over time(it's not all at once). So if your last action was downsizing, then spring back will be outward and continue outward over time. This is changing tension, causing variance in it, in this case reducing. Where your last action was expansion, spring back will counter inward, increasing tension over time. But the good part in expansion is that it's typically way less than downsizing, so the variance produced in spring back counter is way less than the spring back counter variance after downsizing alone.
I think many come to the conclusion that constant annealing is needed for less tension variance because they have not been pre-expanding necks, thereby leaving necks with a lot of energy remaining to come into balance.
The reason I say this is because my tension remains constant and stable while I rarely anneal.

2. Expansion drives thickness variance outward -away from bullet seating. This reduces loaded runout as measured off seated bullets(what matters). There are tips & tricks to reduce neck misalignment from expander buttons, but I'm sure a separate expander mandrel works better. It's easier. You can get these for expander dies from Sinclair/PMA.

 

[noload]

Mikecr explained my thoughts exactly.

 

[/VH]

No, you don't have to neck turn. You're right in your perspective about improving/not increasing runout with expansion.
We should always pre-expand necks prior to bullet seating. This for two reasons:

1. Spring back is counter to last sizing action, and it continues over time(it's not all at once). So if your last action was downsizing, then spring back will be outward and continue outward over time. This is changing tension, causing variance in it, in this case reducing. Where your last action was expansion, spring back will counter inward, increasing tension over time. But the good part in expansion is that it's typically way less than downsizing, so the variance produced in spring back counter is way less than the spring back counter variance after downsizing alone.
I think many come to the conclusion that constant annealing is needed for less tension variance because they have not been pre-expanding necks, thereby leaving necks with a lot of energy remaining to come into balance.
The reason I say this is because my tension remains constant and stable while I rarely anneal.

2. Expansion drives thickness variance outward -away from bullet seating. This reduces loaded runout as measured off seated bullets(what matters). There are tips & tricks to reduce neck misalignment from expander buttons, but I'm sure a separate expander mandrel works better. It's easier. You can get these for expander dies from Sinclair/PMA.

Expanding with a mantrel, prior to seating is something that I have been considering trying for a while now. Thanks for your thoughts on it. Seems reasonable and the way that you explained it, it sticks better in my head.