Want to get into reloading... where to start?

[TonyD]

RKG - Very good explantion on the physical strains a case goes through during firing. The only thing you left out was that the primer moves rearward and then is reseated as the case is forced back against the breach face.

However, most of the "stretch" (growing in length) is done from full-length sizing. This is why neck-sizing fire formed brass will last much longer. This stretch is greatly reduced by "bumping" the shoulder instead of sizing to SAAMI specs.

 

[Dick]

All this discussion about case stretching got me itching for some real data, so I went downstairs and dug out some .270 Winchester cases that my notes say I'd fired 10 times and trimmed once somewhere along the way. I measured each case carefully with my Mitutoyo digital calibers and then ran them all the way up into a standard RCBS die, lubing only the outside lightly and leaving the inside as is to maximize any potential stretching due to the expander ball. Here's the results for the first 4 cases:

Before After Delta
2.5260 2.5295 .0030
2.5300 2.5340 .0040
2.5280 2.5315 .0035
2.5300 2.5345 .0045
(I'm unable to get the spacing right, but I think that's reasonably clear)

The average "growth" was .0039, and there was so much consistency from case to case that I decided I didn't need to continue. But then I started wondering if it was really the expander ball doing the stretching or simply a result of the case being "squeezed" back to correct dimensions and the brass having nowhere to go but up, so I did another 4 cases after removing the expander ball from the die. Here's what I got:

Before After Delta
2.5265 2.5325 .0060
2.5290 2.5350 .0060
2.5305 2.5360 .0055
2.5225 2.5290 .0065

So, without the expander ball the average increase was .0060, about 50% more than when the expander was used. Interesting, no? I think this demonstrates pretty clearly that dragging the expander back out of the case doesn't have the effect of stretching the case, which is exactly what RKG said. But it raises the question of why the cases sized without then being "expanded" lengthened more than those that had the expander ball dragged back out of them. I can't imagine why that would be the case. BTW (and because I'm guessing that you guys have some knowledge of statistics), I ran a simple t-test and the difference between the means is significant at p<.001, even with such a small sample size.

I'm not in a position to do it right now, but the next interesting thing to do would be to see how much stretch comes from firing, and also from neck-sizing only.

 

[TonyD]

As RKG said, the case will expand to the dimensions of your chamber with obturation being the first expansion in the series. A chamber has natural "stops" - the brass can only expand to the inside dimensions of a reamed chamber with an amount of "rebound" from the elsaticity of the case. Again, as RKG alluded to, how much undersized the case is in relation to the chamber is how much it will expand.

A full length sizing can't squish the case back to it's original dimensions - where would the brass go? It actually reforms the case. The brass is stretched upward to reform the shoulder and neck. A portion of the new shoulder used to be the case wall, and a portion of the new neck used to be the shoulder. The only place it can pull that brass from is what remains below the body of the die - the case head just above the web.

 

[RKG]

WOW all that for a stuck case?

Not quite. In the first instance, unless you can detach the case from the expander, you can't get your die back. After that, it is usually a case (pardon me) of wanting to get the expander button back. Usually this requires sawing the case in two, and even so, there is enough wrong with the case that I'd chuck it anyhow.

Changing the Subject:

Dick's data is fascinating, and I have no ready explanation. Nor, at least intuitively, am I prepared to accept (or reject) TonyD's hypothesis that sizing causes a case length growth because of metal flow (in essence, a form of hollow-tube extrusion).

Here's what someone should do:

From time to time I form cases for a wildcat called .308 x. 1.5" (a/k/a .308 Barnes). This round shares both the head and neck/shoulder dimensions of a .308 Winchester (7.62 x 51), but is shortened to an OAL of 1.5". (Interestingly, it turns out to be the predecessor of the short stubby rounds now considered to be so inherently accurate, but was designed way back in 1961.)

Forming involves setting the neck and shoulder back just a tad over half an inch (if you use .308 brass, which involves a lot of effort; about 0.3" if you start with .300 Savage brass, which works a bit easier). You do this by slowly forcing the .308 (or .300) case into a series of forming dies. When it comes out of the last die, it looks like a stubby .308 with a very long neck.

What I've never done is to measure the OAL of a case that has come out of the last forming die and before it goes into trimming. Based on Dick's data, you would expect this to exceed the starting OAL of the case by a significant amount, and, if so, this might validate TonyD's hypothesis.


I still believe that if you compared the before and after firing case OALs for cases that were neck sized and cases that were full-length sized, you would find a much greater disparity, and this would confirm what the books say, namely that the primary contributer to case stretch with bottle-neck cases is headspace (i.e., case set-back after obturation).

By the way, if the goal of this thread was to keep things at the "basics" level, we have failed quite miserably. Mea culpa.

 

[Adam_MA]

Not quite. In the first instance, unless you can detach the case from the expander, you can't get your die back. After that, it is usually a case (pardon me) of wanting to get the expander button back. Usually this requires sawing the case in two, and even so, there is enough wrong with the case that I'd chuck it anyhow.

WOW that sucks! Guess I'm glad I got the Lee dies. All it takes to get a case free is to losen the collet, and tap it out with a 3/16 punch. I forgot to lube a 308 case and managed to get it all the way up into the die before I realized I grabbed it out of the loading block, and not off the lube pad.

Took me all of 30 seconds to do it, and I was back at it...

Adam

 

[TonyD]

I agree, wat too much info just to say, "Trim, or check, all rifle brass".

However, It's a very interesting discussion and I appreciate everyone's input.

Here's what I just did: I measure 5 cases for cartridge headspace and for COL (trim length). The 5 cases all measured:

x.x59 +/- .0005 for headspace

1.759 +/- .0005 COL

After FL sizing:

x.x56 +/- .0005 (This is what I need for my chamber)

1.766/5 COL

I don't know if this tells us anything but what I see is that by only setting the shoulder back .003" the COL grew by .006.

Adam,

You know I'm no big fan of Lee presses but I use Lee Deluxe rifle dies with excellent results.

 

[Adam_MA]

Adam,

You know I'm no big fan of Lee presses but I use Lee Deluxe rifle dies with excellent results.

Yes I know, and just reading what is involved in removing a stuck case with other dies, I'm glad I got the Lee dies, and will continue to get them for new calibers I start to reload.

 

[RKG]

What it appears to tell us is that the tube extrusion model works, with a factor on the order of 1.0 to 2.0 related to shoulder displacement.

Now, it would be nice to similar data comparing:

Case OAL after all reloading operations other than bullet seating, using cases full length sized,

to

Case OAL after firing in standard chamber, before any case manipulation.

This would give us an order of magnitude indication of the comparative contribution to case stretch of headspace and hollow tube extrusion as a result of sizing.

 

[Dick]

Yes I know, and just reading what is involved in removing a stuck case with other dies, I'm glad I got the Lee dies, and will continue to get them for new calibers I start to reload.

Remember that RKG was describing what you need to do if the case is stuck because the neck expander can't be pulled back out. I've never heard of that happening, and in fact didn't even know it could happen. The more common problem is a stuck case because of inadequate lube on the outside - that's no picnic either, but the recovery procedure is a bit more straightforward and they sell a simple tool for doing it (and I've only had one stuck case in over 30 years).

I've never used Lee rifle dies - do they really allow a simple recovery from a stuck case?

 

[TonyD]

What it appears to tell us is that the tube extrusion model works, with a factor on the order of 1.0 to 2.0 related to shoulder displacement.

Now, it would be nice to similar data comparing:

Case OAL after all reloading operations other than bullet seating, using cases full length sized,

to

Case OAL after firing in standard chamber, before any case manipulation.

This would give us an order of magnitude indication of the comparative contribution to case stretch of headspace and hollow tube extrusion as a result of sizing.

Unfortunately, these cases were not shot in my chamber and I don't have un-sized right now that did come from mine. I have no idea of their dimensions prior to firing or of the chamber they were fired in.

 

[Adam_MA]

I've never used Lee rifle dies - do they really allow a simple recovery from a stuck case?

Yes they are... I just checked their site, and there's even a video demonstrating it...

http://www.leeprecision.com/html/HelpVideos/videos/Case prep/remove stuck case-1.wmv

 

[Dick]

Yes they are... I just checked their site, and there's even a video demonstrating it...

http://www.leeprecision.com/html/HelpVideos/videos/Case prep/remove stuck case-1.wmv

Neat video! Yeah, that's a lot easier than what you need to do with the more conventional style dies.

 

[Adam_MA]

Neat video! Yeah, that's a lot easier than what you need to do with the more conventional style dies.

All of their resizing/decapping dies are designed like that. They do it so you can free a stuck case, but also to make it impossible to break a decapping pin. If the pin runs into unnatural resistance (beridan primed case) the pin just pushes up through the Colet instead of breaking.

 

[highlander]

Good - no, great - explanation. For our new reloaders, I'd just add that lubing the inside of the case neck, usually done with ground mica (inexpensive kits are sold for doing this), can prevent much case stretching during resizing and also make the "upstroke" part of resizing (the neck expansion part) much easier. Any stretch during resizing would presumably come from the thinnest part of the case, i.e., the neck, while stretch during firing comes from just in front of the web, as you described.

Some die companies make carbide expander balls notably Hornandy for RCBS and Redding for there own dies