Brass Life Cycle Study

[BD1]

Just to be a little more clear; yes, any particular fired straight wall case will be shorter in OAL before it's re-sized, however that same case after re-sizing will generally be a little shorter OAL than it was before it was fired in the first place.

I'm not trying to be pedantic, but I'll put the following out there for the benefit of the guys who haven't be re-loading for long: (it's worth what ya paid for it

It helps me to understand this by thinking about the slight taper that virtually all "straight wall" cases have to help them chamber easily. When fired this taper is blown out to the chamber dimensions releasing the bullet. When you re-size the case you are squeezing that brass cylinder back down to a slight taper by forcing it into a cone shaped die. That action pushes the brass back toward the case head a little bit each time, resulting in a slight shortening.

In a typical bottle neck case the gas pressure against the interior of the case shoulder pushes that shoulder forward until it is stopped by the shoulder of the chamber, and then in the resizing process the neck expander ball is dragged through which also pulls brass forward. These two actions tend to make the brass flow forward into the neck, and the case gets a little longer each time it's fired and re-sized, so trimming is required. Neither of those actions occurs in a "straight wall" case, so there is nothing to counter the compression of the brass toward the head by the sizing die.

Common problems with multiple uses over time in a bottle neck case include head separation caused by the brass being stretched thin just in front of the case head, because that brass moving forward has to come from somewhere, and overly thick case necks caused by the brass flowing into the case neck.

Common problems with multiple uses over time in straight wall cases include case mouth splits from the case mouth being repeated expanded and then squeezed back down, and case OAL becoming too short from repeated resizing.

Brass "flow" from the pressure in the chamber upon firing is something that occurs somewhere in the 60,000 psi and up range, depending on the particular lot of brass. As most straight wall cases operate well below that pressure level, you're not as likely to see this effect. IMHO Straight wall cases eventually die from more simple mechanical forces as a result of being repeated stretched open and squeezed back down during the reloading process.

In the .450B we are adding one more mechanical process with the "body" crimp. It remains to be seen how that effects brass life long term. In the meanwhile, I am getting excellent case life when compared to most bottle necked cases I load for.
BD

[gunnut]

So, It's really begining to look like the brass shrinking is related to the resizing. But, Would this alone account for the diameter expanion of the extractor groove? or would case pressure also be contributing to it?

Interesting side note; We have to specifiy what brass we are using when most other are stuck with what is available

[Hoot]

Only time will tell if the .450B brass will shorten beyond the point of a good firing pin strike. So far, none of mine has. To be honest I haven't checked OAL for a while. The last time I checked they were still all longer than 1.690

Slash, what dies are you using? IMHO it's the sizing that shrinks the OAL of straight wall cases, not the firing.

To be more precise I suppose it's the difference in dimension between your chamber and your sizing die. The more you are moving the brass, the more you will shorten a straight wall case.
BD

That's just the opposite of what I'm experiencing. Mine grow back about .005 after resizing. My guess is my chamber is on the loose side as I get a lot of resizing resistance even with imperial lube. I can just feel them squeezing narrower and longer as I cycle the ram. I gain back another .001 if I cycle it 2 or 3 times, rotating the case a third turn each cycle. It does not exhibit noticeably more or less shrinkage with high versus low power loads. I have recycled two other fellow's once fired brass and no two guns yield brass with the same resizing resistance. Go figure... Makes me want to do a cast of my chamber with some cerrosafe.

No one weighed in with clarification on how the round is supposed to fit into the chamber.

Hoot

My previous post was based upon my observations from this cross-sample back on May 30 of the relationship in length as measured, between 25 unsized and resized brass. Fired from my rifle, 3rd reloading, Hornady brass, Hornady dies. Imperial lube.



I can not explain why mine grow back some length with resizing and BD1's get smaller.

Hoot

[wildcatter]

So Hoot man, let me understand more fully. You're noticing that that cartridges are in spec, after you size them, and then after you fire them, they get shorter, but then you resize the fires shorter cases and after resizing them, they come back into spec??? Am I missing something or is this close to your observations?..t

[BD1]

I think we're missing each other on the way by. Virtually all fired cases are shorter than they were before they were fired, until they are re-sized. The question is: after being re-sized, are they shorter, or longer, than before they were fired. It is the length of the case in a loaded cartridge that is important. In my experience, after repeated firing/reloading cycles, bottle neck cases get longer and need to be trimmed, while straight wall cases get shorter.
BD

[Hoot]

So Hoot man, let me understand more fully. You're noticing that that cartridges are in spec, after you size them, and then after you fire them, they get shorter, but then you resize the fires shorter cases and after resizing them, they come back into spec??? Am I missing something or is this close to your observations?..t

Keep in mind that so far, I have always started out with unsized once fired brass. Only recently have I taken notice of the lengths and started measuring them and the answer to your question is no, they lose a few thousandths each cycle even after resizing them. Kind of like 7 steps backwards and 5 forward.

I think we're missing each other on the way by. Virtually all fired cases are shorter than they were before they were fired, until they are re-sized. The question is: after being re-sized, are they shorter, or longer, than before they were fired. It is the length of the case in a loaded cartridge that is important. In my experience, after repeated firing/reloading cycles, bottle neck cases get longer and need to be trimmed, while straight wall cases get shorter.
BD

OK, now I understand your perspective. In an attempt to shed some light on whether the chicken or the egg comes first? I recently came into some factory new brass and I will be tracking 15 of them through several cycles to quantify their length changes. As I already mentioned, Hornady ships these brass in all kinds of lengths new. Though that's not what I expected to see for brass that goes for a buck a round shipped, it is within their SAAMI spec.

Here's how the factory new brass came in the door.



I will fill in the blanks as we go. What is of particular interest is whether and when the shortest of the new brass falls below 1.690 inches. That would give us a life cycle prediction assuming one cares whether their brass is in spec. I know folks who reload with the attitude that if it goes Kapow and the target goes Whack then all's right with the world. In the case of this particular caliber and rifle, perhaps they are the sane ones and I'm an example of OCD.

Hoot

[gunnut]

Now, This is going to be interesting!
At what point is the case too short to head space and fire?
Yes, A lot of other variable to consider.
Go for it "Hoot"
Keep up the good work!

[Hoot]

I APOLOGIZE BUT I MUST INVALIDATE THESE RESULTS DUE
TO A DISCOVERED TESTING ERROR. EXPLANATION TO FOLLOW
HOOT

OK, chew on this folks.

I prepped 49/50 .284 Winchester brass
1 round sacrificed to procedure R&D
Trim Length 1.70
Rims Reduced from .473 to .467
Extractor Groove left at .409
Flash Holes normalized
Primer Pockets normalized
Mouths Deburred inside and out
Starting mouth ID .435
Expanded to .446 to a depth of .187

Fireform Load Data
Winchester brass
CCI #200 Primers
36gr Lil Gun
Berry TCJ 230gr RN
OAL 2.08
No Crimp Mouth OD .480
All rounds "Thunk" tested



After shooting. Unlike my experience with Hornady brass, there was zero case growth just above the web. Possibly the result of the thicker walls. Possibly the result of just being fired once. You make your own conclusions. FWIW, the Berry's were all over the 4ftx4ft target board at 100 yards. About 15 of the 49 actually hit the target paper I was aiming at. Every round sealed well in the chamber. Not a single one had soot on it. That was a first for me. No rounds needed forward assist to chamber. All rounds extracted after the shot. Mosquitoes were horrendous. Thank God for Cutters.

Hoot

[BD1]

Now we're getting some real info. Good job Hoot! One question; When you trim the .284 brass to 1.70, is this before any expanding or re-sizing? Also, when you measure the resulting length after each cycle, are you measuring before, or after, re-sizing? My interest is in the change in length of the case at that point in each cycle were the case is sized and ready to go back in the press.

I will try and clean some brass and measure it this week. My day off this week was completely occupied by building a little air conditioned pantry in the corner of the garage for my wife. A sacrifice made in the interest of world peace
BD

[Hoot]

Now we're getting some real info. Good job Hoot! One question; When you trim the .284 brass to 1.70, is this before any expanding or re-sizing? Also, when you measure the resulting length after each cycle, are you measuring before, or after, re-sizing? My interest is in the change in length of the case at that point in each cycle were the case is sized and ready to go back in the press.

I will try and clean some brass and measure it this week. My day off this week was completely occupied by building a little air conditioned pantry in the corner of the garage for my wife. A sacrifice made in the interest of world peace
BD

Retaining Domestic Tranquility trumps all other interests indeed.

The 1.70 trim on the .284 cases was done before any resizing. I turned my Lee 450b case trimmer guide down to fit inside the .435 mouths. For the Hornady brass, I use my RCBS Trim Pro, not that I've had to trim any yet, other than even out the high and low points.

My plan is to both measure the before and after resizing lengths in each cycle. Bear in mind, after resizing the .284 brass, my intention is to return to the new Hornady 450b brass for the study. Following the .284 brass through it's life cycle also is a lot of additional work. The only reason I did it at all is that unlike the Hornady brass, the .284s all started out the same 1.70 length. The new Hornady brass, as received, varies quite a bit in initial length. I hope to have some actually loaded up later in the week to start their first pass.

Also, I'm not at all sure I will resize the .284 brass since the mouth ID after firing is already .446. Normally, that is what I would resize fired Hornady 450b brass down to. As long as the .284 brass bases don't increase past .500, do they really need resizing? It's a conundrum because I'd like to regain the lost length by resizing, but I suspect since I did not ream the .284 brass, resizing may squeeze the mouths back down to .435 and then I'd have to once again expand them back to .446 to reload them, working the brass more than necessary. This is an interesting fix to be in, I must confess. I may end up not being able to dodge the reamer after all.

FWIW, oldmanjeffers is to credit for the idea of fire forming as opposed to reaming. It was not my idea.

Hoot