Brass Life Cycle Study

[Hoot]

Getting back to the original theme of the thread. To reiterate, the new Hornady brass came in varying lengths. Every one was less than 1.70 but greater than the lower spec limit of 1.69 inches. I chose 15 cases as close to the same length as I could find out of the 25. I trimmed .0005-.001 from them to get 15 at 1.6935 inches. Here's the results of the first round of shots. Lengths in red are below Hornady's lower spec limit of 1.69 inches.

see further in thread for latest chart

Interestingly, the more power, the less shrinkage. I suspect this may be due to the higher power cases binding better in the chamber upon ignition. True to task, the lower power loads had the classic soot down one side. The middle and high power loads sealed pretty well. As you can see, over half the cases have fallen out of spec after just one shooting. It will be interesting to see exactly how far our of spec they will become over time. I realize some of you don't give a darn about spec or not as long as they are reloadable, but you have to ask why Hornady made the spec if not to abide by it?

Hoot

[BD1]

On Sunday I cleaned and resized all of my currently dirty brass so I could check them for length. At the end of the process i had 74 hornday factory brass and 88 cut down .284 cases. The results of measuring OAL were interesting.

Hornady Brass:

None of these measured 1.70 when new, so I've never trimmed them.
Average length of the 74 cases was 1.691
Shortest case was 1.685
Longest case was 1.697

Most of this bunch was fired 2 or 3 times, but it did include 21 of the original 25 cases that I'd used for initial load up and testing, (I've sectioned 4 of them). These had been fired 20 times, and all were less than 1.690

Average length of the cases fired 20 times was 1.687.7
shortest of those was 1.685
longest of those was 1.689

Cut down .284 brass:

These are all from the initial batch that I mass produced using a miter saw followed by a cordless drill chucked onto my RCBS case trimmer. All of them have been fired and resized 2 or 3 times.

Average length of the 88 cases was 1.699
Shortest case was 1.696
longest case was 1.703 (I had 3 cases slightly over 1.70 which says something about my margin of error in mass producing these cases)

I was surprised by the number of cases that still measured 1.700 after at least 2 firing/sizing cycles.

In addition to measuring them I looked closely at each case. The Hornady brass all show some evidence of ejector and extractor marks if you look closely. A few of the well used cases show strong extractor marks from heavy cast boolit load testing. You have to look very closely at the .284 brass to find any evidence of extractor or ejector marks, despite the fact that 20 of them were loaded to 40.5 grains of 297 behind the 250 grain FTX, a load that has proved too hot in the hot weather that we've been having, reaching 2300 fps. Fast enough to throw off the ballistic reticule in my Leupy. These results are making me think that the Hornady brass is softer, as well as thinner, than the cut down .284 brass I made. I am now convinced that the .450B cases do get shorter over time as they are fired and resized. Also, the Hornady's start shorter, and shorten faster, than the heavier .284 brass.

BD

[Siringo]

I would have to assume that the design of the 450B case HAS to be thinner and softer to effectively seal the chamber at the manufactures pressure criteria of 35K PSI. My experience with the 284 cases is there is much more sooting than the 450B cases given similar loads and pressures, due to the thicker brass.

Also, if the factory case is fired for the first time, it will end up shorter. As the brass flows to seal the chamber and does not thin due to the low pressures, it would have to become shorter. Resizing may not bring the case back exactly to factory dimensions -- so the original length may not be achieved. I would think that after a while all this would stabilize. Looks like it to me.

[Hoot]

I went to the range yesterday to try some other loads that help reduce the SD's and took another iteration of the life cycle rounds with me. The chart earlier on this page has been updated. You may need to refresh your browser's view of it to flush your cache and see the updates.

Some observations:

Most cases shrunk again, but not as much as they did the first time in. As some have postulated, they may eventually reach equilibrium and resize back to the same point each subsequent cycle.

Shrinkage appears to occur the most with lighter loads, probably related to how well they seal and how tightly they cling to the chamber wall during ignition. They might shrink more at higher loads once they cross the threshold where try as they may, they just can't hang onto the chamber walls. I suspect that is what you see happen when you run them up high enough to cause head imprinting from the ejector and extractor, as witnessed in my first run of .284 fire formed brass. That's why I question Bushmaster choosing to use a chrome lined chamber.

There are rare cases where they defy the above two observations. Could be the metallurgic variations that occur during manufacturing or lack of proper annealing.

I introduced a variable in this process where I used the decapping die sans stem, as opposed to the taper crimp die to get the case mouths to .476 inches. Many rounds exhibited an increase in velocity, a reduction in SD and better groups. In the latter case, some groups though improved, were not stellar because the load just so happens to be a powder step that historically has not yielded a good group with the 225 FTX for my setup. YMMV

The 35 gr load threw my second best group ever for this bullet at 100 yards off of a benchrest!



We've had multiple inches of rain the past few days. It was a humid, foggy, still as a tomb morning. Not even a hint of wind. I was literally swimming in mosquito repellent to keep those buggers off of me and they were still swarming around my eyes. Welcome to early summer in the land of 10,000 lakes.

Hoot

[Hoot]

Here's that latest update

I monkeyed too much with the variables, but learned a little in the process.

I crimped all three runs more with the resizing die (mouth down to .475) to test whether too much neck tension is an oxymoron.
Yes Virginia, you can achieve too much neck tension using the resizing die as a crimp, but it's not a totally bad thing. You just have to adjust your powder charge appropriately. With Lil Gun, I've had some really good accuracy loads but was troubled by the high variations in velocity despite good groups. Now, I'm saying don't worry too much about it. "The proof is in the pudding."

With the 35gr load, I also introduced a narrow stab crimp (Lee FCD) at the lower cannelure. With the 37 and 39gr loads, the additional tension/pressure yielded larger supra-web case swell than I'm comfortable with. No head imprinting though, so they're holding their position at least. That was not the case with Alliant 2400. There, the swell wasn't too bad, but the heads imprinted. I suspect the faster ignition of 2400 gets the case moving before it has had time to bind in the chamber. High pressure is high pressure regardless of how it manifests and it's not smart to make a habit of flirting with it!

Observations:
Higher pressure yielded higher velocity.
Higher pressure tightened up the SD dramatically.
Higher pressure=Higher velocity=Tighter SDs but does not equate tit for tat with better accuracy.
My groups opened up.
In the case of 39gr Lil Gun with the 225 FTX, the cases started to [i]grow back[/b].

Conclusion:
If I pursue this higher neck tension I will do so with lower charges then with just the taper crimp and have to re-workup my accuracy loads.
I will not pursue that in this thread though. It distracts from the original theme. I am going to continue to use the resizer die for crimping. Too many positives not to pursue that. Just don't overdo it without adjusting you charges. That'll be addressed in my "Going the other way" threads for the various bullets.

You may have to refresh your browser's view to flush the cache and see the changes in the chart

[Texas Sheepdawg]

So what would be the shortest tolerable case? I'm just wondering because the Hornady brass I'm using right now has only been fired twice. I bought a box of factory brass and these have only been fired twice. None of them are at or above spec. I am going to measure the rest of the unfired ones later today when I get time.

[wildcatter]

Robin, any length that the firing pin can get at the primer should be ok. But, the shorter the case the less accurate or at least, everything needs to be the same length, if accuracy was your only concern, so what is acceptable, is subjective. The std for the 45acp is no shorter than .010" or you may get a miss fire. Of course far to short can cause pressure problems, as the head space increases, but in this straight case, I've not seen that problem, it either fires or not, it then either hits the target or it doesn't, but if it does, it dies, which is why I said the word "subjective"..

..t

[Texas Sheepdawg]

Robin, any length that the firing pin can get at the primer should be ok. But, the shorter the case the less accurate or at least, everything needs to be the same length, if accuracy was your only concern, so what is acceptable, is subjective. The std for the 45acp is no shorter than .010" or you may get a miss fire. Of course far to short can cause pressure problems, as the head space increases, but in this straight case, I've not seen that problem, it either fires or not, it then either hits the target or it doesn't, but if it does, it dies, which is why I said the word "subjective"..

..t

Thanx Tim. You were exactly the one I was hoping would hop on my question. I will be measuring the remaining 30 cases I haven't used yet and then I will have a baseline. But what is strange, the brass from my Hornady factory loads are closer to spec after being fired, yet they also were averaging very borderline out of spec. Will do more research after I get some sleep.

[Hoot]

Robin, any length that the firing pin can get at the primer should be ok. But, the shorter the case the less accurate or at least, everything needs to be the same length, if accuracy was your only concern, so what is acceptable, is subjective. The std for the 45acp is no shorter than .010" or you may get a miss fire. Of course far to short can cause pressure problems, as the head space increases, but in this straight case, I've not seen that problem, it either fires or not, it then either hits the target or it doesn't, but if it does, it dies, which is why I said the word "subjective"..

..t

Thanx Tim. You were exactly the one I was hoping would hop on my question. I will be measuring the remaining 30 cases I haven't used yet and then I will have a baseline. But what is strange, the brass from my Hornady factory loads are closer to spec after being fired, yet they also were averaging very borderline out of spec. Will do more research after I get some sleep.

The heavier the load and the better the case seals against the chamber walls (less sooting), the less shrinkage you will incur. Factory loads would be a good example of heavier, though certainly not as heavy as many go. When the round is in the chamber and the extraction hook is holding it firmly against the bolt face, you can get away with the case being significantly shorter and still get reliable function. The harder the primer cups are that you use, the more sensitive they seem to be to proper case length. At least that's been my experience. Before I started measuring and sorting my brass by length, some were really short and still worked. I distinctly remember being surprised when I first began measuring for minimum length and found some in the 1.67x range. The good news is that they shrink less after the first initial firing. Also, from my experience, .284 Winchester brass shrink even less than actual 450b brass if you ever go that route. The problem with .284 brass is it seems to vary in thickness from one lot to the next. Some of the ones I bought could not be used without reaming them. BD1 traded me some he bought that work perfect without reaming. Go figure... That's a can of worms in and of itself.

Hoot