Brass Shrinkage With Use

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Brass Shrinkage With Use

Postby Hoot » Sun May 30, 2010 10:40 am

I have seen it mentioned in other posts regarding the fact that unlike bottlenecked cartridges, the brass for the 450b actually shrinks with each use. Due to all the experiments I've been doing, I'm reloading my brass more frequently than I ever thought I would when I got it as once fired brass. Counting that first use before I got them, almost all my brass is now 4th fired and has shrunk. I have not been loading them at the upper limits of their safe pressure, though I'm not sure if that exacerbates the problem. They do grow back a little after resizing, but I'm not sure if that compressing and stretching is good for them.

What constitutes too much shrinkage, AKA Don't use them anymore?

Here's a table of a 25 cartridge sample.

Image

FWIW, I utilized the forum's link built into the post editor to upload the table to an image hosting site.

Hoot
Last edited by Hoot on Sun May 30, 2010 5:31 pm, edited 1 time in total.
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Re: Brass Shrinkage With Use

Postby BayouBob » Sun May 30, 2010 11:09 am

Hoot have you tried the sharp paper clip trick? Where brass stretching is dangerous is just above the rim where it first tapers down to the thickness it remains for the rest of the length of the case. When brass flows it can get a thin spot right there and that can cause case head separation. Take a paper clip or other small piece of thin stiff wire and sharpen one end to a fine point then make an "L" about 1/4" on on the sharp end. Insert the pointed L into the case to the bottom and very slowly pull it up and down while the point is dragging along the inner wall. With the big mouthed 450 case you can even look in it with a pen light while you do it and see what the point is doing. If the point seems to catch on something right at the base of the case wall you could be developing a stretch ring of thinning there. Hope this makes sense.
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Re: Brass Shrinkage With Use

Postby pitted bore » Sun May 30, 2010 4:44 pm

Hoot-
My brass shrinks too. I doubt you have much to worry about. The critical dimension for this brass is the base-to-mouth length; the minimum is 1.690 inches, and the max is 1.700 inches. Your sized brass all falls within those limits. The first place I would expect brass failure to occur would be through fatigue at the mouth of the case. Longitudinal cracks might which might begin to show up there after many loadings and taper crimps. I'd guess the brass will react to repeated sizing like .45 ACP brass, which is known for enduring multiple reloadings. I don't recall any reports of split 450B brass from this forum or the calguns thread, but perhaps I missed them.
Perhaps the others can report on this.
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Re: Brass Shrinkage With Use

Postby pitted bore » Sun May 30, 2010 5:04 pm

BayouBob-
The paper clip trick is a useful one on bottleneck cases. I've got many samples of head separations from my work with 303 British and 7.62x54R reloads. Those cartridges are notorious for head separations. (I've found the RCBS case gauge to be a better indicator of the problem than the paper clip.)

However, I don't think head separations are likely to be a problem with the 450B. Case head stretching and separations are likely to occur when the case stretches upon firing, sort of like pulling taffy. Several conditions can cause this. Such stretching is likely not to happen with a rimless straight case that headspaces on the mouth. Hoot's problem is that the cases shrink in length, rather than stretching, when the cartridges are fired.

It's possible that I'm misinterpreting or overlooking something, of course.

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Re: Brass Shrinkage With Use

Postby Hoot » Sun May 30, 2010 7:15 pm

Each shot / reloading cycle, they shrink a little more and do not recover as far. Hard to say where that lost length is going to. In the cases I've resized, the majority of the resizing effort resides just above the web, but I believe that's just due to the wall being thicker there. Meanwhile, its getting harder to get the same neck tension each subsequent reload without cheating the taper crimp in a little further each pass. I have an inertial puller set up on a pendulous arm that I drop onto concrete from a specific height to gauge the number of strikes it takes to dislodge a specific cartridge. Yeah, I need a life... Anyway, with the once fired brass, I could use a taper crimp of .478 to get a tension that requires 12 inertial puller drops. After 4 reloadings, I now need it set to set the taper crimp to .476 for the same tension. Something's changing...

At the same time, the brass keeps retreating. Here's what I've observed so far:
1 Fire Unsized length = 1.693-95
2 Fire Unsized length = 1.691-92
3 Fire Unsized length = 1.688-90
4 Fire Unsized length = 1.685-87
5 Fire Unsized length = 1.682-84 (that's from a load of 25 brass I just took out of the tumbler this afternoon)
I suspect this last load will no longer resize to a minimum of 1.690, but I haven't tried processing it any further yet.

Bob, I've cross-sectioned a case to actually look at the wall from top to bottom under the stereo microscope. I found no abnormal thin spots.

Up until now, I was mixing my brass together after processing. I d put a micro-dot on the head each time I reload it with one of those push-punches using a reduced strength spring. I had once through fourth fired brass mixed together and I suspect that might be why in some test passes, my SDs were wide. I'm very thorough in my processing and I scale every load. Yeah, I need a life...

If you're new to reloading, here's my step list for the 450b. I keep brass in ziplocs with a sticker on it that has a check-box for each step, so they don't get mixed up.
1: Tumble in clean walnut media (little pieces of dryer sheet mixed in to pick up the dirt and de-static the media)
2: Inspect with a magnifying glass for problems (one of those headband magnifiers from harbor freight)
3: Lube (imperial), decap/resize.
4: Wipe off excessive lube
5: Clean the primer pockets with a cutting uniformer Image(kills two birds with one stone)
6: Uniform the flash holes (one time affair)
7: Lightly burnish inside of necks with stainless steel bore brush in drill (easy does it)
8: 8 minutes in the ultrasonic cleaner (dish liquid/vinegar/water mix) blot, then oven dry
9: Prime, microdot the head to track the number of reloads
10: Measure length segregate by length (new step)
11: Expand/flare mouths (just a hint of the flare)
Note: Lately, I've adopted the the stance of not doing this step and found it yields slightly more tension. Tension is paramount
12: Scale the powder load (I use a Lyman 1200 DPS2, checks perfectly to my beam scale)
13: Seat bullet while DPS2 is dropping next load (the timing's prefect)
14: Taper crimp
15: Optional Lee FCD crimp. The jury is out on this step. Scars the brass with not so obvious benefits so far.

I may have forgotten something. Family is grousing at me to watch a movie with them. Yeah, I need a life...

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Re: Brass Shrinkage With Use

Postby BD1 » Mon May 31, 2010 7:41 am

Most straight wall cases shrink a bit every time they're re-sized. Re-sizing pushes the brass back toward the base and unlike the bottleneck cases firing doesn't move the brass forward much, if at all. The world is full of .45 acp cases that shorter than the minimum length. For the most part they work just fine. Only time will tell what the life span of a .450B case will be, and how short is "too short". Hopefully Remington will get some reasonably priced brass on the market before I find out.
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Re: Brass Shrinkage With Use

Postby gunnut » Mon May 31, 2010 9:11 am

15: Optional Lee FCD crimp. The jury is out on this step. Scars the brass with not so obvious benefits so far.

I Don't think so. The side crimp is the MOST effective crimp. Period. Hands down. It eliminates bullet jump and gets things cooking real good before letting go. If you try to use a tapper crimp with 284 cases you will get a "stuck case" Not fun to clear. The LeGentre side crimp takes care of that.. Chamber any round with a tapper crimp from a mag. factory or reload.Then check the o.a.l.
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Re: Brass Shrinkage With Use

Postby Hoot » Mon May 31, 2010 11:46 am

gunnut wrote:15: Optional Lee FCD crimp. The jury is out on this step. Scars the brass with not so obvious benefits so far.

I Don't think so. The side crimp is the MOST effective crimp. Period. Hands down. It eliminates bullet jump and gets things cooking real good before letting go. If you try to use a tapper crimp with 284 cases you will get a "stuck case" Not fun to clear. The LeGentre side crimp takes care of that.. Chamber any round with a tapper crimp from a mag. factory or reload.Then check the o.a.l.


I will qualify my observation:
As noted in my "225 FTX Going the other way too" thread, I experimented with side crimps. I went from just the taper crimp, to the taper crimp with one standard width Lee FCD crimp on a flat part of the bullet, then two standard width crimps one crimp width apart on the flat part of the bullet and finally two narrow width crimps right on the two cannelures in the 225 FTX. Not much improvement in velocity with any of the side crimps though the velocity SD tightened a little, but in the case of the two narrow width crimps on the cannelures, my 1 inch groups jumped to 2 inches. So, I'm so-so on the side crimp with decent brass and the FTX bullets. I should have been more explicit about my test bed.
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Re: Brass Shrinkage With Use

Postby gunnut » Mon May 31, 2010 1:23 pm

We have a thread for the F.C.D or side crimp. So, I'm going to take W.A.G on the brass shrinkage. I think it could be that your not developing enough pressure to expand the brass and the resizing is shrinking it. Hornady recommends 1.70 max, trim to 1.695. I would assume the .005 is to allow for stretch under normal pressures.
I have had to trim my 45acp brass ever when using moderate loads.
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Re: Brass Shrinkage With Use

Postby oldmanjeffers » Mon May 31, 2010 3:52 pm

Not to get too off topic but how would I get a stuck case with my .284 brass, When all said and done my .284 cases are right their in measurement with factory new loads? ( I run my loaded rounds back through the FL sizing die too rid the case of any heal). I do this very carefully and it takes very little effort/force to run the loaded rounds through again, way less then seating a primmer. I loaded up twenty rounds this way and want to continue but will hold off 'till I get set straight on this. Thanks in advance!
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