Casehead Growth Caveat

[Hoot]

"Those who forget the past are condemned to relive it"

I just got painfully reminded of this. You may or may not recall my rant last year about how important it is to check your brass and cull the cases who's heads had grown beyond .5010 as the chamber spec is .5010 and they will resist chambering, possibly getting stuck to where you can't extract them if you force them in. I forgot that and just relived it.

I was preparing my next experiment in the Bartz upper, recreating Texas Sheepdawg's 230 FMJ experiment, other than the steel plate punch. That had already been covered. Not wanting to scar up unscarred brass with stab crimps, I rooted around for some previously stab crimped brass and found a jar of cleaned and processed ones to use. Where I faltered was not paying attention to my own label on the side which read "Resized, CHG (case head growth) 5.010-5.015. I spent the long Minnesota winter going through all my brass and meticulously measuring and binning them by CHG. They sure looked nice from having been resized and cleaned. Before checking your brass for CHG, always resize them first.
Anyway, I made sure all the flash holes were deburred and the primer pockets normalized. I then degreased the first .625 inch depth of the inside of the mouths and the primer pockets as well. Now they were ready for priming. I primed them and sorted them into 5 round ranks by overall case length since one step involved a taper crimp. If you don't grasp why, ask. Anyway, I proceeded to charge the different weights with Lil Gun, then seated the bullets ad finally applied the taper and stab crimps.

Don't they look nice?



As a last test before setting them aside until the next range trip, I decided to "thunk test" some randomly selected rounds. Almost every one made a weak thunk, coming to rest rather quietly. That tripped an alarm and I actually tried chambering them by easing the BCA into battery. No Way Jose. Retracting them was next to impossible as well using the charge handle and took considerable effort. I knew better than to drop the bolt and slam them into the chamber as if I had, I'd still be trying to get them out. Now I get to mount the pulling collet die and pull them all down, to recover the powder. The stab crimp leaves the bullets unusable other than maybe as foulers. 50 bullets, 50 primers and a significant amount of my Sunday all wasted.

What a waste of time and material because I forgot the past. I post this to remind everyone in the hopes that you all avoid making the same mistake. Carefully measure your older brass case heads with an accurate micrometer, not an economy caliper and throw the ones in excess of .5010 into the scrap box, or use them to test stab crimps if you use that method

Hoot

FWIW, most of the cases, which I track how many times they had been reloaded, were in the 4 or 5 reload category. Ones with fewer loads in them, unless you load punishers all the time, usually don't suffer from this as it usually is a cumulative problem.

[Al in Mi]

wasn't there some chatter awhile back on getting some case gauges made?

[Hoot]

wasn't there some chatter awhile back on getting some case gauges made?

Yes, I seem to recall that as well. I could turn my own on the hobby lathe, but I don't trust the carriage feed to hold a half mil tolerance. Better to rough it in and actually use a reamer to finish it. Not that it matters in the long run as I don't mind time spent with micrometer in hand. These would have chambered easily in my original Bushmaster barrel as it was well broke in after 2k plus loads through it. The chamber in the Bartz upper is very precisely cut. Passes .5010 but not .5015 cases.

Newbies, I have a link to a good article on CHG AKA CHE (expansion). I'll see if I can find it.

In the mean time, here's a graphical representation of how/what CHG or CHE is. Its not nearly as distinct a step as depicted in the image, but you can get the idea.

Thanks to Varmint Al, who's web site portion dedicated to the behavior of barrels is a great reference!



Hoot

[Hoot]

Here's a takeaway image of what a stab crimp does to the bullet in order to hang on for dear life:



You can also see the rub from the .476 taper crimp also applied. I didn't run a strain gauge on the press lever, but I'd say most of them took a similar amount of force to pull.

As an act of penitence, I measured the grooves in the pulled bullets. Despite every effort to apply the stabs with equal control, here's the groove spread left behind on them:

.430 = 15
.431 = 26
.432 = 9

If anyone wants those 50 cases, they're yours for the cost of a USPS Small Flat Rate Box. They should work in a chamber with a high round count through it. 1st PM get 'em.

Off to the sack. 04:30 comes early

Hoot

[Al in Mi]

I never would have guessed that Lee die would crimp that deep.

[Hoot]

I never would have guessed that Lee die would crimp that deep.

Al, it's a matter of how deep you crimp the case. It would not need such a severe crimp if the sharpness of the die jaws transferred through the case to produce an equally sharp bite on the bullet. As I said and as you would expect, the sharpness gets diffused transferring through the case. If the bullet had a cannelure or driving band groove. the resistance to indentation would not be a factor as there'd be little to none until the crimp bottomed out. I've stab crimped Barnes XPB bullets and then pulled the cartridge down and you could not see any effect the crimp had upon the bullets structure, despite having an almost squared impression shoved down in the driving band groove.

I experimented once with narrowing the width of the bite on a die. By the time it was narrow enough to produce a clean, succinct impression upon a straight walled bullet without creating an hour glass profile, the bite was almost narrow enough to cut through the case jacket, giving rise to concerns that the case would separate at that point. Looked like someone ran a slightly dull tubing cutter around its circumference. Certainly not a confidence builder to look at it.

Hoot

[Hoot]

I went outside the 9 dots with my resizing setup and was able to recover 40 of the 50 brass that were ever so slightly oversized. 10 were too oversized to recover. I have another batch of 50 ready for the range. Just need some comfortable shooting weather and the ever elusive disposable time. It was hot and humid the past 4 days. We even hit the bunker shortly after midnight Saturday morning as the weather generated a tornado 5 miles due west of me and heading our way. Trashed a few farms and went back up into the cloud as it passed over us thankfully. Some folks East of me are still without power (in this heat) as I write this. Now that we're back to work, the weather man says it will be much nicer.

To go along with the stab crimped FMJs I, through a procedural oversight, made 5 TightNeck ones like reported on several years ago. No picnic coaxing .452 bullets into necks which are only .429 ! I didn't say a minor procedural oversight. Amazingly, with a little finesse, the brass yielded and they seated. No need for a stab crimp on those ones. It may prove interesting to revisit the TNT process as a contrast to stab crimping, though both are extreme measures for achieving good neck tension.

Needless to say, I'll post the results when I have them. The 230 FMJs are a good choice for least expensive 450b reloading, though if you watch the sales and especially the bulk ones at Midway, you can ind the 225 FTX's at prices competitive with the bulk FMJs. I should add to that, at least you used to be able to. With prices ricocheting all over the place, its hard to say anything for sure where reloading prices are concerned. Sure wish my income went up at the same rate as reloading supplies the past few years. the 225 FTX kicks the 230 FMJ's butt in performance, aside from 7/16 steel plate punching.

Stay tuned...

Hoot

[Hoot]

The 230 FMJ outing was a waste of reloading components and a vacation day last Tuesday. 12 different 5-shot runs, so it's taking a while to compile them after work and chores. They didn't group. They patterned, which was the same experience I've had in the past with loading them using my original 450b upper. I have target images to scan and hopefully, I'll get it up in a couple of days. For sure, my next workup will be using a load that's a known good performer in terms of accuracy, as already demonstrated in the Intro article on the Bartz Upper. Bore is breaking in quite nicely. Action still running like a "Swiss Watch". My original 450b barrel took around 200-250 rounds to settle into a long career of good shooting, but it was chromed and that's typically a lot harder than stainless. More to come...

Hoot