Brass Stretching - Let's Talk

Discussion in 'The Ammo & Reloading Forum' started by Guest, Feb 24, 2003.

  1. Guest

    Guest Guest

    rayra
    V.I.P. Member
    Posts: 92
    (10/3/01 1:23:02 am)
    Reply | Edit | Del All Brass Stretching - Let's Talk
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    Came up in the .45 reloading topic, I'm very interested in what the collective opinion is -

    My understanding is that bottle-necked rifle rounds and high-pressure / Magnum handgun rounds / calibers are most subject to 'stretching' or 'flow' under the pressures of the cartridge firing.
    I've also read more than once that hard crimping is also contributory to this stretching phenomenon, as the tightly-held bullet literally tugs the brass along with it as it tries to leave.

    It's also my understanding that straight-walled carts like .45ACP, and other moderate- to low-pressure loadings (or rounds) don't really have this stretching problem.

    Appreciate everybody's comments, observations, folklore.

    Sign me
    Curious (Rich)

    Xracer
    Moderator
    Posts: 1020
    (10/3/01 9:30:34 am)
    Reply | Edit | Del Re: Brass Stretching - Let's Talk
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    Can't comment on rifle brass, Rich....I haven't realoaded any of that stuff.

    For handgun ammo, however....actually, rimmed straight cases, especially those loaded to high pressure, are the most likely to stretch. For instance, .38 Spl. +P and .357 Mag. should be trimmed to length at each reloading. Even light loads will stretch the cases some.

    Rimless ammo (as used in most auto pistols) headspaces on the case mouth and stretches relatively little. It may balloon just a little, but that's what your die is for.

    For .45ACP, 9mm, and .380ACP, of course I measure the brass before I reload, but seldom have to trim any. 9mm seems to be a bit more prone to stretching than .45 & .380, but not too much.

    Get yourself a good set of calipers, lock it at the recommended case length, and use it as a "go/no go" guage.

    Good Luck......

    rayra
    V.I.P. Member
    Posts: 93
    (10/3/01 3:02:59 pm)
    Reply | Edit | Del Re: Brass Stretching - Let's Talk
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    Thanks Xracer, I've got the case gauges and calipers, I've just never come across a case that was more than a couple thousandths over-length.

    Been reloading for about 15yrs - .45, 9mm, .38/.357, .44/mag, .30-06, .223, .270 - and about the only OL casings I've ever had have apparently been someone else's junk I've picked up out of the dirt at the local outdoor range.
    I'm not anal enough to mark my own brass, just that when a casing fails the gauge, it usually has a headstamp / brand I don't generally use, or more obviously the headstamp is almost wiped out by the flattening of hot loads(which I very rarely use).

    My pistol loads are always 'full house', and a few batches of hot loads once in a while. Same for my rifles, I find a moderate loading that is as accurate as I am ( ) and that operates the weapon properly (Garand and Mini14), and pretty much stick with it.

    And I usually bring home about 85-90% of the brass I took out. I figure 10 trips to the range = 100% loss rate on the brass, effectively making tired or weakened brass Somebody Else's Problem (SEP).

    Anyway, wondering what other's direct experiences have been ( I haven't splurged on a case trimmer, yet).

    Rich

    kdubaz
    Moderator
    Posts: 703
    (10/3/01 3:56:07 pm)
    Reply | Edit | Del Re: Brass Stretching - Let's Talk
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    There are several ways for cases to stretch, Rich -

    Excessive head spacing of rifle cartridges is the most positive way to stretch a case.

    Full length resizing whereas the shoulder of bottleneck cases are pushed back with each reloading will cause the case to stretch.

    Tight crimping of bullets, either rifle or pistol, causes much higher pressures to be attained in the chamber before the bullet starts it's movement down the bore, and this also, causes stretching of cases. Most pistol bullets will have a cannulure or a crimping groove in the bullet body, as some rifle bullets will. A rounded crimp excessively applied here, or a rolled crimp on a tough jacketed bullet with no cannulure will certainly qualify to push the internal case pressures to extreme. A tapered crimp generally won't cause excessive pressure buildup. For cartridges that headspace on the case mouth, the tapered crimp is the way to go. Rolled crimps should only be applied in situations like revolvers, due to recoil, or tubular magazines for rifles. Most box magazine rifles don't really require a crimp to hold the bullets - proper necksizing provide enough friction fit to hold the bullet in place.

    Really hot loadings for handgun and rifle cartridges will cause the stretching, along with enlarged primer pockets. Using moderate loads, my rifle brass, when properly necksized only after fire-forming, will last a dozen or so reloadings. Hot loads reduce this by about 1/2.
    Keep below the ridgeline!
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