Brass shrinkage?

[Edward429451]

I've loaded two batches of handloads for my new Guidegun and every single case comes back out of the gun shorter than when it went in.

I trimmed before loading to 2.093 and now their all 2.080-2.085.

I know brass generally grows the most in the sizing die, but never have I seen it get shorter. The loads were mostly starting loads and with a variety of jacketed & cast. What gives?

I've never loaded straightwall rifle cartridges before now so wonder if its a phenomenon unique to them. Plz tell me I'm not nuts.

[felix]

Springback after sizing? Perhaps. ... felix

[versifier]

I don't think you're nuts, but I've never heard of it happening either. My experience is with smaller straight wall cases - .38spec., .357mag, etc. not the bigger .444 or .45-70. I have never measured the lengths of cases before sizing them, only after to see if they need trimming, which is seldom. As I understand it, it's not the firing that lengthens the cases, it's resizing them. Resize the cases, then measure them. If they're still shorter, then something weird is happening that I'd want to figure out, too. Could the chamber be a bit oversize? How do case diameter measurements before and after firing compare? :coffeecom

[StarMetal]

You can't compress metal, you can only move it when trying too. Your cartridge had to be a tad smaller then the chamber in order for it to fit and enter. When you fire it, it expands. In order to expand it has to move metal so it draws metal from other areas. In this case the length. The case gets fatter and shorter. Then you size it. You're squeezing the diameter back down and this makes the case get longer. In your case I think your chamber is alittle on the fat side or your resizing dies is little on the big side, not so big that the resized case won't fit the chamber though. I'd bet that if you had a sizing die that sized those cases down to the exact same size when they were new that they would measure longer then what you are getting now.

Joe

[Four Fingers of Death]

Got any new factory cases? If not get hold of one, preferably the same brand, if it is loaded pull the bullet and compare measurements everywhere. If it is loaded ammo fire one and compare it to the new case. The metals gotta go somewhere, Probably just making the case fatter to fit the chamber as ol' starmetal said. It is an interesting exercise comparing fired cases with new at any time, rells you a lot. To get real accurate base measurements you will have to file down the rims on opposing sides to get the micrometer right on the base, just be careful chambering and unloading it. This will show you where th ebrass is going.

Keep us posted we are always interested in this tricky stuff!

[Edward429451]

Oh I haven't resized the cases yet. A few of them are over max dimensions by the case head and ten of them were with virgin W-W brass. Thats to be expected though before sizing. All my bottleneck brass grows or stays the same length until resized. I never measured my 44 brass after firing (or ever trimmed it for that matter) so it's probably just peculier to the type of brass. I'll resize them tonight and let you know how they came out. Just struck me as odd.

I got pretty leaded up too. I had the dies, Lee mould 457-405F, .457 sizer, and some brass (1F?) given to me when my buddies G-Pa died so figured what more reason to buy a 45/70 do I need?

Anyway, I've been reading a lot about 45/70 lately and it strikes me as odd that the guy was using .457 diameter for cast. If .458 is the nominal diameter, then shouldn't I be sizing to .459 for the cast? Thats prolly why I got leaded up, undersize bullets & gas cutting. Do you think I should just get a 459 sizing die and experiment or is slugging the bore mandatory?

Geez, I'm OT. Maybe I should rename the thread Lets talk 45/70's.

[sundog]

Once upon a time I washed some '06 brass in really hot water, and now I use them in .222 Rem.... http://castboolits.gunloads.com/images/icons/icon10.gif

[powderburnerr]

this problem is showing up a lot with fireformed Black powder cartridges that are being taper crimped or not crimped at all, one of the fixes is to roll crimp the round and that will stretch it back out ,I do not know the reason but do know it happens ,I have a lot of cases that are shorter than when I trimmed then initially , I have stretched a few back out with the roll crimp but give no guarentees . movin brass is movin brass and where it moves from I do not know..................... Dean

[9.3X62AL]

There might be some Topic Nazis in here someplace, but they don't post much. :-)

I tend to agree with Starmetal's observations on brass "shrinkage" or contraction upon firing. I wish I had better science upon which to base that belief, but I've seen it occur with enough straightwall cases--both tapered and parallel sided--to agree with Joe's thesis. Of course, I was a social science major for very good reasons in college--getting past geometry in the math venues was a triumph of massive labor over intrinsic knowledge, I assure you.

Many molds intended for the 45-70 or other 45 caliber rifles produce boolits that fall from the cavities at .457". These might be useful to someone somewhere, but not to me in my rifle. "Sized down and paper-patched" occurred to me to try. The #1 has a .459" throat and groove with .449" lands, 8 rights at 1-20" or thereabouts.

No--hell no. That didn't work in the #1's "Government Ballseat", a very short throat with abrupt rifling leade that efficiently peeled back the paper patches and exposed the bare pure lead .452" cores to the vicissitudes of barrel walls and powder gas blow-by......thus bushing the barrel down to about 36-37 caliber in short order. Real fun to remove, that.

So, all manner of incantations and special methods are required to get my two molds for the 45-70 to drop fatter boolits--temp adjustments, alloy enrichment, contact pouring from well-filled furnace reservoir, those sorts of catechisms. Total PITA. The answer is a MM tool, and that will happen in short order.

[DOUBLEJK]

Edward

Ya might try sizin' fer yer Marlin 45-70 to .460" mine has micro groove n won't shoot cast werth a hoot less thier .460" er even .461"...
Usin' the RCBS 405gr. cast of WW's + 2% tin lubed with Javelina...
42.0gr's Reloader7 CCI200 in Win. cases...gives right at 1670f.p.s.
boolits sized .458" can't keep 5 on a 8-1/2x11" paper at 100yds. n sized 459" they'll do 8" n sized .460" their down to 2-1/2" and sized thru a .461" it never touches the boolit as thier .4605" as cast it'll put 5 in a bit under 2" ifin' I do my part...
My barrel mic's .459"...

[Four Fingers of Death]

What's an MM tool? The answer is probably kno to me and staring me in the face, but its Sunday morning, I'm just out of bed and recently fed a plate of bacon and eggs and my brain ain't ticking over fast enough yet.

[9.3X62AL]

"MM" = "Mountain Molds", specifically a mold producing properly dimensioned boolits. Sorry about that.

[Buckshot]

.............Joe's right on with the case shortening deal. Lay a 6" string out in a straight line (represents one casewall). So it's 6" long right? Now with your finger on the middle of the string pull it out a bit so it's not straight any more (your fired casewall). Measure end to end and it's now like 5.5".

...............Buckshot

[Edward429451]

I measured and resized them all last night. They avg'd .013 shrinkage and then grew an avg of .010 so I guess I'll soon have some 45/70 specials, lol.

Sounds like I should get a .459 sizer and see what happens. My boolits drop from the mould at .460 (ww's) so maybe I can use them as is. Instead of doing the lube melt in a pan thing for them is a .461 sizer die available or would that be a hey Buckshot, wanna make me one deal? ;>)

DoubleJK, thanks for the load info with that 42.0g RX7. I loaded some with 41.0 and some with 42.0 and wondered what they might be doing. (I'm waiting for a new chrony, my old one uh, grew a hole in it somehow.

Are MM's really that good? I just ordered a LYMAN 457643 mould, just for the crimp groove mostly as I found out that Hornady 350's and Rem 405's both have to be seated deeper than the cannelure for proper OAL for my Marlin. Did I screw the pooch by ordering the wrong mould?

[versifier]

I suspect you'll find, if you do diameter comparisons to unfired brass in addition to your length comparisons that the cases are not being sized all the way back to virgin measurements. This is normal for the f/l sizing operation. Even small base sizers don't return them all the way. I think that rather than ending up with .45-70 "specials", you'll find that after the next firing and sizing they will be growing normally again.

[mag_01]

:coffeecom I just loaded some new brass 303 and after firing the cases where shorter----I believe when the case fills out the chamber it pulls the brass back as u describe--- It just happen to me today---case before firing was 2.2125--after firing it was 2.208---case fired again without sizing it-----2.208---I believe brass is pulled in a bit to fill out chamber------Mag_01 [smilie=f: