brass question

[swampy308]

I read somewhere of people keeping brass they load lead bullets separate from brass they load with jacketed bullets.
Question is why?

[Wreck-n-Crew]

If your talking rifle loads.....well maybe they are keeping track of how many times they are loading the full power jacketed loads to have an idea of how much life the brass has left.

Then they may be using different brass for precision fmj loads and other brass for plinking cast bullet loads. That may go for pistol or rifle.

[FrankenMauser]

Some people prefer keeping the same lots of brass for the same loads.
Changing lots can cause load variations.

Some people prep brass differently for lead vs jacketed.

Some people "use up" most of the life of the brass for full power jacketed (rifle/revolver) loads before downgrading to light loads with lead bullets.

And, some people are just anal-retentive.

For semi-auto pistols, I don't segregate.
For most revolver and rifle cartridges, I do keep things separate.
Usually, once a lot of brass has been tested for a particular load, that's the load that it gets until I run out of bullets or move on to something else.

[Paul B.]

"I read somewhere of people keeping brass they load lead bullets separate from brass they load with jacketed bullets.
Question is why?"

When a case with a light cast bullet load is fired, the primer pushes the case forward which in turn pushes the shoulder back. After a few loadings the shoulder is pushed back far enough to create an induced head spacing problem. Should one then use that case for a full power load with jacketed bullet, one could easily suffer a case head separation.

Brass used for cast bullet loads can be brought back to proper measurements by using a heavier for caliber cast bullet seating to engage the rifling.

I have a tang safety Ruger M77 in .35 Whelen with a bit too much headspace from the factory, most likely with a Wilson barrel that will case head separate with factory ammo. I loaded up a 100 round batch with the 280 gr.#3589 Lyman cast bullet seated firmly onto the rifling, then set up a separate F/L sizing die to allow that brass to headspace on the shoulder. Can shoot any handload I want in that rifle usuing properly headspaced brass. As I have two other rifles chambered to the Whelen I've decided that Ruger will be a cast bullet gun only.
Paul B.

[Wreck-n-Crew]

I've heard that too Paul. Not sure how much I buy into the theory. Maybe I'm wrong but If headspace was to short allowing enough space and pressure were low enough where the primer won't seal you can have some blow-by when the primer popped out. But the gas cutting on the bolt head would be more of a concern for me on a bolt gun.

Plus there is the danger of a primer coming all the way out and causing some problems. Don't like the thought of that. If you ask me someone's doing something wrong if their reduced loads are too weak pressure wise and/or their headspace was that far off.

I recommend higher pressure in reduced loads and neck size only once fired cases. Pressures around 40,000 on a 30-06, 270 win, etc. will expand the case and the primer won't move far enough back to prevent sealing. At least that's the way I've ran mine with no trouble. Not obvious gas cutting and no shoulder setback either like described. Neck size only and load them again.

Regular loads bump the shoulder back and go with it.


If the pressures are in Normal load ranges and the headspace was too short the case slams back against the bolt as the shoulder pushes back out to fill the chamber. All pressures being equal until the seal around the neck opens up enough for the bullet to release.

[Unclenick]

The setback occurs in all rifle cases. Hatcher measured that a .30-06 case shoulder could be set back by up to 0.006" just by vigorous fast chambering in the Enfield 1917. That would mean the inertia from being thrown forward into the chamber was doing it. Mind you, back then the good match shooters could really work a bolt rapidly. I saw Jeff Cooper demonstrate it on three different visits to the sconce. "Putta-tap". Opened, ejected and closed on the next round.

The key difference in the lead loads is pressure and how quickly the bullet gets moving down the tube. Roughly speaking, if you load to a peak pressure lower than around 30
kpsi, the case never sticks to the chamber wall and winds up backing up to the breech rather than fire-forming to the chamber and stretching at the usual pressure ring location to reach the bolt face. This leaves it small. A heavy bullet jammed in the lands does two things. The jam prevents the firing pin and primer from forcing the shoulder forward, so that what pressure there is, is applied to the forward shoulder, which is the thinnest, and from annealing, often the softest part. The big bullet gets moving slowly so there is a lot of time for the peak pressure to be reached before the bullet has moved much and for the brass to relax a bit into that new shape and be more inclined to take a set and keep it.

I ran into this with jacketed bullets and Trail Boss. I had recommended the powder for fire-forming, but one of the members couldn't get it to work. With some experimentation, I found the bullets had to be heavy, as the ones I'd been using up were. Having them jammed into the lands would raise the peak about another 20% in most instances. So some combination would be fine, too.

[swampy308]

Thanks Paulb that's the information I was looking for.

The only rifle I cast for is my model 94 30-30, and I do keep my brass in same lots.

How will it effect 45acp and 38 special brass, the only way I sort these is by times fired.

[Unclenick]

No effect on either of those cases. The pressure is so low they always just back up in the chamber, rather than stick to it. Because the .45 Auto chamber is slightly tapered, the brass tends to back up, get fatter near the head and shorter. Even after resizing they don't quite fully return to length. With light target loads, I followed some Winchester .45 Auto cases through 50 reloading cycles and found they got shorter an average of half a thousandth of an inch every load cycle. These cases were all about 0.025" shorter by the end of the test.

[tangolima]

Originally Posted by Unclenick

The setback occurs in all rifle cases. Hatcher measured that a .30-06 case shoulder could be set back by up to 0.006" just by vigorous fast chambering in the Enfield 1917.

Whenever shoulder bumping is involved, I need to push on the press lever harder. 10 lb of force or more is quite usual. The ramp force is quite a bit considering the sheer mechanical advantage of a press. It is rather hard to image a brisk working on the bolt handle can set back the shoulder as much as 0.006".

A quick calculation based on conservation of energy shows that one would have to close the bolt in less than 50ms. That's carzy fast, like 20 times per second, nothing short of a semi auto action.

Certainly competition shooters shoot fast, but probably not that fast. What's the fastest mad minute? Less than 40 rounds a minute, if I remember correctly. That's 1.5 sec between shots on the average. True it includes a lot of things other than working the bolt. But 1/10 of 1.5 sec is still 150ms. Much more than 50ms.

Hatcher is undoubtedly a legendary figure when it comes to firearms, but this one I take it with a few grains of salt. It is worth the toiling to bump back shoulder precisely 0.001" in my handloads. I need to believe that to carry on.

-TL

[swampy308]

Thanks unclenick, that's the answer I was hoping for, because I load lead, plated, and jacketed for these, all range brass. I have new brass that I bought for heavy loads.

[Unclenick]

Swampy308,

Glad that put your mind at ease.


Tangolima,

The peak bolt velocity needs only be achieved by the end of the forward closing stroke. Nothing else has to go fast enough. Also, I expect I gave a bad example. The .30-06 is going to be much more prone to this problem than some other cartridges are. And, as an aside, Hatcher's test would have been on new cases whose shoulders were fully annealed and not yet begun work-hardening.

The reason the .30-06 (and other .30-03 derivatives and the 6.5× Swedish) is an older rimless cartridge and these are extra vulnerable to headspace setback is the shoulder angle of the cases are greater than the shoulder angle of their chambers by a small amount. Modern bottleneck cartridges have them the same. These old rimless cartridges are from an era when headspace was measured from the face of the casehead to the junction of the case body and shoulder (aka the shoulder heel), and not to a datum line on the shoulder as they are now. So that corner of the shoulder heel is what the case was supposed to headspace on rather than the whole shoulder surface. The slam forward only had to round the heal a little to get that old headspace measurement to read shorter, and shoving it into the more steeply tapered chamber shoulder, even though the difference is very small, nonetheless would strike the heel alone first, then that's where the change would be measured rather than with a comparator as we do now.

If you look at the old military case dimensions and the chamber dimensions for the Garand, the angle difference is much smaller. I think Garand realized the semi-auto what going to slam the cases home pretty hard and didn't want quite so much difference in those angles to limit the shortening effect.

[tangolima]

Thanks Unclenick for the additional information. I didn't know that the shoulder angle was steeper than the chamber. That could make big difference.

It is indeed the final speed that determines the kinetic energy. I realized that. The work done to set the shoulder by 0.006" was estimated to be 0.67J, based on my experience on resizing. The final bolt speed needs to be 21.4fps to make the kinetic energy.

The bolt starts from stationary. The travel distance is about 6". That requires 47ms, assuming constant acceleration. That's how I derived how fast everything must be.

-TL

[Unclenick]

On reflection, I expect most of the shortening is not from setting the shoulder back as you do in a sizing die, but rather from the head moving forward to expand the body of the case outward to fill the extra width available in the chamber. That will take a good bit less force.

[tangolima]

Perhaps. But I think expanding the body is no easy matter either, consider the thicker and hardened brass.

I do think the different ways of head spacing is more probable explanation. Bumping shoulder during resizing requires quite a bit of efforts (energy). There is nowhere for the brass to go other than extrusion into the neck. This need quite a bit of energy as you can imagine. It would be much easy if there is "vacancy" in the shoulder for the brass to move in.

I still take this with some grains, less perhaps, of salt, at least for now. I will do some experiments to verify.

-TL

[Don Fischer]

Pretty much lost me on this. Low pressure cause's head space problem's? All I've noticed from low pressure is that soot on the case down past the shoulder. I have seen that in cast load's in my 30-06. Low pressure wasn't enough to push the case forward and seal the chamber. Easy fix, just add a bit more powder. I'm thinking a way around that might be using case's that have been neck sized once to much and sizing just enough that it will chamber but you feel the shoulder hit. I would think that that would leave nothing to seal!