Getting the case to seal the chamber with 45-70

C

ckpj99

New member
I've been on a long journey developing 45-70 loads that work well. I started loading for a trapdoor, now I'm loading for a H&R Buffalo Classic.

I love shooting 500 grainers and they are accurate out of the BC. However, since I'm human and made of squishy bits, I keep the loadings relatively light.

I've noticed that my cases have a lot of residue and stuff on them after they are fired. I'm sure this is caused by the pressures not being high enough to seal the brass against the chamber and gases are coming back around the case mouth.

I have a couple of questions about this:

1) Is this a problem to worry about? Specifically, it is extremely unsafe? Is it doing a bunch of damage to my gun?

2) Is there a way to solve this? I've been told annealing might help, but I have no experience with that.

I use mainly Starline and Hornady brass. It doesn't seem to matter. I'm getting a lot of blow back with both type of brass. The entire cartridges aren't covered or anything, but there's big streaks of residue that go back 3/4 the length of the case.

I'm not sure if it matters, but I full-length size by brass and I don't apply a crimp.

Thanks!
 
Your observations are pretty normal with cast bullets and certain powders. Even bumping the powder up may not change anything. A lot of this is from the length of your chamber throat, size of throat, and powder/lube used. I have several 45-70s in different guns and they all shoot great but do this with cast bullets and lighter loads. Even my 357max in my Low Wall does this with light loads. It is perfectly safe, doesn't seem to deter accuracy, and cleans up pretty easily. As far as the cases go, a good tumbling brings them right back to a nice shine. Don't worry about it, it's harmless.
 
Starline (in fact) instructs that their 45-rifle brass must first be annealed when used at lower/traditional-pressure loads.

Not hard.
- Order/use some 750°F Tempilaq
- Use the supplied brush to paint a bit inside each neck
- Let dry a few minutes to a light whitish-green
- Spin the first inch of the case neck in a propane torch until the Tempilaq color - disappears (6-8 sec)
- Drop on towel to cool (no water needed)

This method is entirely predictable/repeatable and accurate.
I recommend not trying shortcuts. 45-rifle brass is expensive. ;)
 
Just to be sure of no misunderstanding or the involuntary appearance of wrong ideas, only the mouth is being annealed; never anywhere near the head (which would be dangerous). Starline only mentions heating the first half inch, but they are heating it too warm by my standards, so doing 3/4 to a whole inch, but using Tempilaq to limit heating, should produce similar results.
 
Why should Starline .45-70 cases first be annealed before loading to reduced loads? I use both Starline and R-P nickle plated cases and have never experienced the residue forming on the case mouths as described by the OP. Firearm is a Marlin lever action and rounds are loaded with 360 gr moly coated cast bullets and a max charge of Trail Boss powder, admittingly two components that would not be routinely found on most loading benches, but separately used for a number of other loadings and turned out to be ideal for the .45-70.
 
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Condor - I think you'd be surprised at the amount of pressure generated by Trail Boss in a 45-70 case.

The loads I use for with 4198 generate around 17,000 CUP. A case full of Trail Boss produces 23,300 CUP with the same bullet. The pressures are perfectly safe in your Marlin, but the velocity to pressure ratio is really weird with Trail Boss.

As NoSecondBest mentioned, using cast bullets can also contribute to the problem.

Does anyone know why cast bullets make a difference? Is it because they fit the bore more tightly and cause more back pressure?
 
Well yes that 23,300 figure is pretty impressive and would certainly make a difference; also explaining perhaps why the rounds don't seem all that wimpish. OK, so Starline is saying that their rifle brass is hard and needs softening to seal with reduced loads. But in my case, post #6, Trail Boss over-powers Starline and I consider all my Trail Boss max loads to be reduced which includes .416 Rem mags and .458 Win mags.
 
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.. residue and stuff on them after they are fired. I'm sure this is caused by the pressures not being high enough to seal the brass against the chamber and gases are coming back around the case mouth.
Click to expand...

This is exactly what is happening, and no, it's not a problem.

it is not a matter of the cases not sealing tight enough against the chamber walls, Forget that, right now. They are sealing just fine.

What you are seeing is not a matter of how tight or how well the cases are sealing against the chamber, but a matter of how long they are sealing.

When the pressure drops, the brass springs back. The bore isstill full of gas under some pressure, (dropping VERY fast) but enough that powder gas flows back around the outside of the case, now that it has sprung back.

It is normal. How much crud forms on the case varies with the caliber, pressure, load, weapon, a great number of factors...

Cast bullets leave more crud, because they are cast bullets. Some lead, and lube is vaporized on firing and adds to the buildup. Jacketed bullets have only powder residue.

High pressure rounds "smash" the brass harder against the chamber, so it takes fractionally longer to spring back, and are usually jacketed bullets so the buildup on the brass is generally less, or less noticed.
 
Why should Starline .45-70 cases first be annealed...?
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Because the cases are telling us they aren't sealing at the pressures used.

Sometimes you do require it. I first discovered this with my 45-90 BP loads and found Starline's instructions to be req'd.
 
What you are seeing is not a matter of how tight or how well the cases are
sealing against the chamber, but a matter of how long they are sealing.
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Don't disagree... BUT.... the necks are not sealing [and/or nor sealing long enough] prcisely because the necks are too "springy" for the pressure/pressure duration.

Annealing solves that problem w/ low(er) pressure loads.
 
the necks are not sealing [and/or nor sealing long enough] prcisely because the necks are too "springy" for the pressure/pressure duration.
Click to expand...

Possibly,...annealing softens the brass, giving back the flexibility lost during work hardening. I don't think annealing makes the brass "more springy", or less springy, what it does is soften the brass so it does not crack when it is worked (by firing and resizing). (edit: PROPER ANNEALING)

And I believe that his cases are sealing properly, otherwise, he would have powder gas blowback into the action, NOT just on the mouth of the cases.

Unlike semi autos, manually operated guns do not yank the case out of the chamber at the earliest practical moment. The fired case sits in the chamber, for a short time to us, but a long time compared to a semi auto, and there is plenty of time (in powder gas terms) for the fired, "sprung back" (unsealed) case to be exposed to gas still floating in the barrel.

Revolver brass often exhibits the same sooty buildup, but to a generally lesser degree, because of the vented barrel (cylinder gap) means more gas escapes, and more dispersion of the remaining gas after the bullet is gone and the pressure drops.

Cases are meant to seal to the chamber long enough for the pressure to drop to safe levels to allow the action to be opened. As long as this happens, they are working "right".

You might reduce the amount of the buildup by different pressure loads, or different powders and bullets, I doubt you can eliminate all of it. Its rare not to get at least a sooty smudge or ring right at the case mouth. Now, if you are getting this all the way, halfway down the case, then something is actually wrong, and needs attention.
 
Your approach to 45-70 loads is different from mine but I want to follow this thread.

I find very practical bullet weights for the 45-70 to be 340 - 360 grains. I hunt in NY so no really big animals for me. I load up and down the power spectrum using both jacketed and my own cast bullets. My go-to powders are H-4895 and Varget.

I have some 500 grain bullets under 42 grains of Reloader #7 - not fun to shoot so I put them in reserve for the marauding elephant that escapes from the zoo hell bent on stomping on people who get in his way. I tried 3031 and 4198 - didn't care for either. I don't like the idea of a low case fill powder where an accidental double charge may not be detected.

I suggest a different bullet and different powder if the blow-back really bothers you.
 
44 Amp,

Below is an annealing chart for brass. Its for a one hour heat soak, so the property changes have more time to occur than they do at case mouth flame annealing temperatures. Thus, what you see happening to properties at 572°F (300°C) on the chart might not happen until 716°F (380°C) with the shorter soak a case mouth gets in a torch flame. You can see, though, that the tensile strength changes with relief of work hardening stress. The yield point (at which the metal goes over from elastic to plastic deformation) goes down with it. This means the stress-relieved brass is a poorer spring, recovering less from bending. What doesn't change is the modulus of elasticity. You still have to have enough pressure to expand it out against the chamber wall whether it is annealed or not. It just won't spring back as much after annealing, so the pressure has to drop to a lower value before it comes away from the chamber wall and starts bleeding gas backward.

Brass%20Annealing_zpso70sv8d4.gif
 
the necks are not sealing [and/or nor sealing long enough]
Click to expand...

We need a graph that shows pressure and time. I became the proud owner of 80 7mm Remington Magnum cases. The cases were given to me by a local reloader. The first thing I wanted to do was talk to the previous owner, that was not going to happen. After that I suggested we talk to the new owner of the rifle, again that was not going to happen.

Problem: I had never seen cases with baked-on carbon around the neck. I had to scrap the necks with a knife blade, nothing else worked. I have no clue how much carbon built up around the chamber neck, releasing the bullet had to be difficult. anyhow, I was going to suggest changing something, whatever he was going was not working, the cases came in a bag, no box with load information.

the first thing I want to happen when the primer is struck is for the case to seal the chamber, others have the benefit of time, they have time for the firing pin to strike the primer, and then? they have the benefit of 'travel time', the case, powder and bullet take off and run to the front of the chamber, and then, the shoulder of the case collides with the shoulder of the chamber. I want my cases to expand and seal the chamber.

and/or nor sealing long enough
Click to expand...
:eek:

F. Guffey
 
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