Signs of pressure in 45-70

[frumious]

All,

Suppose I decide on a certain brand of bullet, primer, and brass for a 45-70 load. Using a single type of smokeless powder (say, IMR 3031) I can make a 45-70 cartridge that operates at one of three different pressure levels:

• "Trapdoor" Springfield (low-ish pressure)
• Marlin 1895 (medium pressure)
• Ruger No. 1 (high pressure)

So how do I look for signs of pressure when I am working up a load in my Marlin 1895?

Consider a hypothetical Ruger-level load. Will this load flatten primers or expand primer pockets or pierce primers in the Marlin but not in the Ruger? How could that be? I think of these signs of pressure as component failures that predict action failure. But how could the same component fail at one pressure level in one rifle but be OK at that same pressure level in another rifle?

-cls

[SHR970]

In my experience with the Marlins you won't see obvious pressure signs until it's too late...like the bolt lets go on you. In some manuals they call Marlin loads "Full 28K CUP" loads. In others they go to the 40K range since the 444 operates up there and is the same action. Long story short, when you exceed book for Marlin all bets are off as full house Ruger loads are getting into Marlin proof load terriroty.

[bobnob]

I make a habit of staying under book max in my Marlin. Maybe if you used really soft primers you might get a hint but I wouldnt rely on that.

Play it safe. The 45-70 even with middling loads is awesome.

[alank2]

Hi,

Back when I was loading 45/70 for a guide gun I had (I shouldn't have sold it...), I was shooting some 350gr bullets around 1900 fps using VV n133. No pressure signs that I could see, but it was more load than I wanted to get pounded with.

My favorite was the pistol powder loads over at www.gmdr.com

Good luck,

Alan

[SL1]

About the only pressure sign that you can use at all would be the diameter of the pressure ring on the case after firing. That is NOT the same as case head expansion. It is the widest part of the case body, on the case wall above the case head. You need to measure that with a MICROMETER, not a caliper, so that you can get measurements in the ten-thousandths of an inch.

The problem with the method is that it is only a relative measure. The pressure ring depends not just on the pressure of the load, but also on the springiness of the brass, the exact wall thickness of each case, and the size of your particular chamber. And, it will reach a value somewhere in the neighborhood of 45,000 psi (depending on case springiness, etc.) where it will increase at a slower rate than at lower pressures (or maybe even reach a maximum value). So you cannot just keep shooting hotter loads because the pressure ring diameter is not increasing very much.

I have seen some gun writers suggest that you can approximate the pressure of a factory load by measuring the pressure rings of its cases when fired in your gun, then loading your own bullets, primers and powder into the same cases and firing them in the same gun, working-up the powder charge until the pressure ring gets to the factory value. To that I say "maybe."

The real issue is whether the first firing of the case changes its springiness enough to change the relationship between pressure and ring diameter on the next firing. In some "hard" brass cases like Winchesters, maybe not. In some "soft" brass cases like Federal, maybe so. The only way to know about a particular lot of factory cases is to pull bullets from 10 of the factory loads, deprime those cases, and reload each caseTWICE with a load that you can reproduce exactly. If they each produce about the same pressure ring diameter on their first and second firing, then you can use the pressure ring diameter you get from firing the other factgory loads as a goal for your own load work-up. if you cannot get the same results on successive firings, then you cannot rely on this procedure.

Also, remember that the pressure ring is dependent on both the INDIVIDUAL case, and POSITION ON THE CASE. So, you need to keep track of each individual case when you use this method and not compare rings on different cases for different firings. Also, as you measure pressure rings, you will notice that rotating the case in the micrometer anvils will give different readings, maybe varying by as much as 0.001" when you are worrying about 0.0001" differences. I don't think you can get a reproduceable "average" value because it is hard to reproduce the exact position of each "sample" reading of the case diameter. What I have settled on is to rotate the each case and take multiple readings, noting the highest and lowest. I then take the average of the highest and lowest values as the diameter for that case. You will notice that some cases are almost round, while others have a "bulge" area or a "dimple" area. And, the average of the high and low values for each case will differ substantially from case-to-case. So, you really need to pay attention to decide what amount of difference in you loads you can detect with this method. It is easy to fool yourself into believing something that you want to be true. (I also "index" my cartidges in my chambers so that the head stamp is always in the same orientation to guard against the possibility that the chamber is not exactly round, and only use one chamber of a revolver to test-fire cases because there WILL be noticeable differences between chambers in many guns.)

Also, when working-up a load, you need to consider whether repeated firings beyond the first two are changing the brass properties enough to mislead you. I do that by ALSO firing the SAME test load in the first ten cases as many times as I need to fire the other cases to work-up my load.

And, then there is the effect of the temperature at which the loads are fired. You need to try to keep your test firings at about the same temperature, because you WILL see a temperature effect in the pressure ring diameters if you change the temperature by too much. (No, I don't really have a recommendation on how much is "too much.")

Using this method can be quite tedious and requires a lot of cases. If I wanted to know the actual pressure of a favorite load, I would probably send it to White for real pressure testing.

On the other hand, I usually do keep track of pressure ring data when working-up loads for handguns and low-pressure rifle rounds. It is educational and does provide the first indication that something is different than expected. In that sense, if you have some experience with the technique, it is the first good "pressure sign" because it can be used all the way down to the old .45 Colt pressures.

SL1

[flashhole]

SHR 970 is spot on with his comments. The gun is rated at a certain pressure level. In the case of the 45-70, data is supplied for the specific type of gun. Why go beyond what others more qualified than us deem unsafe for the gun?

I shoot the 1895 Guide Gun. 3031 has the potential to go beyond safe loads in that cartridge. Varget is a great powder for the 1895 and you can't put too much powder in the case. H-4895 steps it up a notch but still safe. I get around 1960 fps using H-4895 and 350 grain bullets. I did not find 3031 to be as accurate as the other two powders. Reloader #7 is also a good powder for the 45-70 but has a noticibly sharper raport than the Hodgdon powders.

[Unclenick]

M.L McPherson uses case stretch. Because the locking lug is at the rear of the bolt in the 1895, a good length of metal is between the breech and the lock-up. That means high pressure stretches the steel and allows the bolt face to retreat enough to let the case stretch more than normal. So, cases ejecting suddenly longer would be his sign. I've never need to drive my 1895 that hard, but to each his own.

I keep a list of pressure signs, here.

[totaldla]

Frankly, maxing the 1895 is a mistake. Especially the guide gun.

The best way to do this is (a) believe the load manuals and (b) get your loads pressure tested. Everything else is problematic when dealing with a low pressure cartridge like the 45-70.

Remember, if you want 458WinMag performance - buy one.

[Edward429451]

I notice my brass gets shorter in my Marlin so I must be alright! I agree there is no reason to hot rod the guide gun. Let your shoulder be your guide. If they are pleasant to shoot you are ok. If you can only shoot 10 of them, back off the load.

I hit a Mule Deer with a 400 cast @ 1699 fps and it went down right there like a lightning bolt hit it. It did more damage than I wanted it to to the tenderloin so from then on, I don't elk hunt at the same time as deer. Believe me, you wont need to load hot.

[frumious]

CAUTION: The following post includes loading data beyond currently published maximums for this cartridge. USE AT YOUR OWN RISK. Neither the writer, The Firing Line, nor the staff of TFL assume any liability for any damage or injury resulting from use of this information.


Thanks for all the responses so far, especially those that actually address the question in the OP.

I asked about this because I am starting to work up loads using a different method than I have been using. In a nutshell, the new method involves finding the load that shows signs of over-pressure (working up one cartridge at a time, with about a 1% increase in charge for each cartridge), then working down from there using more normal groups (3 or 5 shots). When working up you will eventually have a cartridge that flattens or blows a primer or something...you know to start your "work down" one increment below that load.

I would like to use this method with my Marlin. But because I figured the bolt would let go (as SHR970 indicated) before I saw any traditional signs of pressure, I have been working up loads in a more-or-less normal fashion...5-shot groups, going up half a grain at a time. Using Starline brass, Hornady 300-grain JHP's, CCI large rifle non-magnum primers, and IMR 3031. I am up to 53.5 grains and my shoulder is OK so far. I figure my shoulder will give out before I hit book max (56.9 grains according to Hornady 7th) but I guess we'll see. If it doesn't give out then I guess I should just stop there and see what I have.

For comparison, using the new method I found that using neck-sized Remington brass, Hornady 168-grain Match bullets, CCI large rifle non-magnum primers, and AA 2520 I can load up to 47.5 grains of powder. This is a full grain beyond the hottest book max I could find. 47.8 causes gas leakage around the primer. This is in my Weatherby Vanguard .308.

I also found that using neck-sized Remington brass, Hornady 40-grain Z-Max bullets, CCI large rifle non-magnum primers, and Varget I can load 42.8 grains of powder. This is 2.8 grains beyond the hottest book max I could find. This is in my Ruger No. 1 .22-250. I could probably push it harder, but I don't have any more room in the case, and I am already using a drop tube. So I will start at 42.8 and work down.

-cls

[SL1]

Frumious,

"Working-down" from charge weights that produce pressure signs may be safe enough in strong guns, where the brass cartridge case or primer cup is the weak link. But, it is not a safe method for guns that can break at lower pressures than will RELIABLY produce recognizable over-pressure signs.

Also, just because an action is used for another, higher pressure cartridge does not indicate that you can load YOUR cartridge to the same PRESSURE.

The issue is the amount of force on the bolt face, which is a function of both the pressure and the SQUARE of the maximum internal diameter of the FIRED case.

As an example, let's consider the .444 Marlin, which is only about .430" inside diameter, while the .45-70 inside diameter is more like .480" (UNFIRED cases). So, assuming for purposes of illustration that those numbers are correct, the difference in force on the action for the same pressure is

(.480/.430)² = 1.246

So, if your gun is also chambered for the .444 Marlin, which has a maximum SAAMI pressure of 44,000 CUP, then the pressure in a .45-70 case that would give the same bolt thrust would be

44,000 CUP / 1.246 = 35,300 CUP

Now, that is a bit higher than the .45.70's SAAMI limit of 28,000 CUP, but it is nothing like 44,000 CUP. So, loading the .45-70 to .444 Marlin pressures might very well damage you gun.

Also, please realize that the numbers I used for illustration are probably NOT accurate enough to calculate the appropriate pressure limit for your gun. Due to the square of the diameter ratio, a little difference in either diameter can have a pretty substantial effect on the bolt thrust ratio.

So, I suggest that you stick with load data that has been approved for the gun you have, rather than try to "wing-it" with calculations like my illustration.

SL1

[flashhole]

Actually the Marlin 1895 lever gun is rated over 40,000 cup. Hodgdon publishes data specific to the lever gun with pressure data right at 40,000 cup but those loads are generally pretty stout and not fun to shoot.

[SL1]

And I find different companies holding the 1895 Marlin to WIDELY different pressure limits for the .45-70 cartridge.

The highest NUMBER that I found was from Barnes, with a stated limit of 42,000 psi. But, they also stated that the SAAMI pressure limit is 28,000 psi, rather than 28,000 CUP. So, it isn't clear to me if they were using CUP or psi for the actual measurements. I also found that Speer is limiting all "modern" .45-70 data to 28,000 psi, and the "Trapdoor" data to more like 20,000 psi. Hornady makes the mistake of saying that the use of the .444 Marlin in the same gun makes it OK to load the .45-70 to 40,000 psi. (But, my exmple in the previous post illustrates why that is not an appropriate basis for 40,000 psi in the .45-70 cartidge.)

Anyway, I can see why the OP is asking questions. The "pros" seem to be all-over-the-map on this particular cartridge/gun combination, and some of the logic that they are providing in print seems questionable, too.

SL1

SL1

[Jim Watson]

AA 2520 I can load up to 47.5 grains of powder. This is a full grain beyond the hottest book max I could find. 47.8 causes gas leakage around the primer.

Scary, Fruminous.
The old rule of thumb, even applied by Speer before they got a real pressure gun, was to load til they saw one "pressure sign" and then reduce by 6%. The point being that when you see any of the usual indications of excess pressure, you were already WELL over the SAAMI specification. A razor edge dividing line of .3 grain means that even though you don't see anything obvious, you are probably considerably over the maximum.

[SL1]

I found that using neck-sized Remington brass, Hornady 168-grain Match bullets, CCI large rifle non-magnum primers, and AA 2520 I can load up to 47.5 grains of powder. This is a full grain beyond the hottest book max I could find.

QuickLOAD with default parameters gives a pressure of 68,100 psi with that load.

Taking out 1 grain of powder gives 63,200 psi. That is still over SAAMI max.

But, those are default values. Your case might be bigger. Is that load compressed in your cases? If so, then you are probably getting pressures something like these. For reference, I set the case capacity to make your 47.5 grain charge just fill the case, and got 62,800 psi. That requied a case capacity of 57.75 grains of water, which is 3% greater than the default value. While that is possible, and the lots of powder may also have different burning characteristics between your canister and the QuickLOAD data, the fact that 0.3 grains more powder makes your primers leak makes me think that your 47.5 grain load really is near 68,000 psi and the 47.8 grain load is near the 69,600 psi that QuickLOAD calculates with default values.

Even if these pressures don't eventually damage your action, they will almost certainly burn-out your barrel throat much more quickly than ammo loaded to the usual pressures.

SL1

[frumious]

SL1, the 47.8 grain charge in the .308 (the one that showed gas leaking around the primer) "just filled the case" when I seated to about 2.815. So the one I am going with has the case just a touch below full.

I am a little concerned about throat erosion and "burning up the barrel" in general (is that just throat erosion?) but I figure the ultra-high-end loads won't be as accurate as the loads that are more like book max or a little below. So I won't be firing enough cartridges at those high levels to do any damage...I will work down past them quickly enough. I plan on firing 25 cartridges per load level as I am not a good enough shot for 1 or 2 groups at a given load level to mean anything.

-cls

[Crosshair]

In my experience with the Marlin 30-30, they develop extraction problems before you get too hot. However that's with the 30-30, no idea about the 45-70

[Unclenick]

SL1,

.45-70 is a funny cartridge in that it's copper crusher and Piezo transducer pressure magnitudes are the same. The old Dr. Lloyd Brownell study shows 30,000 being a number below which the two are about the same in .30-06 loads of at least one component combination, and the at a magnitude of 28,000 for both CUP and psi, the .45-70 is close to that range. The crossover point isn't the same for all cartridges, though, because it's affected by the pressure sample port location. .30 Carbine, for example, is 40,000 CUP/40.000 psi in SAAMI's information. I don't find any other rifle cartridge where they're exactly the same like that, though for the 35 Remington and .444 Marlin the psi numbers are lower than the CUP number, same as with .357 Mag and .44 Mag in pistol (mainly) cartridges.

Originally Posted by frumerious

I am a little concerned about throat erosion and "burning up the barrel" in general (is that just throat erosion?) but I figure the ultra-high-end loads won't be as accurate as the loads that are more like book max or a little below. So I won't be firing enough cartridges at those high levels to do any damage...I will work down past them quickly enough. I plan on firing 25 cartridges per load level as I am not a good enough shot for 1 or 2 groups at a given load level to mean anything.

How hot the loads are depend on as-fireformed water capacity of your cartridges. It also depends on the length of the particular 168 grain match bullet. There are differences between match bullet brands and, in .308 in particular, between capacities of different case brands.

If you read through my pressure signs, you'll find sudden deterioration of accuracy as you increment the charge is one of them. If you have a chronograph, you'll find that at the lower loads (which you can increment about 2% usually in a load work up) will usually give you very close to the same number of feet per second added velocity with each equal increase in charge weight. But if an increase fails to produce the expected velocity increase, it is a sign the metal is stretching and it's time to back down. That should happen in the 1895, too, based on McPherson's test.

Primer punctures and the like are tough indicators to trust as the cup thickness and hardness (plated vs. non-plated, for example) can vary and the shape of your firing pin nose can affect it.

40,000 psi is a commonly given as a Marlin pressure, but McPherson and several others have reported going over 50,000. Garrett ammunition keeps it down to 35,000 psi, and I've always thought that was a reasonable compromise between battering the shooter and performance.

In your .308, Geoffry Kolbe says throats burn out noticeably faster as pressure gets above 58,000 psi, so I don't like to max that chambering out. QuickLOAD suggests you could get the same velocities as you have been with 2520 using Reloader 17, but get there at about 5,000 psi lower peak pressure. It might be a good move to make.

Also, don't forget to put the hot load warning in when you discuss over-published pressure loads.

[HiBC]

This has been pretty much said but I will gel it down a little differently.

The pressure signs you are requesting are warnings that you are dancing on the edge.....with a modern rifle of bolt action strength.

These signs occur at pressure levels well beyond the working pressure level of rifles many other rifle designs.

You might be able to load till you see some pressure signs in a Siamese 98 Mauser 45-70 or in the Ruger #1,though I doubt the 45-70 brass is rated for the sort of pressures that flatten primers,etc.

Your plan is not a good plan.You can do as you choose,but your plan is not good.

I suggest you find out the recomended max operating pressure for a 1895 Marlin in 45-70 then approach that max pressure with due caution.

Years past we did not have so much published pressure data and software like QuickLoad. Your venture is unnecessary.

If I had to guess,this is the result you will get from hotrodding:

The brass supported by the chamber will obturate and grip the chamber.
Some spring will occur with the lockup of the lever action,and the bolt face will move to the rear a few thousandths.

Right at the chamber mouth is where all the stretch of the brass will occur.The brass will thin at a stretch ring.At about the second,maybe third reload you will have weakened brass.

At some point,way up in those high pressures,the case will rip in two,and that hot gas will look for your face.

Or maybe that big bear will need a second shot,but when you jack the action only the rear 3/8 in of the brass will come out,the front part will stay in the chamber and your rifle will not work.