GC effects on operating pressure

[charger 1]

I often see a company say that a given alloy or hardness is good for such and such a chamber pressure. But then when I look at their loading table I see them using the mixture in an application much higher. For example the lee hardness chart and others say my hardness should limit me to 20,000 +or- yet I know I'm approaching 35,000. Is this because I use GC's. In short are their table listing the pressures for bear back boolits???If so how much does the use of a GC increase the pressure capabilty of a boolit????

[charger 1]

55 views. Nobody knows how much GC's enhance pressure ability? Nobody wants to say? I can't believe in 55 nobody has an opinion

[chunkum]

LOL, OK, Here's my unscientific opinion. It's essentially based on shooting my 45-70 Buffalo Classic. In experimenting with bullets of different hardnesses (i.e. various alloys and cooling tecnniques), I found that a given alloy and hardness in a PB bullet which when pushed over a certain velocity gave "patterns" rather than "groups", but when the same alloy/hardness was used to cast up some GC bullets (two different NEI designs) the results were good groupings at even higher velocities. I haven't done any calculations on this but it's repeatable so I'd say your theory is correct. To just what extent you can push this, I know not. But gas checks do seem to cover a "multitude of sins".
Best Regards,
chunkum

[charger 1]

LOL, OK, Here's my unscientific opinion. It's essentially based on shooting my 45-70 Buffalo Classic. In experimenting with bullets of different hardnesses (i.e. various alloys and cooling tecnniques), I found that a given alloy and hardness in a PB bullet which when pushed over a certain velocity gave "patterns" rather than "groups", but when the same alloy/hardness was used to cast up some GC bullets (two different NEI designs) the results were good groupings at even higher velocities. I haven't done any calculations on this but it's repeatable so I'd say your theory is correct. To just what extent you can push this, I know not. But gas checks do seem to cover a "multitude of sins".
Best Regards,
chunkum

Exactly my finding to. However somewhere out there ,there must be a rule of thumb which utilizes pressure over a given area checked and non checked. Well actually all we want in the increase checked cause I thoroughly believe that the charts are already refering to unchecked

[felix]

Cannot really comment because the loads are different with and without checks. The rule I aways follow is to use a check on a check type of boolit. Granted, using a filler in lieu of a check should work quite well, but I typically don't shoot lead "boattails". I traded off these molds I had years ago, which were never too many anyway. ... felix

[felix]

I think the one sin that is covered with a check is its ability to keep the boolit base round upon barrel exit. ... felix

[sundog]

Felix, yes, but if the base is not good to start with, then you will have a void under the check. A void is a void. Even with the checked variety, that base NEEDS to be as perfect as possible. Just one shooter's humble opinion. You are right though that it at least keeps is round going out of the tube, unless the pressure is so high as to deform it against an improper base.

If you're not getting perfect, or near perfect bases, stop and find out why. sundog

[felix]

That's right, Corky. Must have perfect bases before and after the application of a gas check. The gas check does just that. It checks the gas erosion of the lead upon boolit exit. The obturation goes straight through the gas check and down into the lead, and any off centerness anywhere will be detected and amplified upon exit. ... felix

[9.3X62AL]

Chargar et al--

A lot of good thought so far. Most of my experience relates to handgun applications, less so to rifles.

I think there is an "unintended consequence" of both pressure and the dwell-duration of that pressure that kicks in at about 1200 FPS, whether it's from a rifle or handgun barrel, and that is the velocity threshold at which I start using gas checks. Bear with me here, and all cases assume a well-fitted boolit of similar alloy and use of Javelina Alox lube.

In a handgun barrel, the dwell-duration of the pressure impulse acting on the boolit base is considerably shorter than that of the rifle situation. Let us say that in a revolver or pistol barrel, we require about 25K PSI to get our boolit to the 1200 FPS level, while in the rifle I need about 14K. I use as examples here the 30 Luger pistol and the 32-20 rifle--meaning that both rounds get to the 1200 FPS level with the respective pressures indicated, and that both loads remain accurate and produce zero leading to that velocity. As I exceed 1300 FPS in both calibers with plain-based boolits......lube stars dissipate markedly, accuracy gets squirrely, velocity ES's expand, and a little muzzle leading starts to appear. This at first glance appears to be purely a pressure problem, but I submit that given the pressure level differential between the 30 Luger and 32-20 loads, that DWELL-DURATION OF THE PRESSURE IMPULSE becomes a factor in the longer barrel, even though that impulse starts out lower and presumably dissipates as the boolit travels downbore.

The answer to these issues is the gas check. Use of #311419 in the 30 Luger enables 1450-1500 FPS handily (it's a Ruger--fret not, collectors) and 1800 FPS plus in the Marlin 94, with decent accuracy and zero leading, and pretty good SD's/ES.

This has been my observation, anyway--and is the product of a social science major, so I add caution on that score.

One further point, this from another thread in which Chargar submitted that the use of gas checked boolits might enable my three 32-20 platforms to start reading from the same sheet of music--maybe the gas check is the "great leveler" in a number of ways.

[StarMetal]

....and to think Deputy Al, the 30 Luger usually has a rifling twist of 1 in 9 inches. I bet the 32-20 is no ways near that. To think the 30 Luger is doing those velocities and not leading much and still obtaining some accuracy is more impressive to me then the 32-20.

Joe

[Pilgrim]

The whole subject of lead alloy strength was really discussed by Dave Scovill in a Handloader IIRC. At least he was one of the first to actually try and find out what was going on re: pressure & bullet upset. The shorthand version goes something like this...

Lead alloys will begin upset (obturation) at 1420 psi X BHN. This pressure number was derived emperically by Scovill by using a .45 Colt SAA with the barrel removed. He shot the loads into paper (I think it was) and checked for bullet base upset. I suspect he was using published pressure info and not a piezo electric cell, but don't remember for sure. Anyway, his interest was two fold. First, at what pressure will an undersized bullet expand to fill the chamber in a revolver? And secondly, what will happen to the bullet after leaving the cylinder and entering the barrel? Especially in those instances where the chamber mouth is smaller in diameter than the groove diameter of the barre. The first question has to do with bullet to chamber fit and preventing leading (gas blowby/cutting) in the chamber and forcing cone. The second has to do with bullet upset in the forcing cone and barrel. Again this is to address gas blowby/cutting and thus leading in the barrel. If you think about it a bit, the gas pressure at the muzzle is way down and not very likely to cause any further bullet upset, (AS LONG as the crown is perfect) and I suspect there would be negligible, if any, gas cutting at the muzzle either. Now, let's apply those thoughts to a rifle or other fixed chamber firearm. In this case, bullet upset is only important if the bullet is sufficiently small that it won't fit the throat/leade and will allow gas blowby/gas cutting upon ignition. This is one of the main uses for the GC. It protects the bullet during that initial upset and acceleration down the barrel. It also helps reduce bullet skid during that same interval. Now, here is where the pressure theory really doesn't apply. Once the bullet is fully into the barrel, assuming a cylindrical cross section, where can it distort to? The bullet shape will be held by the constraints of the internal dimensions of the barrel, so BHN really doesn't matter at this point. Within reason, neither does pressure. Where the 1420 X BHN comes into play with fixed chamber firearms is if you are using a bore riding bullet. Now pressure due to acceleration applied to the bullet can cause the bore riding nose to slump/deform, unless it is firmly supported by the lands. That is why bore riders need to engrave .001 or so into the lands to be accurate, and why dimensions of a bore rider are so critical. If you use a bullet like the RCBS 35-200, or similar design, there isn't any bore rider nose to deform, and that is one of the main reasons (IMO) that bullet is so easy to use and get good results. Similar designs also have the same forgiving characteristics as long as chamber fit is OK. Anyway..FWIW Pilgrim

[Bucks Owin]

These are excellent posts. I have a question regarding oversize throats and their effect on pressure....

Let's say one uses an alloy soft enough to upset a .430" bullet to a throat diameter of .432" and then it hits a barrel with a groove dia of .429". Does this violent "resize" have a "double whammy" effect on pressure? (Somewhat like a barrel restriction I guess?)

On the other hand, if one uses a hard alloy of say 50/50 WW and lino, does the initial pressure "bleed past" the bullet while it's in the throat and get reduced by leakage out through the B/C gap? If so, wouldn't this be kinda hard on the gun as far as any "gas cutting" action goes? (Or does this happen too fast to "cut" anything?)
Also, wouldn't this "leakage" result in lower velocities than normal?

Hope I'm understandable here,

Dennis

[9.3X62AL]

Dennis--

I think your question is a case-by-case thing. I try to get a .001"-.0015" step-down at every point of reduction in the revolver--using my 45 Colt as an example, I run .454" boolits into .453" throats that leap into .452" grooves. All this goes out the window if the charge holes don't line up in very close alignment "line of bore/line of chamber", both radial and linear. When you consider all that go haywire in the chamber-to-barrel path of the boolit in a wheelgun, it's a minor epiphany that they shoot as well as they do.

[Pilgrim]

Re: bumping up...The bullet gets bumped up and then swaged back down very quickly and you won't see any pressure bump. At least as far as I am aware. Lead is pretty soft and we are only talking a few thousandths here. The cylinder barrel gap virtually ensures you won't see a bump when the bullet goes into the barrel.

Re: linotype...The situation you describe is a sure recipe for gas cutting in the chamber throat and forcing cone. You would see lots of leading in the cylinder throat and also in the first bit of barrel ahead of the forcing cone. If the bullet was undersized for the barrel as well, I suspect you would see leading due to gas cutting pretty much all the way down the barrel.

One relatively easy way to tell what is going on in your revolver re: leading is where the leading occurs. If it is in the chamber throats, your bullet is too small. If it is in the first part of the barrel, again your bullet is too small and/or too hard and you are getting gas cutting. If your leading is down towards the muzzle of the barrel, your lube is running out/failing you. The above is an over simplification, but it will head you in the right direction re: questions to ask yourself (or this board) if you start to have those kinds of problems. Pilgrim

[charger 1]

According to the tech dept at lee I spoke to today,a gas check typically allows for 170-180% of the fps that would be used without one,given alloy ,lube,cartridge etc are all equal.ie if a load is capable of 1200fps would go to 2000 with a check. I wish he would have talked pressure as they are not one to one. However you dont get one without increasing the other. I( guess the ratio depends on cartridge design

[Bass Ackward]

Charger,

Results are not linear because it depends on so many variables from the caliber, to your reloading techniques to firearm dimensions itself.

I have had ACWW + 2% tin (14BHN) to 3500 fps at about 52,000 psi where my limit was vaporization of the lead to the target with zero leading. I have had ACWW + 2% tin (same 14 BHN) fail at 18,000 and lead in a 44 Mag. Even in the same firearm, with the same load listed above in the 44 Mag, I changed lube and never saw leading again.

So how do you draw up a narrow enough set of variables to be able to answer your question?

[Dale53]

Bass Ackward;
Even with all of the potential problems that cast can cause (I have been one of the lucky ones and have had VERY few problems over the years) they absolutely PALE when comparing to these dern computers (just went through an "interesting" afternoon from just changing my Anti Virus).

Sorry fot the interrupt but the parallel situation just "boiled over":mrgreen: .

Generally, when shooting cast, things go well until that somewhat unpredictable thresold is passed, then, normally, you first get inaccuracy then visible leading. Sometimes, it doesn't happen that way - you just get leading and THEN accuracy goes away.

FWIW
Dale53

[Bass Ackward]

Generally, when shooting cast, things go well until that somewhat unpredictable thresold is passed, then, normally, you first get inaccuracy then visible leading. Sometimes, it doesn't happen that way - you just get leading and THEN accuracy goes away.Dale53


Dale,

Absolutely. The problem is drawing that line with so many variables. And I didn't even mention temperature. One high velocity load I have will shoot MOA at 2600 fps as long as the temperature is 85 df or higher. At 50 or below that load is a 6" performer on it's best days. Veral Smith always said to work up your load on the hottest days at the highest rates of fire expected and you will be good year round. That isn't necessarliy so unless your goal is simply no leading.

Now if I work up the load with solid filler like PSB, then it becomes a year round performer because the plastic takes out the remaining lube and powder fouling left in the bore from the previous bullet firing. This enables me to use any lube that prevents leading at that pressure and velocity and use slow powders that cut pressure but don't burn particularly well .... at any temperature range. Thus, my bullets aren't sized down by the hydrolic action of this tar fouling and maximum engagement of rifling height is possible from bullet to bullet. Translation: No purge fliers. So now all lube has to do is lubricate one bullet only.

[charger 1]

Charger,

Results are not linear because it depends on so many variables from the caliber, to your reloading techniques to firearm dimensions itself.

I have had ACWW + 2% tin (14BHN) to 3500 fps at about 52,000 psi where my limit was vaporization of the lead to the target with zero leading. I have had ACWW + 2% tin (same 14 BHN) fail at 18,000 and lead in a 44 Mag. Even in the same firearm, with the same load listed above in the 44 Mag, I changed lube and never saw leading again.

So how do you draw up a narrow enough set of variables to be able to answer your question?

Well I think I've kinda said that, however there is I think a general consensus we can arrive at,,,,AND I think we can even give it a very approx figure..ie:if we look at extremes,would we say that the max pressure of a GC proj. is the same as that proj. bear back>probably not. Would we say the GC proj is 10 times higher>probably not. So speaking to the issue of variables as I did before they were even raised by using the phrase"all other things being equal" we must be able to come up with a reasonable guestimation as to the diff. in max pressure, one bear one GC'd,ALL OTHER THINGS EQUAL

[felix]

My GUESSTIMATION is 180% improvement in handling peak pressure when using a check on the same boolit design. In other words, I agree with the earlier post which indicates this fudge factor. Pretty much about right as determined by shooting 100-120 yard targets of the same size. ... felix

[Bass Ackward]

My GUESSTIMATION is 180% improvement in handling peak pressure when using a check on the same boolit design. In other words, I agree with the earlier post which indicates this fudge factor. Pretty much about right as determined by shooting 100-120 yard targets of the same size. ... felix


Felix,

I am not going to even ask how you arrived at that figure. :grin:

Charger,

Relax. I am only trying to ensure you understand WHAT you are asking of folks.

In order to do this somewhat scientifically, you would have to ask several people to .... keep "all things" as equal as possible. The more people you could include would increase the statistical accuracy of your information.

Then get everyone to test Liquid Alox with both styles of bullets in a handgun and then a rifle. Then take their results and average them together. I would assume this would be your low test standard.

Next you would have to repeat this with several other lubes .... thought of as a standard because you won't even come close to all. Then average those results together.

Then average all lube results together. If you wanted to be more accurate, you could have this test done 4 times a year to eliminate temperature as a variable.

Then you could roughly achieve what you want with some chance of accuracy. You could then look at several lubes and visually see what lube you may want to use for what application.

But .... could you imagine conducting something of this scale?

Or you can compile some data of value by asking people with experience for input based on what lubes they are using if they apply to a certain metal hardness or standard. That might be of some value. But I just showed you how diverse my results were with ONE metal hardness and you got a little put off because I passed over your all things being equal. My point was that they can never be. Unless you make certain assumptions that negate the question you are asking.

[felix]

BA, off of a car top, shaking with 50 MPH gusts, at 40 degrees, frozen trigger finger, and you have already guessed the rest of the story!!! ... felix

[mike in co]

non technical actual data.
432-255(actual 260+)
2/1 ww/lino h2o quenched no gc is 1330 fps (19.8 aa9)
ww h2o quenched gc 1340 fps (19.5 aa9)

7.5 srh 44 rem mag

note the gas check with less powder makes more velocity.

not sure how big a diff there is in h2o quenched 2/1 to h2o straight ww.

the 2/1 actually shoots better too.

my gun my reloads...ymmv

[charger 1]

Felix,

I am not going to even ask how you arrived at that figure. :grin:

Charger,

Relax. I am only trying to ensure you understand WHAT you are asking of folks.

In order to do this somewhat scientifically, you would have to ask several people to .... keep "all things" as equal as possible. The more people you could include would increase the statistical accuracy of your information.

Then get everyone to test Liquid Alox with both styles of bullets in a handgun and then a rifle. Then take their results and average them together. I would assume this would be your low test standard.

Next you would have to repeat this with several other lubes .... thought of as a standard because you won't even come close to all. Then average those results together.

Then average all lube results together. If you wanted to be more accurate, you could have this test done 4 times a year to eliminate temperature as a variable.

Then you could roughly achieve what you want with some chance of accuracy. You could then look at several lubes and visually see what lube you may want to use for what application.

But .... could you imagine conducting something of this scale?

Or you can compile some data of value by asking people with experience for input based on what lubes they are using if they apply to a certain metal hardness or standard. That might be of some value. But I just showed you how diverse my results were with ONE metal hardness and you got a little put off because I passed over your all things being equal. My point was that they can never be. Unless you make certain assumptions that negate the question you are asking.


True enough. Unless you were looking at the lee or some other chart that converts hardness to pressure levels and said HHHMMMM, I wonder where a good place would be to start if I'm gas checking these[smilie=1: My crude guess from the charts I've seen and people I've talked to at Lee,lyman,hornady etc,has told me that if you started the pressure of a checked boolit OOOHHHH around 1.5-1.7X the pressure of a bear back you would be in the parking lot of the ball park atleast.Multi decades ago this same thing was done if a loader didnt have a certain powder,but had a general rule of thumb that a powder he had was a hair faster. He'd back the grains off a bit and give it a go. I did thousends of times with no ill effects..Many decades later through the use of data bases it is as exact as you describe my idea should be to start. We call them burn rate tables....But years and years ago those and many other concepts just started as GENERAL RULES OF THUMB which were then built on

[Bass Ackward]

Charger,

Elmer Keith's most popular load was 34,000 psi with a 10 BHN bullet using his 250 grain Keith design, 22 grains of 2400 in a 44. And he didn't have the lubes or the slower powders we have today. 1.5 X 34,000 = 51,000 psi, 1.7 X 34,000 = 57,800psi. Personally, .... I would guess these pressures to be a little higher than where I would probably slap on a check. And on some bullet designs, I can't get passed 17,000 psi without a check. No matter how hard they are.

A guy shooting a 222 Remington has to run higher pressures and will need a GC sooner than someone shooting a 22-250 using slower powders. We have guys on this board that have used plastic shot buffers and got 3000 fps out of PB or bare backed bullets in rifles. So any more "I think" of a GC as a .... convienence item, if you don't want to fool with fillers. Or an accuracy enhancer at "any velocity". And there is a lot of wiggle room inbetween those two statements because some guys don't need checks to better my results.

I suspect with the cost of GCs these days you are going to see .... renewed efforts to make PB work. That is once people learn techniques to make / load / shoot them differently from what they are currently doing. So I continue to read this board in hopes they will post their results here.

[BOOM BOOM]

HI,
GREAT THREAD!
In a recient experiment.I have found that I get a lot of leading in the ruger bh 357 when I shoot my gc I80gr bullet w/o the gc . This is with it's gc accuracy load of 4.8 grs of 700X. The gc 160gr bullet does the same. When I use it's accuracy load of 5.2grs of 700x.
Same gun. Same lube.
Yeah, I like to shoot them hot.
But with the cost of gc I will have to cut back RATS!
I expected this to happen but figured I would do the experiment anyway, Hope springs eternal.

[Bucks Owin]

Tomorrow, I'm gonna see if I can dig up some pressure data that I have around here "somewhere" that Speer developed in the early 60's. This was regarding various size lead bullets from around .354" to .362" or so in a .358" barrel. The amazing part was how little difference it makes pressure wise....

Stay tuned,

Dennis

[guninhand]

As luck would have it, I'm on the verge of exploring this problem. I have a SAECO 4 cav .45 gc mold that will only properly take Hornady gc when dead soft pure lead is used. The gc don't go on right with WW alloy no matter what "expanding " trick I use and even if I get them to look good, groups are nauseating.

I will load on a 45 colt case and have 2 handguns and a rifle to try them in.

The question of pressure increase is also a concern to me as the real reason for getting into the pure lead .45 bullets is I have a model 71 Mauser in factory 43 Mauser that has a groove diameter of 0.453 inch. Apparently they must have used a hollow base bullet back in those days. So I need pure lead to load the bullet scheutzen style. The twist is 1 in 28 and I have a plain base 255 to try as well as the Saeco gc 255grainers. I also have a 300 grain RCBS .457 that takes a gc.

I will be sizing to 0.454 in a lee sizer. I plan to use pure lead with the gc designs but already made the plain base ones in traditional scheutzen alloy around 8 BNH. I haven't tried the scheutzen style before this. If I get good accuracy I might have the neck reamed so I can load an assembled round with the ,454 bullets. ( the gun's been "sporterized" )