Gas Checks and Yield Strength

[Mossy]

First, I'd like to say that I'm astounded by the sheer amount of knowledge and knowledgeable people on this forum. I never knew how much I didn't know about casting. I'd read quite a bit here (and elsewhere) before my first post, and have been reading here for many hours since. Thank you all.

My question is how do GC's effect the BHN*1422 rule for calculating maximum yield strength to determine maximum chamber pressure for working up a high-velocity rifle load?

I don't yet have a hardness tester, but I'm estimating my quenched .285 bullets at 23 BHN. Should I follow the rule and start loading for a pressure around 30K? Or can I bump it up a bit?

[geargnasher]

I know what you're asking, but there isn't a specific answer except what your particular gun, components, and techniques tell you.

I can tell you that the "loading to the yield strength -10%" think is fairly reliable in my experience, but the gas check doesn't add as much pressure/velocity capacity as it does accuracy at rifle velocities. Whatever you do, don't take that formula as a law or get too hung up on it, it's just one way of doing things and often a good place to start, but once you do a lot of experimenting and shooting with a certain gun you'll find it meaningless.

Gear

[RobS]

Whatever you do, don't take that formula as a law or get too hung up on it, it's just one way of doing things and often a good place to start, but once you do a lot of experimenting and shooting with a certain gun you'll find it meaningless.

Gear

Bingo:

There are many more variables to contribute to success of a person's cast boolit shooting endeavors. The only way to know for sure what your gun and components can or can not do is to go out, shoot and see what works best. There are general consensuses to what will yield you more promising results though. It sounds like you have a start but there is powder selection, twist rate, bore condition, boolit design etc. that are all pieces of the puzzle.

[williamwaco]

The .44 Magnum was developed using bullets that registered around 12 BNH.

According to that formula the maximum pressure these bullets could stand would ba around 17,000psi.

I will let you look up what .44 Magnum pressures really are.

Every time I go to the range, my favorite handgun is the .357 Magnum. I load bullets around 11BNH I use a 158 grain plain base SWC over 13 grains of A No 9 or 15 grains 2400.


1422 * 11 = 15,600psi

Again, I will let you lookup the pressure for those loads.

[Mossy]

I realize working up a load is a labor of love. I've spend many months working up a load with J's. This project is going to be tougher. I probably should have started with one of my military rifles in a larger caliber, but before I really began this research I chose my 280 Ackley.

I'm contemplating a load with 3031 and 4895, but I can't shake the foreboding of SEE events I've read about in Ackley's books and elsewhere. Lee's Modern Reloading II claims I can go as low as 50% on the mediums, but even Hodgdon's sheet on reduced loads says to use 60% minimum with the forgiving 4895.

Any thoughts there?

[runfiverun]

4895 will go lower.
fillers such as dacron take the place of case volumn.
for instance i use 24 grs of h-4895 in my 7 mauser and a 145 gr silhouette boolit.
my favorite 308 target load is 28.5 grs I-4895 under a 165 gr bullet, it uses a filer.
other powders such as 2400, 4227, and unique need no fillers.
"the load" [13 grs red dot] is a much used load and requires no filler either, it produces a load with 40k pressure.
so does the 308 load above.
they are just a couple of hundred feet apart in velocity.

[MtGun44]

I regularly shoot .44 and .357 Mag boolits without GCs in the 8 BHN to 12 BHN range at
near full max loads, which violates the "law" apparently. I get no leading, great accuracy
and have no problems. So, don't get too enamored of that BHN and strength
requirement deal.

Bill

[geargnasher]

My point exactly. If you take Elmer Keith's 11 BHN 16:1 alloy, plain-based 429421, and load it per Richard Lee's formula you should limit your loads to just over 14,000 PSI for best accuracy. That's 7 grains of Autocomp at 886 fps according to Hodgdon. So why is it that I can shoot 3" groups at 100 yards with a 4MOA red dot sight using enough 2400 to get me 1360 fps average and the same boolit? Not that the Autocomp load wouldn't do almost as good when loaded to the "pressure limit", but that there are certainly other ways of looking at it.

Gear

[Mossy]

Thank you all for your input. I'm off to load up my first batch of starting loads.

[Bret4207]

First, I'd like to say that I'm astounded by the sheer amount of knowledge and knowledgeable people on this forum. I never knew how much I didn't know about casting. I'd read quite a bit here (and elsewhere) before my first post, and have been reading here for many hours since. Thank you all.

My question is how do GC's effect the BHN*1422 rule for calculating maximum yield strength to determine maximum chamber pressure for working up a high-velocity rifle load?

I don't yet have a hardness tester, but I'm estimating my quenched .285 bullets at 23 BHN. Should I follow the rule and start loading for a pressure around 30K? Or can I bump it up a bit?

Toss that formula stuff and any ideas you have about Bhn being so all fired important out the window. Each gun and load and alloy will react differently. The only real rule is that Fit is King in cast. Start low, see what your gun is telling you and go from there. Ina cast friendly gun you can often equal jacketed speeds, not in a 280 Ackley, but in a 30-30 or 30-40 Krag. In a gun that hates cast, and they do seem to exist, 12-1400 fps might be the limit and even then it might lead.

As to your original question, GC's make things way easier. They still need to fit the gun and they won't cure everything, but they make it easier by a factor or 100 or so as the pressure/fps rise.

[44man]

Throw out the math and stop reading theories. Like gear said, let your gun talk to you.
I have taken PB boolits to over 55,000 PSI in the .454 and shot wonderful 50 yard groups with no leading. Just water dropped WW metal.

[btroj]

44 man, you think the reason you got those groups might be because your revolvers never read the Lee book?

My guns don't care what is supposed to work or what can't work, they just get by doing what they do. I feed them based upon their preferences, not those of any human.

[462]

I'd been casting and shooting boolits, for two-years, before I read of any pressure-determining formulas. Ran the numbers and found that Mr. Keith was correct. So, too, was Bret4207 and his "Fit is King" mantra.

It could be that there are times when the formulas work, or shooters who use them successfully, but that wasn't my experience.

[44man]

44 man, you think the reason you got those groups might be because your revolvers never read the Lee book?

My guns don't care what is supposed to work or what can't work, they just get by doing what they do. I feed them based upon their preferences, not those of any human.
Maybe! [smilie=l: I find so many things wrong in rags and books and would rather listen to anyone here on this site. So many wonderful fellas with actual experience. We don't always agree, it is OK.

[canyon-ghost]

My concern is always the same one. I just pray the bullet mold isn't too oversize and the load low enough to generate heat and pressure. Nothing worse than having a lead bullet drag through the barrel making it hotter than a Texas summer!

I do load development with a very careful, deliberate attitude. There's conditions to fear in it. I've found that some calibers in my guns need a medium-fast load to be accurate and some need a minimal load.

I start with five different loads from starting load to 4/10ths higher. I use 1/10th grain increments shot at a quarter spot (usually on poster board). Meaning that, to do a 2 grain powder range, there's 20 seperate targets and 100 rounds! Five shot groups at a small dot, whichever shoots the tightest group wins- no compromise in most cases. And I may take more than a few weekends to do all that and digest the findings. A good load can run from slow and soft to medium hot (I choose powders based on accuracy and bulk, mostly).

When all this goes on, I'm in my thought zone. I'm calm, relaxed and patiently waiting for the answer that lets me load 100 or 500 rounds of good, consistent ammunition.

What the formulas didn't tell me: My 41 magnum New Model Blackhawk has a tighter bore and only likes a particular bullet mold, it shows 1315 fps across a chronograph where, the book says it only gets 1150 fps.

My 7mmTCU handgun detested a bore ride bullet mold, and favored a Lyman gas check mold ten grains lighter in weight. This one likes water quenched for velocity. It's a wildcat.

The 32 mag was a neat little revolver, lower the load and pressure and heat show up, too much and the little action takes a beating.

So, to what I'm saying- You may have to change bullet molds to get it to work, may have to change powders yet. Might have to experiment with sizing, gas checks, etc. Take your time.

Personally, I think your bullets at 23 bhn are quite hard enough if, only if, the firearm likes the particular bullet design. Gas checks do a lot by moving the force of the blast forward onto the driving bands rather than the base. This is all in elasticity of lead. It causes the middle driving bands to swell from the impact on the base rather than, causing the base to swell, dish out, or gas cut. I dislike the vague idea that they scrape the lead out of the bore, I think they do a lot toward never letting it start, in the first place.

Good Luck,
Ron

[mdi]

Toss that formula stuff and any ideas you have about Bhn being so all fired important out the window. Each gun and load and alloy will react differently. The only real rule is that Fit is King in cast. Start low, see what your gun is telling you and go from there. Ina cast friendly gun you can often equal jacketed speeds, not in a 280 Ackley, but in a 30-30 or 30-40 Krag. In a gun that hates cast, and they do seem to exist, 12-1400 fps might be the limit and even then it might lead.

As to your original question, GC's make things way easier. They still need to fit the gun and they won't cure everything, but they make it easier by a factor or 100 or so as the pressure/fps rise.
I was waiting for someone to say this, thanks Bret. I experienced leading with my cast reloads until I learned that fit is prolly the most single important factor in shooting lead bullets. I don't have the experience that many have here, so I was/am hesitant to speak up at times...

[Larry Gibson]

The problem with the formula(S) using psi is they only use the base figure and do not consider or take into account the actual time/pressure curve. Take the 44 Magnum under discusion: the "yeild strength" of a cast bullet will be much lower with a MAP of 35,000 psi reached with Unique than with H110/296. The Unique load will reach the 35K psi much quicker.

The use of GCs (of proper thickness and hardness) also allow for a softer alloy to maintain accuracy at a higher psi because the base of the bullet is protected from adverse setback/obturation and remains square the bore on muzzle exit. This is why I always recommend GC'd cast bullets for use in magnum level handgun loads with softer alloys and in rifles with velocities over 1500-1600 fps.

Larry Gibson

[geargnasher]

Pressure is pressure, and yield strength is yield strength, although 100 joules applied with a flyswatter is a different kind of force than the same force applied with a vise.

Manipulating the time/pressure curve is how one far exceeds the BHN/PSI theory, as well as manipulating the malleability and elasticity of alloys.

However, pressure is still pressure, and if you load to 10% under the ultimate compressive strength of the alloy, the load is decently balanced, and the boolit fits, you will likely be very close to a good accuracy window regardless of whether you used Bullseye or 2400.. Pressure is pressure, whether it peaks just as the boolit breaks static friction with the case neck or two inches later. The inertia of the boolit and how it skids when the rifling grabs it and yanks it into a spin is affected greatly by powder burn rate at a given pressure, and many other factors too of course, but if you're talking strictly peak pressure, ultimate compressive strength, and accuracy, the BHN/PSI formula is pretty predictable, and pretty good.

The reason I always bring this up in these discussions is that the BHN/PSI formula has a place, although it's NOT for the fellow who's been reloading, casting, and shooting every day for 60 years, or the man who has 300 guns in his aresenal and a large percentage of them fitted with strain gauges. It isn't for me, either, most of the time, although, like many other things, I took time to learn the Lee way of loading to the alloy strength to see how it worked in almost all of my guns and, lo and behold, it worked pretty well if you don't mind being stuck at the bottom of the performance spectrum. It's a quick-and-dirty road to pretty good success with average cast boolits and average reloading equipment for folks that don't know a lot about the nuances of shooting cast boolits. It also makes powder selection far less critical, something very important for a beginning hobbiest with a small selection of powders on hand.

Gear

[runfiverun]

it is a way of doing things.
we all have a little bit different way of doing things to get to the same goal though.
i rely on luck and guessing to make my guns shoot cast.
others rely on experience, previous note taking.
some look for certain things in a gun and load to match those indicators.
and some rely on testing.

[Larry Gibson]

"regardless of whether you used Bullseye or 2400.. Pressure is pressure, whether it peaks just as the boolit breaks static friction with the case neck or two inches later. The inertia of the boolit and how it skids when the rifling grabs it and yanks it into a spin is affected greatly by powder burn rate at a given pressure, and many other factors too of course, but if you're talking strictly peak pressure, ultimate compressive strength, and accuracy, the BHN/PSI formula is pretty predictable, and pretty good."

At one time I would have agreed 100% with that. However, since measuring pressure with numerous cast bullets of thye same alloy at pressure from the sublime to maximum with different burning rates of powders and discussing the subject with several ballisticians I will have to disagree with it now as I've found it just isn't so. This is why many loads are being reduced from the old CUP measurements. CUP was simply the absolute pressure. With modern piezo transducer and strain guage measurments we get the complete time/pressure curve and understand much more of what it does to bullets, especially cast bullets. The concept that "pressure is pressure" is no longer valid.

The slower you push the bullet to the same psi the less will be the deformation from inertia, especially at the base and in collapsing lube grooves. If you have an alloy that has a yield strength to take the psi of a max load of Bullseye without deformation then accellerating the bullet with a slower burning powder isn't going to make a difference.

However, you can take a softer alloy that has peaked out accuracy and psi wise with Bullseye (or any other faster burning powder) and accelerate it to a higher psi and velocity with a slower burning powder before before accuracy deteriorates from bullet deformation during accelleration.

The faster the accelleration the greater the adverse affect inertia will have. Accellerate the bullet slower to the same psi and the less adverse affect inertia will have. That applies to handguns as well as rifles. When it comes to deforming cast bullets "pressure is pressure" is not correct because the time to get to that pressure is also critical.

Larry Gibson

[geargnasher]

Arg.

Larry, you say your experiences disagree with my statement, then say exactly the same thing I said.

Look, when loading to "estimated" peak pressures using existing, generic pressure barrel data that is 10% less than the measured ultimate compressive strength of the alloy, PRESSURE IS PRESSURE, PERIOD, NO MATTER THE BURN RATE. Know why? Because your lube grooves don't collapse, and your base bands don't wad up, and the damage to which you refer just doesn't happen to the boolit if your peak pressure is within the elastic limit, but below the ultimate compressive strength, of the alloy. Make sense? I'm only saying that "pressure is pressure" when confining one's pressure to the limits set by Lee's formula, not any other situation at all!

The 10% fudge factor is built in to account for a reasonable amount of variable things like rifling skid, different characteristics of different alloy blends with the same ultimate compressive strength, etc., and it's also important to get enough pressure to get into the elastic zone of the alloy when following this loading method. Lee's straightforward loading algorithm simply works, and for some reason all the experienced cast boolit shooters want to ignore this and blow it off because of all the things they know far beyond that simple method. I don't know why, this method is extremly valuble in my opinion to a beginning cast boolit shooter, or even as a jumping-off point for a brand-new caliber/cartrige/gun for someone with a reasonable amount of experience.

All that being said, OF COURSE you are correct in all you say about rate of pressure build, deformation from static inertia (nose slump, rifling skid, boolit accordion, etc. comes to my mind when you mention this and I assume you were thinking the same thing), rate of acceleration and all the compound forces this places on concentrated areas of the boolit, and on and on, but you ran right over my point. Every time I have stuck to Lee's formula using estimated published pressures and the fairly crude but effective method of measuring alloy strength with the Lee tool, I get excellent accuracy at or within a small percentage of the figure the formula gives for powder charge with a wide range of powder burn rates. Obviously, anything can be taken to extremes, and you wouldn't use 3031 in the .45 ACP, nor would you use Clays in the 7mm Remington Magnum, and you wouldn't try to shoot pure lead out of a .30-'06, and we have to assume the boolit fits the gun reasonably well and the ammo is loaded correctly, but the fact remains for me at least that the Lee formula works, and SOME people might find that very handy, though not so much for those who have more experience and greater understanding of what the're doing.

I guess what I'm essentially trying to point out is that not everyone's goals are the same, and just because something doesn't fit into your particular puzzle (or mine either, most of the time!) it's no reason to blow it off for someone else, although I sure think it's important to mention that the Lee algorithm is very limiting and doesn't tell the whole story. Some people don't want the whole story, they just want a simple way to be able to quicky and cheaply bypass much of the mystery and arrive at a fun and economical plinking load that shoots straight in a given gun with components they likely have on hand.

Gear

[Bret4207]

Personally, I think your bullets at 23 bhn are quite hard enough if, only if, the firearm likes the particular bullet design. Gas checks do a lot by moving the force of the blast forward onto the driving bands rather than the base. This is all in elasticity of lead. It causes the middle driving bands to swell from the impact on the base rather than, causing the base to swell, dish out, or gas cut. I dislike the vague idea that they scrape the lead out of the bore, I think they do a lot toward never letting it start, in the first place.

Good Luck,
Ron

Ron, would expand on what you're trying to say here please? How is it you are thinking the pressure passes by the GC and onto the bands? And how does you theory figure for properly fitted boolits that don't need obturation within the bore? Maybe I'm just misunderstanding what you meant.

[Larry Gibson]

Gear

As usual we're saying the same thing.....just taking two different trails to get there:D

Larry Gibson

[Mossy]

I love this forum! I truly appreciate all the discussion and food for thought. It's what drew me to this site. I'm often reminded that I "over-analyze everything", but I don't consider that to always be a bad thing. Thank you all. I prolly give too much thought to my starting loads BEFORE I load the first one, but that's just my way.

I've decided to try a 50% of max load of H4895 with kapox fill as a starting point and print a few dozen at .3 grain increments.

Thanks again

-mossy

[runfiverun]

larry:
in post 20, your last two paragraphs.
thats what bass was saying in the rpm thread. [the old one not the last one]

brett:
i don't see how pressure is tranferred to something being contained either.
but as i recall elmer talked about square lube grooves being best bcause the pressure on the base of the boolit would help force the lube against the bbl walls. [shrugging here]

anyways gas checks are just that gas checks.
they will help grab the rifling and spin the boolit.

[Larry Gibson]

That is indeed what Bass was saying, it is also what I was saying then and still say when visiting cast bullets at high velocity. A slow burning powder is necessary to keep bullet deformation (i.e. becoming imbalanced) at a minimum during accelleration.

Bass and I agreed on a lot of things during those RPM discusions. Our experiments with 311291 demonstrated we both had the tecknique down for pushing the RPM threhsold upwards. Even with the 45 2.1 highly criticised 311291 from my mould both Bass and I were able to push it to 2200 - 2300 fps with 2-3 moa consistent accuracy. Bass did it in one 10" twist '06 and I did it in three 10" twist '06s. The key was using a slow burning powder that gave consistent ignition (measured by velocity SD/ES and psi SD/ESs). I've also got some very good HV accuracy out of Bass's 150 gr LBT bullets (excellent design for HV .30 cal loads). With 10, 12 and 14" twist barrels I've gotten 1.5 moa or less accuracy (10 shot groups BTW) at 2300 - 2600+ fps from '06s and .308Ws. It was/is done using that LBT cast bullet and the 311466 cast bullet with slow burning powders as you won't git 'er done with fast and medium burners.

Larry Gibson

[Dthunter]

I couldnt aggree more Larry!
Simply put.