Max Pressures and reloading...

[Schleprok62]

OK, still being something below any kind of knowledgeable about technicals... I guess this Q is directed at our resident gurus...

OK, I'm looking at two of my reloading manuals trying to decide which load to use for the 68gr hornady HPBT's... looking at max pressures and seein wide margins of difference from one load to another... I notice in some cases max load comes no where close to max pressure with one powder and that pressure is lower than the pressure of another powders "starting load."

Now, my question is: Is this more because of case capacity limitations with one powder than another> Or, is there a whole lot more to it than that?


(understanding the physical nature of ball powders vs extruded vs flake) i.e Varget is and extruded and BL-C(2) is a ball powder.


I think I said this correctly... if not, I guess I'll not hear the end of it... LOL

Thanks...

Tom

 

[rfwobbly]

I'm CERTAINLY NO EXPERT, but there are several issues that may limit the powder charge besides chamber pressure, such as....

• Powder volume. Maybe the case simply cannot hold any more powder, OR that type powder becomes unstable with "compressed loads".

• Bullet speed.
a) Some types of bullets don't like to be pushed quite as fast. This could be due to rifling twist vs bullet weight, jacket material, or bullet design.

b) Calibers do have maximum speeds. 3000 fps is achievable in a 223, but is unthinkable in a big bore gun.

• Action. There are certainly different limits for a 223 bolt action and a 223 gas operated (AR) action.


Hopefully this will suffice until a REAL expert gets here!

 

[rcmodel]

If I understand your question:

It is all related to the burn rate of the different powders.

Generally speaking, faster powders reach max pressure sooner, and give less velocity at the same pressure as slower burning powders.

The faster powder smacks the bullet a sharper jab.

The slower powder shoves it longer.

rc

 

[Schleprok62]

hmmm... I don't think I got the wording just right.. although, both of your answers helped out a bit... but let's see if I can't elaborate a little better...

Varget, 69 gr JHPBT, Max Load=26.0c gr, Vel = 2922, CUP = 40,500

BL-C(2), 69 gr JHPBT, Max Load=26.5 gr, Vel = 3018, CUP = 50,800

with a CUP difference of over 10,000 and a velocity around 100 fps difference... in theory, is this due to a limitation of the .223 Rem's case capacity?

Then the difference in the IMR-4895 starting load (38,400 cup) is very close to the max Varget load pressures...

I hope this helps break down what I'm trying to understand...

FTR: The reference is Lyman's 48th

Thanks again...

 

[rcmodel]

Well, according to my 2009 Hodgdon manual:

26.0 grains of Varget is a Compressed load, but it is not a MAX load.
It gives 3,010 FPS at 48,400 CUP.

26.5 grains of BL-C(2) is not a compressed load, but it is a MAX load.
It gives 3,029 at 50,100.

So, stick type Varget is a less dense powder then Sperical BL-C(2), and you can't get enough of it in the case to reach max pressure with that long of a bullet.

(The burn rates are very close, but one is less dense then the other, so it takes up more room)

Am I getting close yet?

rc

 

[MutinousDoug]

I used to load a lot of of 69g Sierra to magazine length for High Power in the AR15. At 2.26" COL using LC brass, I physically could not get more than 25g of Varget into the case without compressing the powder. If I was shooting a bolt gun with a longer throat, maybe I could load 26g but 26g will be about the max case cap for .223. 4895 has approximately the same density as I recall, so it would have the same limitation. There are other powders that will yield higher velocities in the same case and are successfully used in the high power game; ball or flake powders are said to be more temperature sensitive than stick (extruded) but provide greater density it the case.

 

[33rowdy]

I think I know ware you are going with this. I think you are trying to understand how two or three companies compare a load data and you see different values in of MAX PRESSURES.

I understand the basics but not the specific details.

You are gonna have a vary on difference of sources no matter what company developed the tested load data. Lyman uses a different test gun than Hornady will and the same as Hodgdon will. Hornady will also set a different bullet debth than the other 2 also. The make of primers will adjust pressures. As you also found out that Winchester brass of the same caliber of Frontier/Hornady have a different volume of brass. The barrel length of the gun will vary pressure.

Its hard to come by things like...I want a Hornady Bullet, A Hornady case, A Hornady powder, a Hornady primer, A Hornady seating debth in my Hornady 223 rifle and my max pressure will be on the mark of the book. Will never happen.

 

[Schleprok62]

Just so everyone understands... I'm not asking these questions to see how far I can push the limits of one load or another... I'm asking from an eduacational aspect to try to understand how all these things work together to do what they do.

So, according to Lymans "max load" info, it's not actually what is considered max load? Interesting.

So case capacity isn't the only limitation as far as pressure is concerned? In theory, that is... using the .223 Rem example...

RC: the "c" next to the 26.0c was to indicate compressed... not sure if you saw it...

 

[ants]

Told to me by ballistics engineers at the SHOT Show:

They first determine the constants that will be held, including environmental conditions, type of equipment (copper crusher, strain gauge, or transducer -- yes, they still employ all three), sample size n (typically 20 shots per string), bullet, primer, case type, overall length, chamber dimensions, barrel length, rate of twist, and so forth. Generally, the only variable is the powder charge. From historic data for the subject powder and the constants selected, they determine the range of the independent variable and the delta (how many grains of powder for each string).

They shoot the strings, tabulate the data for each string, and calculate mean and the sample standard deviation for each. Typically the data yield as many as 80 curves. The max load is the curve whose mean plus two standard deviations does not exceed SAAMI maximum. For those of you with a math background, you will understand the importance of "mean plus two standard deviations". In a normal distribution, plus-or-minus two standard deviations from the mean accounts for slightly over 95% of all data, thus only 2.5% of data fall higher than the mean plus two standard deviations.

So why does the table vary from year to year? Because they don't necessarily select the same variables every year, and (as we all know) components change from production run to production run, and thus from year to year. Also, as we all know from shooting across a chronograph, the sample standard deviation depends upon the specific data from that particular string, and can vary from string to string even if you try to hold as many conditions constant as possible.

This also explains why the pressures listed on a load table are usually far below the SAAMI maximum. The pressures listed on the load table are the mean pressures, not the mean plus two standard deviations.

OK, Schleprok62, that's part of the education they gave me. I posted the same information on this Forum last year, but some members shouted it down. Maybe it's hard to believe that there is real science and engineering involved. In any case, I thought you would be interested in the number of variables involved. It's impossible to point to one variable - case volume - and explain variance that way.

 

[33rowdy]

Schleproke62; I know you are trying to lern something and I did the same thing like you are doing by asking a confusing question and you get a confusing answer. My question in here in my time was; "Load data, Manuals, ect preach to us in bold text 'caution of Maximum loads"'. Well what precautions, what should I look for on Max loads? I was told to look for flat primers, tight brass in the breach, and mic for case expansion.

Quote;
Q. So, according to Lymans "max load" info, it's not actually what is considered max load? Interesting.

A. "As in Max load" or "Max CUP pressure"? look in your Lyman book. 40,500 C.U.P is the pressure for that Max load. H335 has 51,800 C.U.P. Looking through out the book in 223, 52,000 CUP is max. Looking in a Hodgdon book, They have a load of 80 Gr Siera MK, 23C Gr IMR 4895. 53,900 CUP.

Going back to your true question "So, according to Lymans "max load" info, it's not actually what is considered max load? Interesting." Look on page 137. See the "Test Components" and the "Test Specifications" To "their" research yes it is. Hodgdon, and others that develop load data have other components and Tools in their research lab. Their gonna have different numbers too.

Q. "So case capacity isn't the only limitation as far as pressure is concerned? In theory, that is... using the .223 Rem example..."

A. That is correct. A CCI and a Federal primer can change pressure in comparing with the same volume of case and powder. Length of barrel , Twist rate, How smooth the barrel is cut inside, Moly barrel and bullets can change or adjust pressures.

Again; I hope I helped you. Not confused yea.

 

[rfwobbly]

RC: The burn rates are very close...

Close enough to be cousins, but not siblings. The BLC-2 is the faster, which has to account for some of the excess pressure.

 

[33rowdy]

Thanks for teaching me something Ants. I was also one that got shouted down.

 

[Schleprok62]

OK... So, in theory, using the Lyman data, if the Varget powder was more dense, then we could safely achieve more performance from the same case capacity. ?? i.e a little more powder could be used to achieve a higher, but still safe pressure?

Yes, I am confused, but this is normal for me, as it will all come together like a cast iron skillet to the forehead as it filters itself through my braincells.

I very much appreciate all of you taking the time to share your collective knowledge...

 

[pmeisel]

They shoot the strings, tabulate the data for each string, and calculate mean and the sample standard deviation for each. Typically the data yield as many as 80 curves. The max load is the curve whose mean plus two standard deviations does not exceed SAAMI maximum. For those of you with a math background, you will understand the importance of "mean plus two standard deviations". In a normal distribution, plus-or-minus two standard deviations from the mean accounts for slightly over 95% of all data, thus only 2.5% of data fall higher than the mean plus two standard deviations.

Thanks for posting that. It would be interesting if they published the standard deviations as well.... and explains why our more aggressive experimenters load a little heavier without obvious bad effects.

 

[33rowdy]

Quote
"OK... So, in theory, using the Lyman data, if the Varget powder was more dense, then we could safely achieve more performance from the same case capacity."

For crushing the powder in the case in a compress load; I will say yes.

Quote.
"?? i.e a little more powder could be used to achieve a higher, but still safe pressure?"

I assume you are saying "Over Max Load Data?" Well I don't want to be the one to just yes for that answer. But like the Engineer above says;
"So why does the table vary from year to year? Because they don't necessarily select the same variables every year, and (as we all know) components change from production run to production run, and thus from year to year. Also, as we all know from shooting across a chronograph, the sample standard deviation depends upon the specific data from that particular string, and can vary from string to string even if you try to hold as many conditions constant as possible."

If My Old #9 Speer manual gives me a max Load data that's higher than my newest #12....I myself would try it. That is if my gun is in good condition. Not some fragile old war relic or anything of its nature.

Schleproke62; If I can ask...How did you stumble across this problem that you need to know more about "Max Pressures"?

 

[bullseye308]

It would be interesting if they published the standard deviations as well.... and explains why our more aggressive experimenters load a little heavier without obvious bad effects.

The second part answered the first. Folks know that they "can" go a little over published max at times with the proper precautions and I would expect that the publishers of the data know this. That alone could be a lawyer reason to keep the published max a few percent under what it really could be, for those few that will go over just a little that may not have the experience needed to be doing such a thing.

 

[Schleprok62]

How did you stumble across this problem that you need to know more about "Max Pressures"?

It isn't a problem of any sort... I was looking up load data for some 68gr Hornady BTHP's and looked at the max CUP's and saw such a wide diference that got my curiosity started...

Generally speaking, I have yet to load anything that close to the "max load" specifications... I am generally in the middle of the road and enjoying the hobby...

Again, I am asking this for curiosities sake, and educational purposes...

No worries friends... I'm not about to see how far I can push a load before I blow a gun and/or mysellf to smitherines...

 

[Schleprok62]

ok, I think I got the original question all snookered up for you folks... let's try it this way:

if max saami pressure for the .223 Rem is 55,000 cup... and a particular "max load" is listed as giving 40,000 cup...

There's a 15,000 cup difference here. Is this due in part, or wholey, to the limitation of case capacity?

I'm guessing that if there was more usable space for a little more powder, it should be possible to get closer to saami max pressure... yes???


Again, in theory...

 

[MCMXI]

if max saami pressure for the .223 Rem is 55,000 cup... and a particular "max load" is listed as giving 40,000 cup...

There's a 15,000 cup difference here. Is this due in part, or wholey, to the limitation of case capacity?

I'm guessing that if there was more usable space for a little more powder, it should be possible to get closer to saami max pressure... yes???

I think you're absolutely right ... powder density and case volume are the limiting factors for some powder/bullet combinations due in part to COL limitations resulting from magazine length issues. There's lots of talk of "overbore" calibers but I wonder if the .223 in the AR platform is an "underbore" caliber. In other words, 77gr and 80gr bullets could be pushed a lot faster with good results if it weren't for the limited case capacity. I don't own a .223 bolt action but from my experience with reloading/shooting .223 in ARs and Mini-14s, the most consistent loads in terms of velocity and accuracy are either compressed loads or very close to it. That's certainly the case for IMR 4895, Varget and Reloder 15.

 

[NCsmitty]

One of the ways around the 223's limitations is to increase the efficiency of the case, hence the 223 Ackley Improved. You cannot use it in AR platforms due to it's higher pressure limits at Max loadings.

The .223 Ackley Improved was developed by applying standard Ackley modifications to the .223 Remington (5.56mm NATO) cartridge case, yielding greater powder capacity, higher pressure and increased efficiency.

The parent cartridge already provides relatively high-performance in factory trim, so a significant increase in case volume was not expected. However, a substantial improvement in performance is realized by specifying nearly 20% higher operating pressure for the Improved version, approximately 65,000 psi. This limits the .223 Ackley Improved to modern bolt-actions, preventing application in conventional semi/full-automatic firearms based on the parent case.

In Cartridges of the World (9th Edition), Barnes stresses the benefits of this approach: "...Comparing this number to any of the more powerful .22s, we see that it has two distict advantages: 1). significantly increased barrel life and 2) vastly reduced barrel heating..."

COTW expounds that the highly-efficient .223 Ackley Improved "...gives up very little useful range to the various Swift-class numbers..."

It's noted that it shoots a 55gr bullet @ 3528fps.

NCsmitty

 

[redneck2]

In other words, 77gr and 80gr bullets could be pushed a lot faster with good results if it weren't for the limited case capacity

They're called "magnum" calibers. Of course you could get more velocity. I think Roy Weatherby (among many others) did this 50+ years ago.

You can get excessive pressure and still get the same or less velocity. To a great extent, bullet speed is determined by "area under the curve". A super fast powder would give a high pressure spike, but run out of steam rather quickly. Even though you get a high spike, you most likely get lower velocity. This is the reason magnums use more quantity of a slower powder. Since the powder burns more slowly, it pushes over a longer period of time without the extreme pressure spike associated with fast powders.

Slow powders tend to better fill the case and tend to be more forgiving.

 

[sqlbullet]

At the end of the day it is a max load because it was the heaviest charge of that powder which could be safely fit into the case with that bullet.

The 'why' can depend greatly. It may strictly be a volume issue. Or it may be wild deviations on any greater charge. Or it may be some other factor.

Without access to the raw test data, we can't tell. We can only guess. Guessing is bad in this hobby.

 

[33rowdy]

The question is:What do I look at, at what is a safe load? MAX CUP or MAX powder charge?

Yes I think it will be a safe load. I hear of people filling the brass and over flowing it and pressing the bullet in. "Typically" slow burning powders work best for accuracy. So they put in the slowest and all that can fit and still under CUP.

 

[41 Mag]

ok, I think I got the original question all snookered up for you folks... let's try it this way:

if max saami pressure for the .223 Rem is 55,000 cup... and a particular "max load" is listed as giving 40,000 cup...

There's a 15,000 cup difference here. Is this due in part, or wholey, to the limitation of case capacity?

I'm guessing that if there was more usable space for a little more powder, it should be possible to get closer to saami max pressure... yes???

One other thing that the manual data is trying to keep in check is the vast differences in firearms chambered for particular loads, when they work up their data.

Yes, there is some SHTF consideration built into their process, and yes, in reality you can possibly squeeze out a few more inklings of FPS over what is listed. You also have to realize that as handloaders delve into this data, we might have bullets made by JC Custom or Remington, or Hawk, all being the same weight, but far from the same profiles or jacket construction. Thin jackets have issues, thick jackets have others, and tubular jackets can induce other issues.

With all of the differences out there that can and do push pressures around they want to make it as lawyer proof as possible and still produce guides which will get you to the end product with a safe and productive product.

Similar to making up a batch of brownies, depending on your background the basic ingrediants are the same, however there are some who make mild ones and some who push the envelope and make some very high octain ones. Most prefer the middle ground ones which melt in your mouth and give the most satisfaction, with out the added side effects.