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powdr, my "opinion" is just reciting some mathematical relationships others have put forth. I never said you couldn't use the same powder to good effect!

Frankly, there is no such thing as a "3% slower powder." Such a statement means only that the optimum powder for the larger case has to be somewhat slower in gas generation ("burn rate") if you plan to fully fill the case. Filling the case is usually the route to maximum velocity, for it maximizes the chemical energy available to each grain of bullet mass. Whether you fully utilize that potential chemical energy depends on the burning characteristics of the powder, and burning characteristics simply cannot be reduced to a single number.

Keep in mind that 3% is a small change, less than the difference between 4831 and 4350. One might well be running the parent case nicely with a powder that's a wee bit slow for it; using it again in the blown out case might leave you with a powder a smidge too fast. Neither would be optimum, but neither would be bad. Further, it's quite possible there is no other powder that would do better in either case. Trying to distinguish such a fine difference without good quality pressure measurement tools is nearly impossible.

As for your observation, how exactly have you proven to yourself that you have the optimum powder for your blown out cases, or for the parent case, or that you've been operating each at the same peak pressure? As you point out, there is a mind numbing number of powders to try out. When it comes to optimum loads, "knowledge" is very difficult to establish.

Regardless, to get to tcp's specific question, you can bump the charge roughly 6%--but there's no guarantee. The various ways to estimate this are not in agreement. There is no "rule" for this.

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2525, thank you so much for your response. I have on occasion in my younger years exhausted about every powder suitable for some of the Ackley's I've had built. Using chronograph and recoil as a means to let me know when enough has been reached or when to back off. I've always wondered if the load/s I've settled on is the best for velocity and pressure...I do not claim to have a crystal ball. For instance, for years I loaded RL19 in my 257Ackley and had good results. I recently though ran out in the powder shortage and thought I'd try something else since I have almost 30 cans of powder on my bench. I decided to try IMR 4831 on the advice of several of the fire members. It is a wonderful load and just as good if not better than the old RL19 load. The fact that the powders are not far apart on the burn chart also makes me feel OK with the change. Mr. Ackley felt like his cartridges could benefit from a 4-7% increase. I've always tried to stay around 3.5-4% to be on the safe side and have never gotten into any real trouble. I got lost in all of your math and percentages but after reading it about 10 times it made more sense each time I read it. It gave some validity to what I've been doing all of these years but left some questions in my mind as well. I'll be starting with Norma 201 in my new 338-08Ackley Improved and then maybe go to TAC or IMR 8208 or maybe even try AA 2495. I really don't know but I'll get it figured out. There's not any starting data that I can find anywhere but what there is for the 338Federal. Do you have any recommendations on powders that may work? I'd gladly appreciate any advice you may give me. I'll be the first to admit I don't have all the answers but will try and get this one going like my others. I want to thank you for your diatribe, it has caused me to do some rethinking on the subject. The real problem still is though... where does a man start...especially with a wildcat as unknown as mine. powdr

Last edited by powdr; 04/23/15.
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powdr, I'm sorry I have no (good) advice to give you. There is no way to calculate the optimum powder, and none of the cartridges which I load are similar to your .338-08. Were I in your shoes, I'd do pretty much as you propose. From .338 Federal load book data, pick the powder which looks best and work from that--and consider also trying a bit heavier charge of the next "slowest" powder shown in the .338 Federal data. For such a small difference in case capacity, I can't see being more complicated than that. Barsness' 4:1 rule is as good as any; use it and your chronograph.

You pointed out Ackley reckoned his blown out cases required 4 to 7 % more powder. My hunch is the upper end would be for single base stick powders, and the lower end for double base ball powders. Hodgdon has a large amount of data showing pressure for both maximum and starting loads. The trend I see is that the double base powders have a faster pressure rise with increasing charge. Like all else in internal ballistics, that's not a solid "rule;" I'm certain I can find exceptions with a few minutes of looking.

You also mentioned the numbers I tossed out "gave some validity to what I've been doing all of these years". The fact you have your fingers and your eyesight after years of wildcatting is more meaningful than my numbers --or maybe it's a testament to the quality of your guns. The numbers I gave are only coarse approximations.

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Thank you 2525. I did not sleep very well thinking of the response I might receive. I will proceed w/great caution and intensity. On picking a powder for the 338 Federal as a starting point, in your opinion, which is better? A full case or the one that achieves the most velocity? Please don't say both. Yes, I have found that both seem to go hand in hand sometimes but have also found that for peak velocity many times a powder that does not fill the case such as BL-C2 will give the best velocity. It does seem like black magic sometimes and hand loading has been the most satisfying and mystifying thing I've ever done in my life. I haven't shot an animal w/a factory cartridge since about 1979. If you think of anything that might help me in my quest...please let me know. Thanks again, powdr

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"... thinking of the response...": to borrow a line from Monty Python, pull the other one!

Yes, a dense packing, high energy double base ball can best a full case of single base stick, and I doubt there'd be enough air space left to make ignition inconsistent. But to compare apples to apples, there's likely a slightly "slower" ball which could fill the case and deliver a bit more speed. Or maybe there isn't: It depends on how progressive is the burn. Under test, BL-C2 can do wonders in some cases, eg. the .25-35 WCF (but now surpassed in it by CFE-223); and then there's Li'l Gun in the Hornet.

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Thanks 25. I will keep you informed on my progress and what I find out. I hate like the dickens to buy any new powder since I have so much unused on my bench. I think I'll exhaust my bench supply before running out and buying new. Thanks again for your insight. powdr

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Originally Posted by ringworm
What cartridges do you gain 10% by AI?

257ai is most improved, no?


No. The 25-303AI is the most improved. Ask me how I know.

[Linked Image]

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How about a picture of the Improved version? powdr

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I think I'll just use John's method on page 1 of the thread to load my new gun. powdr

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Originally Posted by 2525
"... thinking of the response...": to borrow a line from Monty Python, pull the other one!

Yes, a dense packing, high energy double base ball can best a full case of single base stick, and I doubt there'd be enough air space left to make ignition inconsistent. But to compare apples to apples, there's likely a slightly "slower" ball which could fill the case and deliver a bit more speed. Or maybe there isn't: It depends on how progressive is the burn. Under test, BL-C2 can do wonders in some cases, eg. the .25-35 WCF (but now surpassed in it by CFE-223); and then there's Li'l Gun in the Hornet.



2525,

I'm kind of interested in this part. I understand that the "burn rates" of these medium powders are close, (3031, CFE223, and BL-C2) but I also wonder about the expected pressures.

25-35 in a Mod 94, SAAMI 44,000 psi?

30-30 is 42,000 psi, I have read

223 is 55,000 psi?

I wonder if 25% more pressure changes the burning rate?

Do you find this to be an issue in the 25-35?

thanks,

Sycamore


Originally Posted by jorgeI
...Actually Sycamore, you are sort of right....
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Sycamore, "burning rate" is ambiguous. The instantaneous rate at which gases are being produced (the "rate of burn") is a function of deterrents, kernel geometry, and the current pressure. So, yes, pressure is a big factor in that sense. However, "burning rate" is more generally looked at as a relative measurement: Can you put more of this powder or that powder in the case and not exceed the pressure limit?

In this sense, deterrents and geometry are quite important. You want their combined effect to allow the afterburner to kick in, so to speak, once the bullet gets going. Once the bullet is moving along, it's leaving behind an ever increasing volume which must be filled with gases if one is to maintain maximum acceleration. The combination of case size, bullet inertia, and bullet engraving and friction all effect how fast gas production must be at any bullet position, and whether a particular powder will be optimum in its gas generation is not simple to predict. All of these factors combined affect the apparent "burning rate," and for this reason one can not construct a reliable rate table--the problem is far more complicated than a simple ordered list.

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25 you're way too smart for me to be talking to. Geesh, this stuff is way over my head. powdr

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powdr, don't assume too much, and don't sell yourself short.

I'm no expert on this stuff. I've read a few old books on the subject, some dating to WW-II. Looking at the various plots QuickLOAD offers helps visualize some of what's in those old books.

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Originally Posted by Sycamore
I wonder if 25% more pressure changes the burning rate?

Do you find this to be an issue in the 25-35?

Sycamore, I might have an example to answer your question, but it's only one example and it might not be representative.

The .25-35-117 and the .308 Win with 168 gn spitzers are ballistic analogs. Each has the same bullet SD, and the two are quite close in bore capacity. The latter is the ratio of net case capacity to bore cross section, and it can be expressed as inches of the barrel's bore; it is to case capacity as SD is to bullet mass. If two cartridges have the same SD and bore capacity, they will, at the same pressure, ideally use the same powders, with the charges proportional.

In Hodgdon's data, ball powders are clearly the winner for the .25-35. The single base stick powders manage about 2200 fps (or a bit over), but BL-C2 gets over 2300 and CFE-223 gets a stunning 2400. Raise the pressure to .308 levels, and the sticks make a come-back, roughly equaling BL-C2, and percentage-wise they close the gap with CFE-223. At starting load pressures, the .308 data starts to look more like the order of the .25-35.

I can't emphasize enough this is only one example. Hodgdon's .308 data appears to have been shot in different barrels over the years and was likely shot by different technicians. The bullets are of different construction, and different primers were used. For such a comparison as I've made, one needs to look at the averages over a wide range of such data. I do think, though, the data would show a "burning rate" chart of slightly different order for these two pressure levels. For that matter, if you change the cartridge proportions (SD and bore capacity), you'd get another slightly different chart.

tcp, I couldn't think of two cartridges in Hodgdon's data that could be used to compare a change on the order of an AI job. Well, there's the .300 H&H and .300 Wea, but that data looks strange. Instead, I compared the .308 and the .30-06 using the same bullet, and looked at the single base stick powders. Here, the net case is about 29% more (well beyond the nominal 10% you mentioned), and I found the charge could increase about 14%. So, for each 10% of case, you get a bit less than 5% more charge. This is well below the 7.5% in the Lee "rules" and below the 6% suggested by my old copy of QuickLOAD. For two ball powders, I got more like 18% or about 6% per 10% of case increase --exactly the opposite of what I'd guessed, namely that single base stick powders would be closer to Lee's "rules" than the ball powders. Theory doesn't always match the real world! So, to answer your original question, each 10% of case will allow you about 5% more of the same powder, more or less. If you have some time and several good load books, you might compare the .300 H&H to the .300 Wea, as presented in one load book; none of my books have both in it.

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2525- Thank you for your response and interest in my question . Prior to posting it, I did try to compare ratios of cartridges as you suggested - .308 vs.30'06, 30'06 vs. 300 H&H. I choose those examples because there was abundant data available and they could be compared using the same powders I plan to use in the 6mm AI round that I am loading for.

What I found was there was too much variability between maximum book loads, paricularly in the 30'06, for me to have any confidence. The difference in Sierra's max loads with a 30'06 and Hogdon's online data is is 2-4 grains of H4350 and this in turn would skew the ratio several percentage points.

AND in loading for my own 30'06's, rarely can I get to Hogdon's max without noticing the bolt lift is a little stiff, so their max does not appear to be watered down in my experience.

I appreciate all of the input thus far and, should anyone have good data for the 6mm Rem AI using H4831 and H4350 and the Nosler 95gr BT, I would appreciate it.

Thank you.

Last edited by tcp; 04/27/15.

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Originally Posted by tcp
... there was too much variability between maximum book loads...

Yes, this is always true. The test equipment, plus differences in primers, bullet construction, powder lots, etc. all have an effect. In the Hodgdon data, one could at least get the same bullet in a few of the .308 / .30-06 comparisons. Being unable to control all the variables makes it difficult to extrapolate or interpolate from load book data.

For what it's worth, I seldom go much beyond the starting loads in the books, and I keep my measured speeds to those levels.

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