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Old 06-29-2018, 01:30 PM
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Default extrapolate loading tables?

Gentlemen, I've only been reloading for a few years and have stuck to published tables because the object was to have ammo during an ammo drought, not wildcat or push limits. This morning I was loading some .44 Special for a recent purchase and a question came to mind. I've already loaded and fired 50 rounds from the bottom of the table and wanted to move up. The question is, are the velocities listed between minimum and maximum linear. If I go to a middle load, will the velocity be about in the middle of the range, or is there a curve. When I'm rich I'll buy a chronometer. Thanks much.
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Old 06-29-2018, 01:47 PM
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They could be but not necessarily.

Different powders will burn at different rates depending upon pressures which may not be linear. There may be linear portions of the pressure / velocity curve and you may find that various powder manufacturers will tend to publish data on a flat portion of the curve. generally when you get above the top listed load is when things can get hairy with the pressure / velocity curves.

When you chronograph your loads and work up in say .2 or .3 grain increments you may reasonably expect to see equal velocity gains with each change in powder charge. There will be a point where you will see a lower velocity change with the powder charge. This is where the pressure is going to start spiking and go non-linear. AKA - time to back off and back down.

Some powders such as WW 296 or H110 warn against going lower than the listed minimum due to possible pressure excursions.

My advice would be to check several sources, different bullet manufacturer's data as well as the powder manufacturer's data to come up with a range of loads.
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Old 06-29-2018, 01:53 PM
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Thanks, elpac3. Looks like it's time for a chrono. I was loading from the hornady tables using AutoComp and went from 5.5 gr (769 fps) to 6.0gr. The table shows max as 6.5 gr for 903 fps.
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Old 06-29-2018, 02:18 PM
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I spent the money on a chronograph after my handloads failed to make power factor in a comp and I ended up shooting in the “.45 Minor” Division a few years ago. What I have discovered putting rounds over the screens every time I work up a load, or even buy another batch of powder, is that .1 or .2 of a grains difference either up or down can often not effect velocity much at all. And that all guns are different.

In my Kimber 9mm 1911 a .2 gn drop from the manufacturers maximum listed load will not result in any loss of velocity, but it does effect accuracy with the “lighter” group being over 25% larger and off centre.

And in my .45 1911 a maximum published load failed to make power factor with two different powders.

Also remember that published tables are formed with liability in mind. Rifle loads that I assembled 20 years ago from powder manufacturers tables are now considered overcharge with maximum published loads well down.
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Old 06-29-2018, 03:28 PM
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Published data is for the exact platform & components. Then throw in powder burn rates, faster powders build pressures & vel sooner than slower powders. So no, vel is not often linear.
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Old 06-29-2018, 07:21 PM
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Interpolating is moving between know starting data and max data. That is a safe know practice. Extrapolating is attempting to arrive at a safe point outside of known safe starting and maximum parameters. We are going outside safe practices when we extrapolate.
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Old 06-29-2018, 07:49 PM
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With the Hornady Reloading Manual 8th Edition, for every cartridge, it shows a starting load with a starting velocity and they increase in 50 fps intervals until the maximum load and velocity is reached.
No extrapolating required .
The 38 Special with 140 grain lead FP cowboy bullet, using Titegroup powder has loads starting at :
3.0 grs. = 700 fps , then moves up
3.3 grs. = 750fps
3.7 grs. = 800 fps
4.0 grs. = 850 fps
4.3 grs. = 900 fps
to a maximum load of 4.7 grs. = 950 fps

I find with the Hornady manuals it helps me verify those middle of the road loads I usually find best. If you don't have one of their manuals , it's a good one to get.
Gary
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Old 06-29-2018, 08:05 PM
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Same powder same bullet, I divide weight of powder charge
by velocity = fps per grain of powder. Do this with Max & Min
charge. Then average and divide by 2. This will find the middle
loads not listed by multiplying this number by powder weight.
Maybe not perfect science but I never had a problem doing this.
I have only done this with straight cases and mostly pistol cals.
You know you are operating in the safe anyway, because you
are less than max load. It is not exacting as a chrony because
of many varibles but good enough for my purposes. I really
don't care about the precise FPS as long as Im getting the
accuracy I'm after.
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Old 06-29-2018, 11:06 PM
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Quote:
Originally Posted by gwpercle View Post
With the Hornady Reloading Manual 8th Edition, for every cartridge, it shows a starting load with a starting velocity and they increase in 50 fps intervals until the maximum load and velocity is reached.
No extrapolating required .
The 38 Special with 140 grain lead FP cowboy bullet, using Titegroup powder has loads starting at :
3.0 grs. = 700 fps , then moves up
3.3 grs. = 750fps
3.7 grs. = 800 fps
4.0 grs. = 850 fps
4.3 grs. = 900 fps
to a maximum load of 4.7 grs. = 950 fps

I find with the Hornady manuals it helps me verify those middle of the road loads I usually find best. If you don't have one of their manuals , it's a good one to get.
Gary
You realize the hornady manual is NOT giving exact vel but a range. Sierra is sim, no way to interoret or extrapolate from that. The only way to know what your loads are doing is a chrono, everything else is a guess.
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Old 07-01-2018, 04:31 PM
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I look at velocity as not being very important as long as it's in
the practical range for the cartridge. I never load to achieve the
highest velocity possible. Pressure is more important but all the
manuals are geared to the industry standards. There is nothing
absolute, it all falls in a range of safety. I usually start at factory
duplication posted velocity for bullet weight and look up that
velocity for the powder I'm planning on using. I might go through
several bullets of same wieght & different powders till I get what
I want. If it's not a accurate load getting there 100 fps faster
doesn't help. On the other hand their is no point in loading down
for accuracy to the point you lose the advantage of the cartridge
you are loading for. A lot of beginners run down the specs and
pic out the highest fPS which means the lightest bullet. This may
work out in some cases but it never has for me.
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Old 07-01-2018, 09:03 PM
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First, nearly all of you need to read mtgiani's comment, post #6, since you do not know the difference between extrapolation and interpolation! These are not synonymous terms.

To answer the OP's question, yes, within a reasonable degree the velocity trace is reasonably linear. This is especially true of single-base propellants. Double-base propellants are also quite linear up to their so-called "balance point" that we generally have no way of determining. This is not true of pressure however, although the relationship can be reasonably estimated within known, documented limits.

The general rule is that velocity will increase/decrease in approximately direct proportion to the charge weight change. A 5% increase in charge weight will increase velocity approximately 5%. However pressure increases at double the charge increase! A 5% charge increase will increase pressure by approximately 10%. However, the pressure can tend to spike as the maximum limit is approached, and this can be unpredictable, particularly with double-base propellants. (Note: Original source of this information was from a document published by the DuPont ballistics department years ago!)

Contrary to what is popularly believed, the loading table data published in most re-loading manuals is, in fact, calculated based from a base velocity/pressure standard determined by firing tests. The remainder of the table is then determined be interpolation/extrapolation. Certainly you didn't believe that the bullet companies fired thousands of rounds to determine exact loads for specific velocity steps as published in their respective manuals did you? The calculations are really quite simple, and perfectly safe to use as long as you have a known starting point for P/V, and do not attempt to extrapolate to great a range! For example, calculating .44 Magnum data based on .44 Special data would be both foolish and dangerous. While calculating .44 Special data from base .44 Magnum data is perfectly safe, but you would be getting in the area where pressure could be too low.
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Old 07-01-2018, 10:16 PM
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Quote:
78bagger asked:
The question is, are the velocities listed between minimum and maximum linear.
For the reasons elpac3 noted in the second paragraph of Post #2, no.

As elpac3 noted in the third paragraph of Post #2, proper load development is to begin with the starting load and increase the charge incrementally until you see signs that you are near (or have exceeded) maximum. One of these signs may be where you increase the charge by 0.2 or 0.3 grains and see little if any change in velocity.

As you work your way up from the starting load, but before you start to approach maximum, you may find the changes are close to linear, but they cannot be trusted to stay that way across the entire load and there is no sure way to predict when the "curve" will start having dramatic changes.
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Old 07-02-2018, 12:57 AM
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Quote:
Originally Posted by 78bagger View Post
If I go to a middle load, will the velocity be about in the middle of the range, or is there a curve.
Yes, it will be about in the middle. Close enough that it's not going to make a material difference considering all the other variables that can affect your handgun's performance.

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Old 07-02-2018, 09:32 AM
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Too many veryables.

You will stand a better chance of the velocities being linear with fast burning powders like AA#2/bullseye/clays/titegroup/reddot/HP-38/ETC.

Myself, I wouldn't worry about velocities and concentrate more on getting a good seal of the cases. 44spl data flat out sucks, the mfg's don't know if the end user is going to be using a modern firearm or Auntie- M's 1913 top break revolver. You want to start with the starting load and look at your cases. You don't want to see them have smug marks on 1 side of them from too little pressure/powder. Once you get a good seal with your powder/bullet combo, then work the load up. Some 44spl testing done this way, 1st get a seal & then work the load up. 25yd 6-shot groups with 175gr & 162gr wc's/44spl


The 44spl is an extremely accurate cartridge if you take the time to read your brass. While accuracy has nothing to do with velocity/linear climb. It is something the reloader can also test for while increasing the loads. You'll watch you groups tighten up/walk in as you increase your load and open up/walk out as you keep increasing the load.

If you'r using standard bbl lengths and loads that are not too light for the 44spl. You shouldn't have extreme spreads to begin with. An extreme spread for the 44spl is +/- 150fps with "standard" pressure loads. The 38spl in comparison can be +/- 300fps with "standard" pressure loads.

You will find with the 44spl that once you find a bullet/load combo that seals the chamber/cylinders. You'll be lucky to have more than 75fps difference in your load development as you climb from a load that seals to a max load.

The 44spl has been 1 of my favorite cartridges, I've owned firearms chambered in 44spl since the 80's. I've shot countless 1000's of 44spl's using multiple powders/bullets. 44spl's and wc's/hbwc's are made for each other.


Glad to see you're enjoying the 44spl.
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Old 07-02-2018, 09:45 AM
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No, not linear, but who cares? The points you would be interpolating between aren't very accurate, anyway, for all of the reasons stated above. Go ahead and interpolate, and don't obsess on the accuracy of your conclusions.

Never extrapolate, even downward.
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Old 07-02-2018, 10:31 AM
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Default Very little is linear.....

If you are out on a limb, work up the load very carefully. I started an experiment, but lack of data stopped me. I'm sure I can go higher than my last load, but I don't know HOW how. I think I may crawl up in the charge in a heavy duty gun instead of the compact that I want to use the load in.

Also, I don't see where extrapolating down is a problem unless you stick a bullet in the barrel.
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Old 07-02-2018, 11:34 AM
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Also, I don't see where extrapolating down is a problem unless you stick a bullet in the barrel.
Well, sticking a bullet in the barrel usually isn't disastrous, at least at the range, but at least a couple of powders, H110 and 296, can have strange problems when underloaded. The manufacturers warn about this, and so did elpac3, above.

You know, in this country, pretty much anyone can reload ammo. No license, no exam, no training, no education. It would behoove the responsible reloader NOT to innovate or to take ONE STEP outside established guidelines before receiving a fairly thorough education in the subject of reloading. Earl Naramore's book, once sold by the NRA, might be a start. I have studied it, and I realize that I will NEVER be more than a by-the-book reloader. I also know that one must choose "the book" carefully. Speer's #8, for example, was fairly widely known for having a few irresponsible loads, hardly surprising considering that they didn't pressure test their loads. Art Alphin's book, on the other hand, gives some excellent safety advice, including the advice that you should use a chronograph to ensure that you are not beating factory loads, because if you are beating factory loads, you are probably screwing up.

"Don't extrapolate" is loose but possibly acceptable advice. A little more conservative advice might be "If you don't know why not to extrapolate, you're not yet ready to reload."
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Old 07-02-2018, 03:25 PM
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Extrapolation is necessary when you have a wildcat [cartridge A] with a similar bore and case capacity to another [cartridge B]. If I have a 6.5 bore case with a 46 gr water capacity, I can compare it to a .257" bore and a case with 44 gr water capacity and a 7mm bore, 44 gr water capacity to see what start loads run between bullets of similar weight and length. I know that my wildcat [cartridge A] will never be listed in a loading manual, but can extrapolate starting loads from the other two to arrive at a start point. I cannot safely extrapolate maximum loads but a chronograph will let me know as I approach targeted velocity.
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Old 07-03-2018, 05:47 AM
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Quote:
Originally Posted by mtgianni View Post
Extrapolation is necessary when you have a wildcat [cartridge A] with a similar bore and case capacity to another [cartridge B]. If I have a 6.5 bore case with a 46 gr water capacity, I can compare it to a .257" bore and a case with 44 gr water capacity and a 7mm bore, 44 gr water capacity to see what start loads run between bullets of similar weight and length. I know that my wildcat [cartridge A] will never be listed in a loading manual, but can extrapolate starting loads from the other two to arrive at a start point. I cannot safely extrapolate maximum loads but a chronograph will let me know as I approach targeted velocity.
Interpolation.
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Old 07-03-2018, 06:29 AM
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Let me suggest you google John Taffins Book of the .44. Then, go to chapter 43
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Old 07-03-2018, 10:18 AM
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Quote:
Originally Posted by BLUEDOT37 View Post
Yes, it will be about in the middle. Close enough that it's not going to make a material difference considering all the other variables that can affect your handgun's performance.

.
About is correct but that assumes quite a bit. Since the book vel can be waaay diff than your gun.
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Old 07-03-2018, 10:20 AM
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Quote:
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Extrapolation is necessary when you have a wildcat [cartridge A] with a similar bore and case capacity to another [cartridge B]. If I have a 6.5 bore case with a 46 gr water capacity, I can compare it to a .257" bore and a case with 44 gr water capacity and a 7mm bore, 44 gr water capacity to see what start loads run between bullets of similar weight and length. I know that my wildcat [cartridge A] will never be listed in a loading manual, but can extrapolate starting loads from the other two to arrive at a start point. I cannot safely extrapolate maximum loads but a chronograph will let me know as I approach targeted velocity.
Extrapoation is also useful when loading bullets in common calibers that are not common for that cartridge. 160-165 gr 9mm is a good example.
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