Load data compromises

[gregjc9]

I just picked up a Lyman 49th and a Speers #14 reloading manuals today. I'm obviously new to reloading, and I'm trying to learn and understand the load variances between the different manuals. So far, my head is about to bust.

I have three questions:
COL for .45 - I plan on loading .45 with 200 gr TMJ RN bullets from RMR. The Speers manual lists a COL for a 230gr TMJ RN to be 1.260". The Lyman lists a COL for the same bullet as 1.275" Given the standard COL is 1.275", can I use this COL for my 200 gr bullets, but use the start charges listed for 200gr?

COL for 9mm - The Lyman's manual specifies a COL of 1.115" for 147gr TMJ (assuming RN based on pic), the Speer specifies a COL of 1.135" for TNJ RN. Which COL would be best to start with? I assume the COL that is closest to the standard COL would be, to prevent increased pressure.

Different Start Charges - There seems to be a big difference between what the Lyman's manual recommends, and what Speers recommends. For the same 200gr .45, Lyman's s/c for Bullseye (using this powder as an example) is 3.4gr, where Speers recommendation is 5.2gr. Speers seems to be higher on their s/c across the board. Which do I go with?

Sorry for the probably dumb questions, but trying to make sure I do things right. I tried searching, but couldnt find what I was looking for. TIA

[Unclenick]

No dumb questions. Safety first.

1.275" is not a standard COL, it is the maximum COL you can use and still guarantee to fit inside standard magazines. That's all that number is for. Loading shorter is done all the time, as some bullet shapes require it. Same for 1.169" in the 9 mm. It's a magazine fit limit.

That said, the deeper you seat a bullet, the higher the pressure, so you don't want to get carried away with that. A difference of 0.015" in the .45, however, is not significant. The shorter number for that bullet is probably recommended just to avoid normal seating tolerance exceeding the maximum on the occasional round. Others ignore that concern because most guns have some magazine wiggle room for a little bit of extra length.

Speer loads have been famous for being too hot in the past. They have backed down a number of them from past volumes of the manual. Some of the early Hornady data was the same way, but not now.

Here's the basic problem: The tighter a chamber is, the higher the peak pressure you get. Manuals that give pressure numbers, whether it is in psi or the obsolete copper crusher units (cup), either way you know the load was developed in a test barrel. When SAAMI specifies a round you get three drawings: The cartridge, the chamber, and the test barrel. The cartridge dimensions are given as maximums with a minus tolerance. The chamber dimensions are given as minimums with a plus tolerance. SAAMI wants all compliant cartridges to fit all compliant chambers, and that approach keeps people from making top-of-the-head calculations that conflict with fit.

The test barrel length, rate of twist, and bore dimensions are all specified tighter than industry standards. The test barrel's chamber is specified the same way as the standard chamber except the plus tolerances are much tighter, so the test barrel winds up with a minimum size chamber. That way it creates the highest possible pressures from a given load fired normally.

Many manuals don't specify pressure for their loads because they did not use test barrels. They used actual production firearms. Production firearms have chambers that are typically in the middle of the tolerance range, sometimes with added freebore. Randomly, some of those chambers are more generous than others. If the gun they developed the load in happened to have a generous chamber, the same load may produce significantly lower pressure than will be produced in your gun, even if it is the same model. This is why there is a load range. The minimum load developed this way is an estimate that should be within maximum for all guns. The maximum given is only known for sure to be safe in their particular gun. That's why you don't use manual maximums for your first load. You start at the bottom and work up.

Manuals that do give pressures may be treated a little differently. Where pressures are shown you know the load was developed in the worst-case minimum chamber. The maximum given in those manuals is far more likely to be a safe maximum in all guns. Many folks referencing data from such manuals will start in the middle of the load range, then move up or down looking for better accuracy or other performance particulars.

But here there is still a caution to be observed. Even test barrel pressure will vary depending on how much space the brass and bullet take up within the chamber, and depending upon which primer is used? The more space the brass and bullet take up, the higher the pressure. This means, for the pressure data to be correct you have to use the same capacity case (usually by using the same brand) and primer brand and number. The amount of space the bullet takes up depends on how deeply it is seated? So you also have to match the COL used for any particular bullet. This is much more of an issue in short handgun cases than in bottleneck rifle cases because a little bit of seating depth change has a much bigger percent effect on available powder space in the short handgun case with a full-diameter bullet.

Hodgdon's data is the most widely used data that is pressure tested. It uses Winchester cases. The primers vary. If you haven't done so already, go to their site and list the load you are interested in. Then click on the "Print" button. The data that comes up for printing has a header that gives the case, primer, and barrel length used to develop the data. I click on it even when I'm going to cancel the printing, just so I can see that. It seems to be good data.

In the .45 ACP, with 230 grain round nose jacketed bullets, the classic old military load is 5 grains of Bullseye. That is safe in any case brand, AFAIK. The ballistic result is equal to modern commercial grade hardball, producing about 350 ft-lbs from a 5" barrel. I measured a bunch of hardball of different commercial and military headstamps, and found COL's from about 1.250" to 1.270". The military stuff tended to be in the range of 1.265" to 1.270", for the most part. I know my guns will handle slightly long rounds in that bullet shape, but I never know when I might obtain another gun, so I usually go for 1.270" for my stock hardball and don't worry any more about it. 5.4 grains of Bullseye will get you military hardball numbers, which are just under 400 ft-lbs from a 5" barrel. I don't like to exceed that number, even though my guns will handle it. It is nowhere near +P, and anything I own will and has at one time or another, shot +P loads, except my wad gun. I just don't see a purpose to creating a steady diet of them.

If you have a different bullet shape than round nose, even though the weight matches, you have to watch how much space the seated bullet takes away from the powder? This is determined by how much room there is between the base of the bullet and the bottom of the inside of the case. How far the bullet base goes in is called seating depth. COL for a given seating depth changes with bullet shape. A pointy bullet will have a longer COL for a given seating depth than a blunt shape of the same weight does. That is because the pointy bullet is longer.

To get a matching seating depth, you need to know the lengths of your bullets. Next, look in your manual for the SAAMI maximum case length number. I use that rather than a measured case length because I don't want to have to add or subtract for different trim lengths. With the above information:

Seating Depth = Case Length + Bullet Length - COL

Conversely,

COL = Case Length + Bullet Length - Seating Depth


You need to match seating depth and bullet weight for the same load to develop the same pressure. For example, suppose you have a .45 ACP load for a 230 grain FMJ round nose bullet 0.640" long. You use it with a COL of 1.270". You know the SAAMI max case length is 0.898" from your manual. So, the seating depth is:

0.898" + 0.640" - 1.270" = 0.268" (Seating Depth)

Now you want to substitute a 230 grain FMJ truncated cone bullet that is 0.625" long. What should your new COL be when the seating depth matches? Put the seating depth you just found into the second formula, substituting the new bullet length:

0.898" + 0.625" - 0.268" = 1.255" (New COL)

A clever fellow will realize the difference in the two COL's is simply equal to the difference in bullet lengths, but I included the formulas so the reasoning is clear.

All the above applies in principle to the 9 mm. Use the Hodgdon data over the Speer for safety. Where your bullet isn't identical, adjust COL to match weight and seating depth. Note one caveat. The above approach does not always work out in rifles because it sometimes puts the bullet close to the rifling lands, which raises pressure. In pistol it can do that, too, but unless you are in +P pressure territory, you have headroom to handle it.

Nick

[gregjc9]

Nick, thanks SO much for taking the time for the fantastic reply. This makes perfect sense. I dont think the manuals had that information, if they did, I obviously missed it. This is definately getting printed out and inserted into my binder. I will also add the calculations into my load spreadsheet.

Once again, thank you!!!!!

[Bud Helms]

Excellent post, Unclenick.

[mongoose33]

Excellent, Unclenick!

Let me add one thing to this excellent discussion of bullet length, COL, and so on:


Gregjc9, the name of the game in reloading is working up loads. You don't simply go to the max load; you never know, in your gun, with your brass, and your bullets, how that will perform.

So you start low and work up, looking for signs of too much pressure, combined with evaluating how well the rounds do w/r/t accuracy.

I'm currently working up loads for the Hornady 9mm 124gr XTP bullet. The information on the loads I've found suggest a start load of 4.0 grains with a max of 4.5 grains (W231 is what I'm using).

So I loaded up 5 rounds with 4 grains of 231 at the OAL listed--1.100. I've also done 4.2, 4.4, and 4.5 grains.

That's likely a light load, but that's ok--I want to ensure I'm not having any difficulties.

I shoot my workup loads through a chronograph because I believe it's the only reliable way to determine what I've got. Some look at the fired cases to see if there are pressure problems, but that's not a certain clue.

So I'll shoot them through the chrono, low loads first, recording what I get, evaluating accuracy, felt recoil, and velocity to see what I've got. And if I end up close to what I consider a max velocity, I'll stop before going with any hotter rounds.

Never--ever--start at the max. Bullets, as Unclenick noted, vary, and furthermore, they vary from FMJ to lead to plated to...whatever. Different bullets, even of the same weight, have different friction characteristics in the barrel. Lead bullets, for instance, have less friction than FMJ and thus require less powder to overcome that friction compared to that needed for FMJ. Further, bullets can even have different bearing surfaces contributing to that friction (the bearing surface is what contacts the lands/grooves).

So work up the loads. Much better than having to replace your gun, fingers, eyes, or even your life.

You've already done a good thing in having multiple manuals. Being careful is paramount.

[DaveBeal]

Thank you, Unclenick. I always appreciate your knowledgable replies.

Here's the basic problem: The tighter a chamber is, the higher the peak pressure you get.

I understand this statement, but I'm skeptical about how important this is. According to the SAAMI spec I found at their website, the tolerance in the .45ACP chamber diameter is about 0.8% (0.004 in). This means that the volume of the chamber can vary by about 1.6%. All other factors being equal, this would cause the maximum pressure to also vary by about 1.6%. Is this really worth worrying about? I would think that chamber dimension variance would be "down in the noise" compared to other factors like bullet seating depth.

And while we're on this topic, since bullet lengths vary, wouldn't it make a whole lot more sense for load data to specify bullet seating depth rather than cartridge overall length?

[gregjc9]

More great info, thanks guys!!

Mongoose, yes, I'm very well aware of starting at the starting load and working my way up in small increments. I was just a little alarmed at the wide variance between the two manuals, I was expecting a little more consistency, but that apparently isnt the case.

I had previously looked at Hodgson's load data, but for some reason, almost none of the powders (nor bullet types) they list are in Lyman's or Speer's manuals (at least for 9mm and .45). So not real sure how helpful Hodgson's data will be, but I will x-reference it anyway.

All I have been researching in past months working up to this point, is starting to gel now, thanks to all.

[mongoose33]

And while we're on this topic, since bullet lengths vary, wouldn't it make a whole lot more sense for load data to specify bullet seating depth rather than cartridge overall length?

If they did use seating depth rather than OAL, how would the reloader go about measuring it?

I speculate that OAL is used with a specific bullet model precisely because there's only one thing you can really measure, and that OAL. (And yes, length can be measured from the ogive, but the point remains).

[Unclenick]

Mongoose33,

My copy of the old Hornady Handbook second edition did use seating depth instead of COL. For how to measure it, go back up to my first post and use the formulas I provided. They're simple.

Originally Posted by Dave Beal

. . . the tolerance in the .45ACP chamber diameter is about 0.8% (0.004 in). This means that the volume of the chamber can vary by about 1.6%. All other factors being equal, this would cause the maximum pressure to also vary by about 1.6%.

Dave,

I sure wish it was that easy, but, alas, no such luck.

First, look more closely at the SAAMI drawing and you'll see 0.004" is the "unless otherwise noted" tolerance for diameters. Lengths are 0.012" tolerance unless otherwise noted. One of those "otherwise noted" tolerances is the chamber length from breech to case mouth location, which is 0.898" minimum and 0.920" maximum, or 0.022" difference from min to max. It amounts to about a grain of water capacity difference or about 4.2% in chamber volume. Unlike a maximum pressure load in the 9 mm, .45 ACP pressures don't get high enough to stick the brass to the case wall, so we don't really see the full difference in chamber volume added to the powder volume, but that length is another matter.

When the primer ignites, in addition to forward firing pin thrust on the cartridge, the primer's pressure pops it out like a little piston, pushing the rest of the cartridge forward until its pressure vents out of the flashhole. As burning powder pressurizes the case, the case is pushed back like a bigger piston, reseating the primer and expanding the volume the powder is burning in. Remember that the powder volume is shorter than the chamber, with the bullet base and case head eating up a lot of it. About 15 grains water volume of actual room for the powder results. If a chamber is .022" longer in one gun than another, that whole difference is added to the shorter powder space when the case backs up. For the 230 grain FMJ at 1.270" COL, adding 0.022" to the powder space, even without swelling the brass radially, makes about a 6% expansion in powder space.

.45 ACP brass, from one brand to the next, can differ by a couple of grains of water capacity. The manuals don't all use the same brand in load development, and, frankly, most of we .45 shooters are "thrifty" and will carry home just about anything we find on the ground that looks like it will fit and doesn't have too many years of oxide patina built up on it. The range of volume in different brass seems to run from about 25 grains water capacity to about 27 grains, brand new and same length. The bullet occupies the same space, regardless of case capacity, so that difference is in head design and is all added to the powder volume, making over 13% powder capacity extreme spread. Add that to the 6% from the chamber variance, and you have almost 20% possible powder volume difference when using mixed brass.

Additionally, the matter is complicated by some chambers being supported and some unsupported. The chamber end of most barrels are not dead tight against the breech. Even a gun that's been "fit up" will have another couple thousandths there, while stock guns can vary rather a good deal more than that. There is also some tolerance in the lockup of the slide and frame that can keep the barrel a bit forward of the breech. leaving a gap for the case to fill as it blows back. Some barrels, in particular those a custom smith has handled, can be throated, which reduces start pressure.

Another factor is that pressure doesn't change linearly with powder volume. The bullet starts to move and the case is backing up before the pressure peaks, increasing the powder space by what is called expansion. The smaller the starting volume (this gets back to seating depth) the faster the peak is reached, putting all the gas into a smaller, less expanded total volume than would be if the powder got burning more slowly. The result is that pressure, for small changes in volume, goes up or down more than just by the change in volume. For Bullseye it's around 20% more than the change in available powder burning space for the .45 ACP load under discussion. So, an 8% change in volume gives about a 10% change in pressure.

Add up the slop from the gun mechanism, the worst case chamber, the different brands of cases and whatnot, it isn't hard to get 20% difference in powder space from one gun and case combination to the next, resulting in about 25% difference in pressure. I know there's a lot of supposing and worst case exampling going on there, but the bottom line is that two guns could see significant pressure differences firing the same powder charge and bullet. Not all the manuals use the same case brand, which is why I kept including that variable. Perhaps a bigger one we haven't even brought up is just that some guns are stronger than others and will work with higher pressure loads than some others will. When you consider all that, it seem fairly reasonable to expect that manual data based on a single example production firearm could deviate from safe loading practice for some other production firearm pretty easily.

[DaveBeal]

If they did use seating depth rather than OAL, how would the reloader go about measuring it?

Overall length minus bullet length.

Unclenick, thanks again for the thorough reply. It all makes sense. If you don't mind me asking, how did you come by all your technical expertise? Do you work in the firearms/ammunition industry?

[SQUAREKNOT]

UncleNick,
I was wondering if there is a tie between velocity and pressure?
I loaded 3 identical sets of loads except for the primers. I did this for both 230gr RNL and 200gr SWC in .45ACP
The WLP showed the most pressure and the lowest velocity's
The CCI was next-still has a radius on the primer
The Remingtons showed almost no pressure signs and had the highest velocity's
I was using 5.3gr HP-38 both were 1.265" OAL

[SL1]

All this discussion of case and chamber volumes has left out what I think is the MOST important variable - - power lot #.

The loads in different manuals are worked up with different lots of the powders that they list. The burning characteristics of different lots of the same powder can be different by a substantial amount, causing different pressures and velocities in the SAME gun. (That is why we are told to work-up our loads again when we change lot #s of a powder.)

So, given that different manuals used different lot numbers of the "same" powder, it is not unexpected that they get somewhat different max load values. And, since you will be using a different lot than any of that data, you need to start about 10% below the listed max to make sure that you start in a safe region.

Often, when the loads in two manuals differ by MORE than 10%, there are other factors at work in addition to powder lot variation, including the seating depths, etc. I really wish the manuals would list two parameters in their data: powder space for the load as-shot, and seating depth for a STANDARD case length. That would really help us figure out how their loads compare to ours. When they only list case manufacturer, they don't tell us the cae capacity very accurately. And when they only list COL, we need to go find THEIR bullets to see how long it is in order to load OUR bullets to the same seating depth.

SL1

[SL1]

You can't determne pressure differences caused by different primers by looking at the primers after they are fired. Different brands of primers have different cup harnesses, and would look different after firing EVEN IF THEY WERE PRODUCING EXACTLY THE SAME PRESSURE. So, that difference in hardness can easily mask actual differences in pressure, making the primer with higher pressure appear to have lower pressure and vise versa.

The only real way to know the pressure effects of changing primers is to fire them in a pressure-test barrel. (Using the pressure-ring expansion measurement on fired case might get you some information if the pressure differences are big enough and you design the measurement program carefully enough to account for all of the complicating factors.)

SL1

[Unclenick]

Dave,

Thanks. I'm just a nerd engineer who's been pondering this stuff for a long time. Still learn new things all the time, too. My dad still has a 1939 Camp Perry patch on his shooting jacket, so it runs in the family.


Squareknot,

For a given powder and bullet and barrel length, peak pressure and velocity have a direct relationship. There is only so much energy in the powder. If it is expended earlier in bullet travel down the barrel, due to ignition conditions, the pressure rises, improving burn completeness and accelerating the bullet more early in its travel down the tube, so it has more time to pick up velocity from residual barrel pressure. So, your greatest velocity will be from the highest pressure load with a fixed charge. If you put a strain gauge instrument on the gun barrel, you will be able to verify that.

As SL1 said, primers are made with different cup thicknesses and material hardness, as well as different mixture brissance and fuel quantity, all of which affect how they appear after firing. So, you really can't judge relative pressure by primer appearance when changing primers. Every brand will have a somewhat different deformation response to any given load peak pressure.

One weird thing that happens sometimes is when a hotter primer actually gives a particular load a lower pressure and velocity. This is when the primer is too hot for the powder volume in the case, so it tends to happen more in smaller cases and more often with powders that have slow burn rates for the case volume (but not always). When it occurs, it is because the primer makes so much pressure that it unseats the bullet before the powder gets burning. That increases the volume the powder starts burning in and lowers net start pressure. The .22 Hornet is famous for needing extra mild primers like the Remington 6 1/2 for this reason. In short pistol cases it can be a problem even with non-magnum primers. In .45 ACP, for example, match shooters at the Nationals decades ago noticed military hardball was more accurate than commercial hardball. It was finally traced to the fact the military specs require molten bituminous pitch to be applied to the bullet to act as a seal. That glued the hardball in just hard enough to increase the start pressure and stop bullet unseating by the primer. It therefore improved ignition consistency.

You can achieve much the same effect by seating pistol bullets out to headspace the cartridge on bullet contact with the throat, rather than on the case mouth or, as is too common, the extractor. That increases start pressure and gives the primer nowhere to move the bullet significantly before the powder gets burning. But that also assumes a bullet shape and short enough throat that you can seat out that far and still fit the magazine and still feed reliably. With the higher start pressure, you may have to reduce your load. A chronograph is a good way to check that, as long as the powder and primer and case volume remain unchanged.

[DaveBeal]

I'm just a nerd engineer who's been pondering this stuff for a long time.

Birds of a feather. I'm a nerd engineer who's been pondering it for a short time.