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Old December 24, 2012, 02:18 PM   #1
leadchucker
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Bullet variations make much difference?

FMJ vs TMJ. FMJ RN vs FMJ FN. FMJ vs JHP. Given identical bullet weight, do these differences make much difference in powder charge, starting or maximum loads?

The reason I ask is that I never seem to be able to find load data on the exact bullet I want to load. I'm always having to put a little guessing into it.
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Old December 24, 2012, 06:18 PM   #2
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Yes they make a difference. Sometimes a very big difference depending on some factors such as jacket thickness, coatings, or total bearing surface.

Pick the data for the bullet type closest to the bullet you are trying to reload, but heavier. Then reduce by 10% and load up, or start at the starting charge if there is one listed. I've been doing that for a long time now and haven't had a blow up yet.

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Old December 24, 2012, 06:33 PM   #3
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In general, if you have data for a bullet of similar construction (i.e., jacketed, cast, plated, solid copper) but of different shape, the loads will work if you can use the same seating depth and still have the round fit your magazines and feed properly.

Seating Depth = Nominal Case Length + Bullet Length - COL (Cartridge Overall Length)

Use that formula with the known load (you may have to call to find the bullet length if you don't know it; there is also a partial list, here) to learn its seating depth. Once you have that, then rearrange the above formula to find the COL you need with your different length bullet to get the same seating depth:

COL = Nominal Case Length + Bullet Length - Other Bullet's Seating Depth

If the other bullet, loaded to that new COL does not fit your magazine or feed, you are going to have to reduce the charge and seat a little deeper. Basically, you want to keep the percent of the empty space occupied by the powder underneath about the same for the new load. So if your deeper seating depth reduces that space by 10%, then you want to reduce the powder charge about 10%. This doesn't work perfectly, but it's a good approximation to start with.
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Old December 25, 2012, 05:28 PM   #4
leadchucker
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Bullet seating depths or bullet lengths are not included in any load data I've seen. And finding the actual dimensions of the bullets used in the load data is proving to be a problem sometimes.

Seems to me that knowing bullet seating depth or bullet length would take a lot of guesswork out of working up loads.
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Old December 25, 2012, 05:49 PM   #5
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Leadchucker,

What bullet in what cartridge? Folks here can be quite helpful when given specifics.

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Old December 25, 2012, 06:25 PM   #6
leadchucker
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For example:
I currently have a stock of 9mm 125gr RN FMJ bullets.
The book I usually rely on, Lyman's #49 lists a 9mm 124gr JHP. Probably a good match... IF I can figure out a reasonably accurate OAL. Unclenick's information on calculating OAL/seating depth is exactly what I needed to know, and I can calculate the OAL for my round nose bullets, IF I know the actual length of the JHP bullets used in the load data.

JBM ballistics lists at least a couple of 9mm 124gr JHP bullets, depending on what brand you're talking about. I have no idea what bullet the Lyman data is based on. The best I can do is make a closest guess, and err on the conservative side. In doing this, it seems I'm always winding up with starting loads that are waaaay too light. I'm sure that this is in part caused by conservative seating depth. I'm just trying to eliminate some of the guesswork.

Win231, if it makes any difference.
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Old December 25, 2012, 06:32 PM   #7
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In pistol FMJ's are a little different than JHPs, the FMJ's have a "naked base" which is more compressible than the solid copper base of a JHP (reverse drawn jacket). This matters a lot more in rifle than pistol though.

This is from Hodgdon for 9x19, which I assume is what you meant by 9mm.

125 GR. SIE FMJ Winchester 231 .355" 1.090"
4.4 1009 24,600 CUP 4.8 1088 28,800 CUP

Hope it helps.

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Old December 26, 2012, 10:06 AM   #8
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Quote:
Bullet seating depths or bullet lengths are not included in any load data I've seen.
Right. That's why I gave you a formula to calculate it for yourself, and a link to bullet length data. Most manuals do have the trim-to length of the case that they used for the load and the COL they recommend for the bullet, and you just use those in the formula. If they don't give the case length, just use the standard case length listed by SAAMI. SAMMI gives you a minimum and a maximum, and trim-to length is usually just half way inbetween.

Manufacturers don't usually don't give bullet length in a manual, but calling or emailing will normally get it for you. If you're not confident about making the calculation, that's another reason to call or email the bullet maker. They should be able to tell you length and COL and may even provide a seating depth if you ask for it. In the case of Hornady, they'll even email you their recommended loads for their bullets. Some other makers may be doing that as well. It's worth taking the time to ask them if you are feeling uneasy about it.
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Old December 26, 2012, 10:28 AM   #9
leadchucker
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And I thank you kindly for the formula. I've resorted to that same calculation before to try to arrive at an acceptable OAL for some of these mystery bullets, but I just needed some confirmation from someone with more experience than I have that I wasn't doing something seriously wrong.
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Old December 26, 2012, 11:07 AM   #10
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Quote:
The reason I ask is that I never seem to be able to find load data on the exact bullet I want to load. I'm always having to put a little guessing into it.
Educated guessing and experimentation is the essence of being an hand-loader. It is what we do.
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Old December 26, 2012, 09:26 PM   #11
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There is an article in the latest Handloader Magazine (#281, December 2012)about the perils of bullet sustitution. It describes pressure testing experiments by Dr. Lloyd Brownell in the 1960s, where he was trying to produce equations to predict pressure, etc. from cartridge/gun/load parameters. He came across one situation where two bullets of the same caliber, weight, shape and construction TYPE produced VERY different pressures.

The troubling bullet was a 105 grain Speer roundnose bullet that looked to be about the same shape as bullets from Hornady and other manufacturers. However, it developed much higher pressures. Substituting that Speer bullet in data for the other bullets could result in pressures of 125,000 to 163,000 psi. This result was predicted by the equations that he developed and then verified by actual pressure testing, so it is not just a theory.

Speer explained the behavior of their bullet as being due to thicker jacket walls, stiffer heels, and long caliber diameter section than bullets of comparable weight.

How many of us can look at bullets and tell how they will behave under pressure?

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Old December 26, 2012, 09:29 PM   #12
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The main thing is how much bearing surface the bullet has and how much case capacity it occupies. For example, If I had data for 140grain spitzer, I would have no problem using that data for a 140 gr spritzer boat tail. If I were using boat tail data for a spitzer, I would work up from starting load.
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Old December 27, 2012, 02:35 PM   #13
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Good point from SL1. When the admonition of same construction for substitutes is given, it can be more stringently literal than some suppose. This is why, even after finding a matching seating depth, using a 10% lower starting load and working up over again is important, with H110/296 being a singular exception (though its normal peak pressures are already lower than many other powders used in the same applications).

Also, if anyone is interested in the Brownell study, it is available here.
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Old December 27, 2012, 10:09 PM   #14
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Unclenick, I have been mentioning the importance of taking note of the volume under the bullet (and observing that COL/OAL/COAL is a proxy for that measurement) and see that the formula you posted is a lot simpler than my (too wordy) explanations. Thanks for that.

Do you think that web thickness has an appreciable effect on the case volume and do you think that dimension should be taken into account or would that be gilding the lily?

I have marveled at your expertise and wisdom in the past and never thought to ask this question until now.

Thanks.

Lost Sheep

p.s. Seating depth is a useful term all right. (Distance from the base of the bullet to the mouth of the case and pretty much tells you how much contact is being made between the inside of the case and the side of the bullet, which is nice to know.)

What term describes the distance from the top surface of the web of the case to the base of the bullet? Is there one?

Last edited by Lost Sheep; December 27, 2012 at 10:23 PM.
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Old December 28, 2012, 09:37 AM   #15
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"FMJ vs TMJ. FMJ RN vs FMJ FN. FMJ vs JHP. Given identical bullet weight, do these differences make much difference in powder charge, starting or maximum loads?"

The nose configuration has no effect on powder charges. Construction and seating depth/burn space will matter but not very much unless you're loading on the ragged edge of a KABOOM. Starting loads are intended to be more than safe for any bullet or firearm type. Normal 'work-up' in small steps will take care of establishing a rational max charge. As we approach excessive pressures in a handgun an attentive shooter will be aware of harder than normal recoil that will batter the piece without shattering it immediately IF the reload development is being done correctly.

IF we really needed bullet specific loading data for every bullet made there are a LOT of bullets we couldn't use because no one does book development for such individuals. That's because it isn't necessary, just use normal book data for the bullet weight and general type (jacketed/cast) you're using and go.

Good luck!
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Old December 28, 2012, 10:02 AM   #16
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1-the bullet seating depth is dependent on a specific bullet shape, how a specific pistol chamber is cut and what length your mag needs. In all cases you should load up a dummy round to ensure you are not jamming the bullet into the rifling, it feeds from your mag ,is not being crimped on a undersize diameter portion of the bullet and is does not have excessive setback.

2-Bullet nose shape and general overall bullet shape can make a significant difference in powder charge. There is a considerable col difference between 115 jrn, Sierra's or Nosler's 115 jhp and Hdy 115 xtp. This leads to differences in bearing surfaces and available volume for powder. The nose shape of Winchesters 115 fmj lets it be seated out further than some others.

3-There are several loadbooks that list COL, but you still need to determine what works in your pistol.
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Old December 28, 2012, 11:25 AM   #17
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Lost Sheep,

I don't know of a specific reason for locating the interior bottom of the case because case walls aren't all designed the same. When I emailed Starline to find out if their .357 and .44 Magnum brass was identical to their .38 Special and .44 Special brass except for length, they said no. They make the walls of the magnum cases thicker near the head. So, if you seated the same bullet the same distance from the web in one of their Special cases and in one of their Magnum cases, you'd have a little more powder space under the bullet in the Special, and that space is what affects peak pressure.

The best bet you have for matching pressures is to find the actual case capacity under the bullet. Weigh a fired case, then fill it with water, push a bullet in to your usual COL (squirting water all over in the process), then remove the bullet and wipe off the outside of the case and weigh it again. The difference in weight is case water capacity in grains for your load and it is really that number that you want constant for same-weight, same construction bullets bullets with the same primer and powder charge.

There's a methodological caveat to the above, which is that lower pressure loads (below 30,000 psi, roughly) will often have their peak pressure depend on resized case capacity more than expanded (as-fired) case capacity. In the instance of making case measurements for a lower pressure load, you can seat a bullet into a resized case, weigh it, then use a glue dispensing syringe to fill it with water through the flash hole, and weigh it again (keeping it upside down to avoid spillage) to find the case water capacity. Case water capacity is distinct from case water overflow capacity; the former being water capacity in grains under the seated bullet, while the latter is water capacity in grains when the case is filled level with the mouth of the empty case. QuickLOAD uses the latter and bullet shape and seating depth to calculate case water capacity, and that calculator is a third way you can get the measurement.


Quote:
Originally Posted by wncchester
The nose configuration has no effect on powder charges. Construction nad seating depth/burn space will matter but not much unless you're loading on the ragged edge of a KABOOM. Starting loads are intended to be more than safe for any bullet or firearm type.
Nose configuration can affect seating depth and that affects powder charge. Sometimes a lot. I'm thinking, as an extreme example, of a 148 grain .38 wadcutter that has to be seated flush to the case mouth to feed in the Smith '52 or into a .357 self-loader or into some lever guns, verses a nearly same-weight 150 grain round nose bullet that sticks out and leaves a lot more powder space underneath.

Construction can also matter a lot. Reread SL1's second paragraph in post #11 above for a lab measured example.

While some manuals have very low starting loads that would do what you say, I think what you see most, as with Hodgdon's data, are starting loads that are only about 10% below maximum. That creates a 20% to 30% reduction in peak pressure, depending on the cartridge and components used. That's only just enough to compensate for the measuring errors that copper crushers can produce for identical components. You don't get the extremes often, but I've twice run into starting loads that were already at or near maximum in a particular gun, despite using matching components to those the manual author did.

Below is an example that's on page 119 of the SAAMI centerfire rifle standard. They sent cartridges from the same lot of M1 Carbine reference ammo to nine different facilities for copper crusher testing. They all agreed on velocity pretty well (about 3.5% difference), but got over 23% different peak pressure averages. So just about what a 10% charge would compensate for if the error were a 23% low reading of what was actually operating at the SAAMI MAP. In that instance the staring load would be at SAAMI MAP and the max load on the list would be near the proof load range, with some individual rounds occasionally exceeding the proof range if SAAMI's assumed 4% standard deviation is used.

The more modern conformal Piezo transducers that give you psi instead of CUP are about twice as tight, so if you have data you know is Piezo transducer tested, then you have a little more wiggle room, but not necessarily enough to cover a bad combination of component swap outs.

Anyway, the bottom line is that starting loads in data can be low enough only for starting with matching components. An example is the .243 Winchester with 85 grain bullet. In the Nosler Manual with their components the maximum load of RL19 is 43.5 grains. In the Speer manual for the same bullet weight the starting load of RL19 is 46 grains and the maximum is 48 grains. The Speer starting load is not adequate for a change to the Nosler component combination unless you don't mind stressing your gun unnecessarily.

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Old December 28, 2012, 09:22 PM   #18
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"Nose configuration can affect seating depth and that affects powder charge. Sometimes a lot. I'm thinking, as an extreme example, of a 148 grain .38 wadcutter that has to be seated flush to the case mouth to feed in the Smith '52 or into a .357 self-loader or into some lever guns, verses a nearly same-weight 150 grain round nose bullet that sticks out and leaves a lot more powder space underneath."

True as you state it. But, the question is how much does it matter? Sticking with your example, lead bullet charges are normally significantly lighter than jacketed, especially so for deep seated wad cutters, so unless the load is on the verge of blowing up the differences in actual practice tends to be meaningless.

For full power jacketed loads a small seating depth change means very little EXCEPT for hot loaded 9mm and 10mm loads and that's because they have very small burn cavities, they use very fast powders and the bullets are typically seated very close to or in the lands. That's not true for most auto cartridges, and no revolver cartridges at all, so they aren't nearly as twitchy as the 9s and 10s. Even then the slight seating adjustments required for proper feeding of different nose configurations aren't great and not all of them can be fed through many autos anyway. Those which do matter can be corrected by dropping maybe .2 or .3 gr. of powder and normal load work up.
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