Why different formulas for same sort of bullet?

P

Prof Young

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Loaders:

Why are there different powder formulas for XTP bullets and jacketed bullets of the same weight? The XTP is a jacketed bullet . . .so what's the diff?

Live well, be safe
Prof Young
 
The single biggest difference is seating depth.

The space inside the case remaining for the propellant is highly critical. The deeper the seat, the smaller the volume, the faster the burn rate, the more quickly pressure develops.

So although a lot of data is interchangeable between bullets of the same weight, sometimes it isn't. For instance, Speer #14 has separate data for their 45 ACP 230gn RN from their 230gn GDHP's. The difference is seating depth.

Another example: For 38 Special, I use 148 DEWC's for all kinds of different applications. Well, there's very little load data for DEWC's. What I've learned is that 158gn LSWC data can be used, and it's far more common to find. Although the 148 is obviously 10 grains lighter than the 158's, they seat deeper, (deep seat, smaller case space, faster burn rate) and thus, cancel out the difference.

And then there is also just differences in the testing procedures, etc. when creating the load data between manufacturers. There's lots of variables.

Whenever I get a new bullet, I measure and record the bullet's seating depth. I want to know the case space difference between it and it's similar weight contemporaries.

I'm curious specifically what is your situation?
 
Even though they are the same weight, they may have slightly different shapes and one will have more surface in contact with the barrel. That bullet will require less powder to generate the same pressure.
 
One other reason is the data in the manuals are the test results they got with those components, that day, in that gun.

It doesn't mean some loads wouldn't work with other bullets of similar weights and styles.

It just means they used specifically what is listed to gather that particular data.

There are lots of variables in reloading, and manuals are a guide more so than a precise recipe for use in all guns.
 
Certain expanding bullets are made to deliver better terminal performance at certain velocities based on jacket thickness, how it is bonded, and core hardness.
 
Thanks

Thanks to all for the information. That all makes sense.

Nick - I was looking at the specific differences between 200 gn 44 mag XTP and 200 gn 44 mag jacketed. I've got a box of the xtp but not much powder that the charts say will work with them, but a lot of powder that's supposed to work with the jacketed.

Thanks for the information. So much to learn.

Live well, be safe
Prof Young
 
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Usually XTP or whatever premium bullet will have an recommended velocity range for best performance, usually the data is within that range, not to mention the oal like the above said.
 
I was looking at the specific differences between 220 gn 44 mag XTP and 200 gn 44 mag jacketed.
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I'm under the impression that the "200gn jacketed" is not an XTP? If not, specifically what is it?

I've got a box of the XTP
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Just for clarity, you mean the 220's?

but not much powder that the charts say will work with them
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What powder do you have? What is the purpose for these rounds that you want to load? What gun do you have? What barrel length?
 
Mostly it's about how the jacket stays on the core. HAP's for example are match grade bullets with no cannelure. XTP's have the cannelure. None of which matters in the least. You load for the weight.
Manuals are published test results. Manufacturer brings out a new bullet style, they test 'em. Jacketed is still jacketed.
"...specific differences between 220 gr 44 mag XTP and 200 gr 44 mag jacketed..." As daft as it sounds the answer is 20 grains, but there is no .44 220 grain XTP listed by Hornady.
 
If you search on line you can find some different results for tests done at different times. Rather than reiterate some of what has been said already, I'll direct your attention to this article on the subject by Alan Jones. It covers the bases pretty well. The main point is that if you go back to the 1960's, when most bullet makers used the same basic processes, bullets were more interchangeable by weight, and many load manuals only gave the bullet weight and type with their load data. Today, with many more specialty bullet makers and different processes and more special purpose bullets, that interchangeability has been compormised. Indeed, I have read older articles where bullet tests showed as little as 3% variation in pressure with jacketed bullet brands, and a later article with 8% difference found. It wouldn't surprise me if today you could find more, though I've not made the experiment myself.

The thing is to own a chronograph and if you have two bullets of the same weight and general construction, to shoot a few of each over the chronograph with the same starting load. I like to alternate between them so the bore condition tends to average out, then I separate the velocities manually into Excel on a tablet or cell phone for averaging. The one that goes faster is experiencing higher peak pressure, but if the difference in the two averages is less than the standard deviation of either string divided by the square root of the number of shots that string, I consider the difference likely to be random and don't change the load data. This isn't a very tight statistical test, but for a rule of thumb, it's good enough.
 
Ooops . . . .

I edited my last post above. It was 200 gr xtp not 220.
Sorry for the confusion. Big uncaught typo.
 
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The bottom line is that there is enormously flexibility in loads. It would probably be safe to substitute any identical component with proper precautions. If a load of red dot, for example, work s with a 125 xtp, with due caution nearly any 125 grain bullet of similar construction can be substituted. The very minor considerations such as jacket thickness or core hardness can almost certainly be offset by a reduction in powder.

It's best to follow data to the finest detail. Substitute a primer, a bullet, either one can probably be made to work, but it should not be assumed that a component can be tossed around Willy nilly at the same charge level without repercussions.
 
On the other hand, you do have some substitute loads that just shouldn't happen. A 158 grain .357 load cannot properly switch cast and jacketed. Changing a standard soft point rifle bullet for the Barnes solid copper bullets wasn't working so well. Take a shotgun round and fiddle ether wad, shot charge, primer, any of them, and the round may be totally screwed up.

It seems to me that shotgun rounds are probably the least adaptable of all reloading chores. There was a report that I read about bfennekke; the experimented with waxing the wars on their shotgun slugs. Waxing the wads led to numerous problems, including pressure deviations. The answer was to just leave off the wax and let the consistent bore friction be an asset, and not think of it as a problem to overcome.
 
Heh, now that we cleared the confusion and covered all the generalities, it would seem we're getting somewhere. :p

Just to kind of circle back: I measure and record the difference from the line where I seat the bullet (usually a cannelure or crimp groove), to the base of the bullet. If I run across two bullets with the same weight, but one seats deeper, I know that the one that seats deeper will likely have a slightly faster burn rate. For most applications, it probably won't matter much. But if I'm loading relatively hot with a fast powder, I may be compelled to drop the charge a bit with the deeper seated bullet.

Prof Young, I know you were asking a general question in your OP. But is there a specific loading you have in mind that has you scratching head? Sometimes the clearest way to answer a general question is to work with a specific situation.
 
The nice thing about generalities is that people like me who don't want to get really deeply into simple loads. there's a place for going for the best possible performance, and then there's the place for just putting together a few thousand rounds of stuff for shooting bulleyes with.
 
Prof young ... remember the load data you are reading is empirical data. It is what the tester got that day, at that time with the material listed. Nothing magical. Why the differences ? Simple different products, different temperature, different humidity, different test instrument condition, .... Rest assured your results will differ from the listed data no matter how hard you try to match the test results listed.
 
Empirical means observed at the time. Yes, that is correct.

When you have enough very small deviations from expected average and they lean towards better performance, you can find that performance is very significantly improved.

Picture the old guy with the black powder stump gun shooting at 1,000 yards. Powder a bit overly moist, irregular granules, in general just bad powder. He mixed bullets from three lots. Irregular stiff breeze from 2:00. cheap caps from different lots that he bought from a "friend."

Empirical observations can only be that either he or his rifle really suck, but only at that specific time. Both men and equipment can have "good days." Matching loads from five years ago that use different lots of all components, as well as different firearms, are VERY LIKELY to have different results. Follow that technician's example and empirically study your data and results, and use that information as your new, personal data.
 
Okay . . . let me be more specific . . .

Nick - Heres my circumstance that was the catalyst for the original query.

I have a couple hundred 200 gn XTP bullets in 44 mag. When I look at the load data charts, the powders they recommend for 200 gn XTP aren't found in my powder supplies.

When I look at the data charts for jacketed bullets in 200 gn 44 mag, I have all kinds of powder available. So I'm wondering why I can't use the formulas for jacketed bullets with the XTP bullets?

Any more thoughts?

Thanks again for all the info. So much to learn.

Live well, be safe
Prof Young
 
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