Effect of different bullets on ballistics/pressure

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KenFromNY

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Disclaimer: I am relatively new to reloading.

I've been successfully reloading 38 special with Trail Boss and was looking to try out an HP-38 recipe. I have two different brands of bullets, XTreme and Acme, both 158gr SWC. I went to the Hodgdon reloading site and checked out load data for HP-38. The results were somewhat surprising. (If the cut and paste doesn't show up well, you can just repeat my results at https://hodgdonreloading.com/reloading-data-center : 38 special, 158gr, HP-38.)

158 gr cast LSWC
Manufacturer Powder Bullet Diam. C.O.L Grs. Vel. (ft/s) Pressure Grs. Vel. (ft/s) Pressure
Hodgdon HP-38 BUY NOW 0.358" 1.475" 3.1 782 11,900 CUP 3.7 834 14,600 CUP

158 gr Hornady XTP
Manufacturer Powder Bullet Diam. C.O.L Grs. Vel. (ft/s) Pressure Grs. Vel. (ft/s) Pressure
Hodgdon HP-38 BUY NOW 0.357" 1.455" 3.8 661 12,600 CUP 4.3 779 15,900 CUP

The first thing I noticed is that the max charge for the LSWC (3.7gr) is less than the minimum charge for the XTP (3.8gr). Conversely, the max velocity for the XTP (779fps) is less than the minimum velocity for the LSWC (782fps).

One theory I had is that the larger diameter of the LSWC vs the XTP (.358 vs .357) and lead being not as slick as copper causes the LSWC pressures to build much higher compared to an equal weight copper bullet and therefore less powder is needed to achieve the same pressure (and velocity). Is this correct? Is there anything else going on here that I'm overlooking?

Of course, the golden rule of reloading has been drilled into my head: start low and work your way up. But the physics of what's going on with this published data is very interesting to me if anyone can enlighten me. Is it likely that my Hitek coated Acme bullets would more closely mimic the LSWC and the copper plated XTreme would be akin to the XTP?

Thanks,
Ken
 
Typically, it is not desirable to drive cast bullets as fast as jacketed bullets. The XTP is a high-performance SD bullet, and requires velocity to expand, the cast bullet does not. There are pressure considerations as well.
 
KenFromNY said:
I am relatively new to reloading.
Click to expand...
Ken, welcome to wonderful world of reloading.

KenFromNY said:
One theory I had is that the larger diameter of the LSWC vs the XTP (.358 vs .357) ... causes the LSWC pressures to build much higher compared to an equal weight copper bullet
Click to expand...
There are several reloading variables (As well as shooting variables) that can effect initial chamber pressure build and average/maximum pressures. Diameter of bullet is one of them but there are other factors.

KenFromNY said:
Is there anything else going on here that I'm overlooking?
Click to expand...
Yes - https://www.thehighroad.org/index.p...-and-discussions.778197/page-10#post-10966692
  • Bullet hardness/softness vs bullet base deformation
  • Bullet's ability to seal with the barrel
Copper plated, coated and jacketed bullets are essentially lead/alloy bullets with full length gas check to reduce/eliminate leading of the barrel and gas cutting/erosion of bullet base from high pressure gas blow-by.

Larger sized lubed lead SWC bullet must deform the bullet base to seal with the barrel for pressure build not only for more efficient powder burn and more consistent pressure build but also to reduce leading of barrel (There is another action of bullet base deformation squishing the lube to form an "O" ring and lube "flow" to seal bullet surface voids but we won't discuss that here). Due to this, if you are reloading slower target loads instead of faster full power loads, use of softer lead alloy will help deform the bullet base better.

So lubed lead alloy SWC bullet (Say 12-18 BHN) sized .001" larger can deform the bullet base enough to require less powder charge to generate similar pressure levels. In comparison, although jacketed HP can use even softer lead core (down to 5 BHN), due to harder gilding metal jacket cup and smaller diameter sizing that allow more high pressure gas to leak around bullet base, higher powder charge is needed to expand the bullet diameter to seal with the barrel to generate similar pressure levels.

KenFromNY said:
Hitek coated Acme bullets would more closely mimic the LSWC
Click to expand...
Yes, this would be true and many reloaders treat coated bullets like lubed lead bullets where coating acts as lubrication.

KenFromNY said:
copper plated XTreme would be akin to the XTP?
Click to expand...
Not quite, depending on the thickness of copper plating.

"Regular" thickness plated bullet have average/around .004" thickness of copper plating and often rated to 1200 fps for copper plating failure (not accuracy) and should be used with lead load data. I found if I pushed regular plated bullets faster than mid range jacketed load data, accuracy starts to drop -
https://www.thehighroad.org/index.p...ng-at-25-50-yards.808446/page-3#post-10470195

"Thicker" plated bullets have anywhere from .006" to .015" thick copper plating rated from 1300 to 1500 fps and can be pushed faster/used with jacketed load data depending on plating thickness.

FYI, gilding metal used for jacketing will run around .020" - .030".
 
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Hooda Thunkit said:
Notice that Hodgdon doesn't continue up to the same pressure as with the XTP.

As for the XTP, isn't that a plated bullet?
Click to expand...

SD bullets are interesting in their own right. Take Speer's GoldDot bullet... they have a separate set of load data just for that bullet, vs their other bullets, plated or otherwise.
 
Charlie98 said:
SD bullets are interesting in their own right. Take Speer's GoldDot bullet... they have a separate set of load data just for that bullet, vs their other bullets, plated or otherwise.
Click to expand...
Speer Gold Dot HP (Like Speer TMJ RN) is thick plated bullet and have thickest plating I know (Best of my knowledge of around .018" thick) -
https://www.thehighroad.org/index.p...ng-at-25-50-yards.808446/page-3#post-10470195

So unlike other jacketed HP bullets that utilize gilding metal cup, the copper plating cannot separate from the lead/alloy core and can be driven to higher velocities with reliable expansion performance. Speer load data for TMJ/Gold Dot HP often list higher start/max charges - https://www.speer.com/reloading/handgun-data.html

BTW, I do believe, Winchester PDX1 bullets are also thicker plated.
 
 
The post above by LiveLife covers the bullet variables that affect pressure. The Hodgdon data in the OP illustrates how bullet construction alone can have a major effect on pressure (and velocity).
 
LiveLife said:
due to harder gilding metal jacket cup and smaller diameter sizing that allow more high pressure gas to leak around bullet base
Click to expand...

Thank you for the explanation. I definitely need to pay more attention to matching the recipe to the particular bullet! To highlight the differences from the published data: 4.3gr behind the XTP achieves essentially the same velocity as 3.1gr behind the LSWC. But the XTP load needs 15,900 CUP for this velocity vs. 11,900 CUP for the LSWC. These are big differences! Or looking at the data in another way, the max LSWC charge is comparable to the minimum XTP charge (3.7gr - 3.8gr), but the LSWC generates 14,600 CUP and 834fps vs the XTP's 12,600 CUP and 661fps. Once again, big differences, especially since energy is based on velocity squared.

Thanks all for the insightful comments.
 
KenFromNY said:
Of course, the golden rule of reloading has been drilled into my head: start low and work your way up.
Click to expand...

That's it, right there. No one here is measuring pressure, we are just watching for pressure signs. Some of us own a chronograph as well, and while those don't measure pressure either they can show when something is wrong with unexpectedly low or high velocities.

I always follow load data, and recommend you do too, but sometimes I have my doubts about its absolute accuracy. I have old books which show higher load data and newer books which show lower load data, both supposedly reaching the same pressures with the same powder. These are from the same powder supplier and while some loads change, some load do not so it's not like they updated all loads for all calibers with a certain powder.
 
Just as an FYI some data have the same bullets seated deeper with a different COAL and some bullet ogives are different giving the same or similar COAL than a different bullet but with a different or maybe the same max charge. Many variations on loads and data.

Sometimes seating depth matters more and sometimes less. It depends on the cartridge and powder used. Even primers with some loads.

My suggestion is the same that you will hear and read many times....start low and work up looking for pressure signs and only used published data sources. That is the safe way.

As time goes bye you will come to understand some of the nuances of loads and data getting a better sense of how some powders work, some cartridges work, bullets, and some data differs and why it does or doesn't.

Welcome to reloading, buckle up and enjoy the ride.
 
Watching for pressure signs is useful for rifle cartridges, but it is very unreliable for low pressure handgun cartridges like the 38 Special, 44 Special, 45 Colt, and 45 Auto. If you observe true pressure signs with those cartridges, you are way over SAAMI max pressure.
 
BBarn said:
Watching for pressure signs is useful for rifle cartridges, but it is very unreliable for low pressure handgun cartridges like the 38 Special, 44 Special, 45 Colt, and 45 Auto. If you observe true pressure signs with those cartridges, you are way over SAAMI max pressure.
Click to expand...

There is no point in pointing out a problem without discussing a solution.
 
BBarn said:
Watching for pressure signs is useful for rifle cartridges, but it is very unreliable for low pressure handgun cartridges like the 38 Special, 44 Special, 45 Colt, and 45 Auto. If you observe true pressure signs with those cartridges, you are way over SAAMI max pressure.
Click to expand...

NWcityguy2 said:
There is no point in pointing out a problem without discussing a solution.
Click to expand...

The problem is that people mistakenly "trust" looking for pressure signs for cartridges where it does no good and/or is dangerous.

BBarn correctly pointed this out.

The solution is primarily understanding the situation and using extra care and caution when loading for "lower margin guns" with SAAMI ratings below 35,000 psi.

Substituting bullets and thinking you can work up to a published max charge is not recommended unless you understand all of the variables that can increase pressure and your load does none of these things. Bullet construction and OAL (where it is actually load density that matters) are usually the biggest variables. For most bullets, less bearing surface, softer materials, circumferential grooves and slicker surfaces all tend to lower pressures. Lower load densities tend to lower pressures.

However, for the loads in post #1, the LSWC had more pressure and velocity at 3.7 gr than the XTP at 3.8 gr. This can be either one of two things. The two loads could have been developed at different times with different "batches", guns and test equipment. If so, the results of one or both loads may be "off". Alternately, the results may be "real" for the specific bullets and load densities tested.

To add to the confusion, there are two different Hornady 158 XTPs, one hollow point and one not. Quickload gives different predicted pressures depending on selection, but both are above SAAMI max at 4.3 gr of HP-38 and an OAL of 1.455". I have no idea of the bullet length for the LSWC used for the other load. A 0.660" long Lyman 155 LSWC loaded to 3.7 gr with a 1.475" OAL gets a Quickload prediction below the Hodgdon test results.

And going back to the opening post, it is commonplace to use cast bullet info for plated bullets. Given that the Hodgdon data at 3.7 gr for the LSWC was well below SAAMI max, this charge should be safe with the plated SWCs or the coated stuff.

I have other sources that would tend to indicate that up to 4.5 gr might be under the SAAMI max. However, these sources are again using traditional cast bullets instead of plated or coated.
 
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LiveLife said:
"Regular" thickness plated bullet have average/around .004" thickness of copper plating and often rated to 1200 fps for copper plating failure (not accuracy)
Click to expand...
And there is your answer: bullet failure.
A soft bullet pushed too hard will strip in the rifling like a screw torqued too hard in the threads. The harder the bullets skin and core, the more pushing it can take without stripping. Very hard outer skins allow for softer cores; but even the hardest outside has limits otherwise the bullet can strip the rifling.
The manufacturers rate their bullets for pressure and velocity. It’s not just pressure -or just velocity - it’s the combination of fit, material, pressure, heat, rate of expansion, and friction that determines the limits of a load. Fun stuff, eh? You’re going to enjoy the learning process. I can tell. :)
 
Hooda Thunkit said:
Hodgdon has historically shown lighter loads for lead. Some far lighter. I don't think it's a pressure issue, I think it's just a thing with them.

Notice that Hodgdon doesn't continue up to the same pressure as with the XTP.

As for the XTP, isn't that a plated bullet?
Click to expand...

Don't you know?

The Hornady XTP projectiles are jacketed bullets.
 
P Flados said:
The solution is primarily understanding the situation and using extra care and caution when loading for "lower margin guns" with SAAMI ratings below 35,000 psi.
Click to expand...

There is no such thing as "using extra care" when reloading. That's like patting yourself on the back not once, but twice.

An actual solution would be to use a chronograph.

P Flados said:
However, for the loads in post #1, the LSWC had more pressure and velocity at 3.7 gr than the XTP at 3.8 gr. This can be either one of two things. The two loads could have been developed at different times with different "batches", guns and test equipment. If so, the results of one or both loads may be "off". Alternately, the results may be "real" for the specific bullets and load densities tested.
Click to expand...

This is pure speculation, correct?
 
Using a chronograph and loading to a given velocity isn’t the best idea in the world. It’s not uncommon at all for numbers you read in a load manual to be unobtainable, safely, in every firearm so chambered.

We also know there are differences or variables that stack up when they are gathering data to put into load manuals.

For example we know that HP-38 and Winchester 231 are the same powders, made in the same place and are just sold under two different labels but it’s not difficult to find different data for them on the same page of a given load manual.

9198CF4D-7FF3-4950-8B60-4873A75A8BFC.jpeg

Same goes for H110 and W296.

A77DA368-572A-4AE0-8F9A-CC8D9CDF8011.jpeg

Lot to lot or environmental differences are two such variables but variables none the less, that could make your outcome different than theirs.

Then you have other variables like firearm or test barrel that can really change outcomes. If you are a guy that just keeps cranking the knob until you get to book velocity with your chronograph, you need to flip back and see what they used to obtain the data.

Trying to match book velocity with a 2, 4 or 6” 357 magnum might not be safe at all using the data from this book.

27147F58-54EA-477F-942B-0961CC59B411.jpeg

It’s also not uncommon these days for sources to omit what they used to gather their data.
 
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