January 11th, 2018

Why Does Load Data Vary Between Reloading Manuals?

load manual sierra reloading hornady data

Written by Sierra Bullets Ballistic Technician Duane Siercks
One of the first things new reloaders notice is that load data varies between reloading manuals. The Sierra Bullets Technicians frequently get inquiries asking us to explain why the load data appears to be inconsistent. This article explains five key factors that can influence published load data.

Example of load data variances for two 168 grain bullets:

Sierra Reloading Manual Hornady Load Reloading

Here are five reasons why the load data varies:

The Bullet
Basically, the similarities in the .30 caliber 168 grain Match bullets (for example) end with weight and diameter. The bullets likely have dimensional differences such as bearing surface length. Bearing surface has a large effect on pressure and velocity. There are also differences in boat tail, flat base, ogive and over-all lengths, which each help determine the cartridge over-all-length (COAL). With different COAL’s, we can expect changes in pressure and velocity also. In some calibers there are differences in bullet diameter with different bullet manufacturers.

It is also worth noting that bullet manufacturers do not all use the same copper alloy for their jackets. This produces more or less friction that results in load pressures and velocities. The solid copper bullets also vary quite a bit in comparison to a lead core and copper jacketed bullet.

The Gun
Each gun is unique, even if you are using the same make, model, and caliber. Special consideration should be used to consider that not all firearm chambers are the same either, creating more variables that need consideration. There can be drastic differences in the throat length. This controls the amount of “jump” that a bullet experiences when the cartridge is fired.

The Powder
Within normal manufacturing tolerances, you can see some variation in a given powders burn rate between different lots of the same powder. So naturally when two different Manuals are produced, it would be doubtful that the same lots would be tested.

The Cartridge Cases
New cases are almost always near minimum specs in dimension. A load fired in a new case would likely have slightly more pressure that when fired in a re-sized case. This would certainly be true if we were loading into fire-formed cases that have had minimal re-sizing done. Fired cases that are full length resized most of the time be slightly larger than the new unfired cases. This gives you differences in case capacity. The same powder charge placed within a new case and a full length resized case will produce different pressure levels and probably different velocities.

Conditions
Temperature can cause pressure increases or decreases. Hot temperatures tend to cause pressures to increase, while cold temperatures will usually do the opposite. Humidity and altitude can impact pressures and velocities likewise.

Conclusion
As you can see, an amazing number of variables effect any load combination. With the differences in the manuals, you’re just seeing firsthand examples of what took place when the data was collected with that particular set of components and firearm. Think of a reloading manual as a report. In essence, a reloading manual says, “We tried this particular component combination, and these are the results we obtained.”

Remember that you may or may not reach the same maximum load safely. There is no “one load fits all bullets.” The minimum load data offers a safe place to start. The maximum load data listed should always be regarded as a safety guideline and not necessarily a goal! Your gun should shoot accurately without breaching the maximum load data. The best advice is: always start low and work your load up!

If you have questions about variances in load data or other reloading questions, please call our ballistic technicians at 1-800-223-8799 or send us an email at sierra [at] sierrabullets.com.

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March 3rd, 2017

Inspecting Your Brass — What Case Flaws Reveal

Case Diagnostics 101 Sierra Bullets .223 Rem 5.56 brass cartridge safety

Ever wondered what caused a particular bulge or marking on a case? And more importantly, does the issue make the case unsafe for further use? Sierra Bullets Ballistic Technician Duane Siercks offers some insight into various issues and their causes in this article from the Sierra Blog.

Incipient Case-Head Separation
This is a Winchester .308 Win case that has a real issue. This case has a very obvious incipient case head separation in the process of becoming a complete failure.

Sierra Case reloading pressure safety inspection

This is most commonly caused by over-sizing the case causing there to be excess headspace on the case. After a few firings and subsequent re-sizing, this case is just about ready to come completely apart. Proper die adjustment is certainly a requirement here. Of course this case is not safe to reuse.

Excessive Pressure (Load Too Hot)
If you will notice in the picture of the case rim, there are two pressure signs to notice. First, look at the primer. It is basically flattened to about the max of what could be considered safe. If this was the only pressure sign noted, I would probably be fine with this load, but would constantly keep an eye on it especially if I was going to use this load in warmer temperatures. This load could easily cross into the “excess pressure” realm very quickly.

Sierra Case reloading pressure safety inspection

There is another sign of pressure that we cannot ignore. If you’ll notice, there is an ejector mark apparent that is located over the “R” of the R-P headstamp. This absolutely tells us that this load would not have been in the safe pressure range. If there were any of these rounds loaded, they should not be fired and should be dis-assembled. This case should not be reloaded.

Split Case-Neck
Here we have an R-P .22-250 case that has died the death. Everything looks fine with this case except the neck is split. This case must be tossed.

Sierra Case reloading pressure safety inspection

A split neck is a normal occurrence that you must watch for. It is caused by work-hardening of the brass. Brass cases get harder with age and use. Brand new cases that are stored for a period of time can become hard enough that they will split like this case within one to two firings. I have had new factory loads do the same thing. Then as we resize and fire these cases repeatedly, they tend to get harder and harder. Eventually they will split. The life of the case can be extended by careful annealing practices. This is an issue that would need to be addressed in an article by itself. Of course this case is no longer usable.

In the classes that I teach, I try to use examples like this to let the students see what they should be looking for. As always, if we can assist you, whether you are new to reloading or very experienced, contact us here at Sierra Bullets by phone at 1-800-223-8799 or by email at sierra@sierrabullets.com.

Dented Case Body
Here we have a Lake City 7.62×51 (.308 Win.) case with two heavy marks/dents in the case body.

Sierra Case reloading pressure safety inspection

This one may be a bit of a mystery. It appears as if this case may have been caught in the action of a semi-auto rifle when the firearm jammed or the case failed to clear during the cycling process. I probably would not reload this case just to prevent any feeding problems. This also appeared to be a factory loaded round and I don’t really see any pressure issues or damage to the case.

CLICK HERE for MORE .223 Rem Case Examples in Sierra Blog

It is very important to observe and inspect your cases before each reloading. After awhile it becomes second nature to notice the little things. Never get complacent as you become more familiar with the reloading process. If ever in doubt, call Sierra’s Techs at 1-800-223-8799.

Sierra Bullets Case Diagnostics Blog

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