A collection of links to older, reloading data PFDs A tip-of-the-hat to 24hourcampfire
Posted for historic reasons.
It is interesting to see how much reloading data has been reduced over time. For example, one early manual suggested that 5.7 grains of Unique and a 158gr, cast lead bullet was OK. The current Alliant Powder manual now lists 4.7 grains of Unique for that bullet. That is almost an 18% reduction in powder.
It is my opinion that better and less expensive instrumentation is the reason, not "lawyers" or changing powder formulation.
In general, the companies that produce projectiles tend to have more "conservative" data then companies that produce propellants.
Speer reloading data, historically, tends to be high. Hornady, Nosler and Sierra tend to be more conservative and in closer agreement.
The SAAMI Standards for pressure include something they call "Maximum Probable Lot Mean" and they define a way to calculate it.
A powder that performs extremely uniformly is "allowed" a higher loading than a power that has more variation.
Suppose you had a powder that flowed well and one that had a tendency to bridge and have "caves" in the measured volume. You could run closer to the edge with the powder that flowed well.
Now, suppose you were the company that produced the coarse powder that bridged. There is nothing in the SAAMI procedures that prevents you from WEIGHING every charge. That would shrink the variation tremendously and allow you to publish higher charge-weights AND VELOCITIES than if you had measured by volume. You would still be compliant with SAAMI standards even though very few reloaders go to the trouble of weighing every charge (and almost no, high volume handgun loaders do).
If you sold projectiles, you would collect all of the commonly used powder measures and sort through them to find the one most vulnerable to bridging and voids. Then you might mimic a distracted reloader, tapping some powder drops and not-tapping others to maximize measured variation. Then you would let the data tell you the maximum "allowable" load for each powder and projectile you sell. After all, you don't care if the reloader choses Titegroup or 800-X.
Back to instrumentation
Today, it is a snap to set up the equipment and let the software calculate the MPLM. Back when many of these manuals were written, copper crusher-pellets were used and collecting data was slow, tedious and fraught with error. It was tempting to discard data that did not follow simple, smooth trends.
The other thing about today's data is that it can produce a pressure trace as the bullet travels down the barrel. The technician can see phenomena like double pressure spikes and the like.
|A typical, un-filtered data trace.
One issue that is not addressed by SAAMI (as far as I can tell) is the filtering on the electronic instrumentation. Filters are a big, big deal. My gut feel is that companies that publish data are now using less aggressive filters and including excursions that earlier efforts would have filtered out.
There are two reasons why they would do this. For one thing, the equipment is capable of reliably capturing those excursions. The other reason is that attorneys can now afford to hire labs to replicate the load-development process. When challenged in court, the party that published the original load-data needs to be able to present a credible reason for discarding (filtering) data as much as they do. The fact that steel is ductile and a very forgiving material (in general) isn't going to save the powder or bullet company's bacon.