Different max loads for same weight bullets

[pinne65]

I am confused,

I'm looking at reloading data from different manuals. Same weight bullets have totally different min and max loads.
For instance with a Speer cast bullet, 45 L-SWC with Alliant Unique powder, min load 8.6 grains and max load is 9.5 grains. Muzzle velocity 891-941 fps. With a Hornandy bullet 45200 HP-XTP min is 6.2 and max is 7.1. Velocity 600-800 fps. Also with the Unique powder. Both bullets are 250 grains.

How can the min/max loads be so different?

Thanks for any info!

[versifier]

There are a number of different factors that can effect max loads in the books.
Every bullet is made with a slightly different alloy, cast or jacketed, and each has a different friction coefficient. The test firearm is different in every instance with differences in barrel size, steel used, etc. Then the brass is different in each test, with slightly different thicknesses and volumes, even if it has the same headstamp. All of these have a notable effect on actual chamber pressure.

It's a lot easier now that we have pizeo-electric transducers to accurately measure pressure. The old copper units as measured by the copper crusher method were relative values that showed a good amount of variation from test to test, even when all the variables were kept as equal as possible. That is why it is no longer considered safe to use older data. How much variation and how much the measured pressures differed from the actual pressures only became apparent when the modern method was introduced.

Also, there is a tendency to look upon "Max Load" as an absolute value. While the SAAMI designated max is a specific PSI measurement, safe max loads differ for each firearm. Some rifles will begin to show pressure signs on their fired brass at levels well below the max charge listed in a manual, while others will not begin to show them until the charge significantly exceeds the published max load. With pistols and revolvers, it is much harder to detect pressure signs on the brass, and consequently, much more important not to try pushing the limits with them. Many KABOOMS happen in them with less than listed max loads. There are lots of theories why, but no definite consensus.

Bottom line, the manuals provide a reliable guide. It's up to you to watch the brass in rifle loads for pressure signs as you approach listed max, and always work up from starting loads. Don't be tempted to push the limits with your handguns as you will get no warning when you have gone too far. If you think you need more velocity, move up to a bigger case with a higher working pressure. Stay safe, enjoy shooting, die of old age.

[runfiverun]

he is also comparing a lead bullit to a jacketed one
and your bearing length is vastly different with these 2 bullits.

if you want more velocity [ in the case of the hornady]
you will want to use a slower powder to develop more velocity safely.

[pinne65]

Ok,

Both loads as described in the original post were used and it went well. I figured it was safe since the jacketed bullet was listed for the lower load. And i started out with the min load for the lighter of the two. Worked my way up to max. Then tried min for the more powerfull load. And that's were I am right now. There were no signs, (as far as I can tell), of excessive pressure. The loads were fired with a Ruger Super Redhawk, casull. I will do practice some more on Colt 45 loads before I try loading for the casull though...

[runfiverun]

there are special loads for that srh
you can step that the colt up pretty far if you want to not as far as the casull
but near the 44 mag level.
with revolvers the best place [ that i know of] to look for pressure is
the primer area.