Please read to the end because this will be quite extensive and it will help you irrespective of a caliber.
Maximum loads reference only pressure..velocity can vary.
I wouldn't rely on published burn rates. The charts are only an approximation. There's so many variables that affect the "mildness" of a load.
1. Your actual chamber dimensions, standards fall between min/max, minimum chambers usually max out with a load before a chamber on the maximum side of spec.(including leade)
2. Powder lot variation, again they fall between min/max. If you're lot is on the faster side you will reach max pressure sooner.
3. Bearing surface of the bullet, you can have 2 differing brands of bullets that weigh the same but they may have slightly differing bearing surface(ie VLD vs BTHP) and the one with more surface will generate more friction. More friction more pressure.
4. Brass lot/brand variation. Brass of the same caliber with more internal volume typically needs slightly more powder to hit max pressure than brass with less internal volume.
5. Primer variables
So you see while you might be able to detect a trend with only one of the variables, typically it's a much more complex relationship between allowing variables. If you were to have all of the above at the minimum specification and you just decided to load the top published loading you could very easily hit a dangerous pressure in your specific chamber.
Here's a short version of the best method I've found to use for determining a max load in your specific chamber without having to use electric strain gauges.(doesn't apply to accuracy, loading a ladder will-different topic) use of a chronograph with this method will aide in your determination but it's not absolutely necessary (I'll let someone else explain that aspect).
The method I use.
Keep good records of all your data.
1. Fire 7-10 factory loadings of the same lot , typically with the bullet weight you intend to load in your firearm.
Measure the head of each piece of fired brass then average it out. That average will be your maximum in your SPECIFIC chamber, but no other.
Start with a lower midrange published load with the appropriate components and powder. Use new brass. Load 5 rounds at each loading increment. The increments you choose to use will be dependent on case volume. .5gr in a .223 Rem has much more of an impact on pressure than .5gr does in a 300RUM. Only shoot one increment of 5 loads then measure before going to the next highest load increment.
Measure the 5 case heads and average. When you hit the average you got with the factory loadings, do not go higher, you are at maximum pressure for your specific chamber.
For instance my 1911 10mm my max is when the head measurement hits .4029, my friends Glock is .4032
If one variable changes, say for instance with powder scarcity you can't get the same lot next lb you buy—typically I start with my 3rd load DOWN from my max, and then I re do the upper increments from there re measuring the heads again until I reach that maximum baseline of head expansion determined from the factory loadings.
I hope this is somewhat helpful.
Regards. TO
