OK
Take 5 brand new cases and load them to you current 'max' load, load and fire them 5 times.
Write down velocity of each round fired.
-are the primers still tight?
If they are, go up 1/2 grain and do over.....velocity should be a little higher, WRITE IT DOWN!
-are the primers still tight?
Keep going up until you get loose primers
This VELOCITY is over-max for YOUR in this gun/barrel/setup.
Once you've loosened the primers, throw those cases away, (((or,
if you're a COMPLETE tightass like me, seat the primer with a
cigarette paper and slop fingernail polish around the joint, load
with a moderate varmint load and bring it hunting, eject it into the bush!)))
Back down one full grain, check velocity and check the primers....
YOUR MAX VELOCITY, regardless of any book, any guesstimate from some feller on the innertube, any formula or software program, any app or download, is
1 grain below where your primers get loose. Now, the reason you need to write down the velocity is because velocity is the result of pressure. (You will get guys who argue this point, ignore them unless you're willing to burn up several barrels TESTING this concept) and pressure varies with temperature, soooooo....... IF you're going to play around with MAX loads you MUST understand that PRESSURE CHANGES WITH TEMPERATURE!!!!!
Write that down
Those loads you worked up in July may just LOCK YOUR GUN UP in December!!!
MAXIMUM LOADS ARE TEMPERATURE SPECIFIC
You MUST find your maximum velocity and then you MUST stay well below it whether it's 0 degrees or 30 degrees outside
If you can't/aren't willing to/won't test this stuff for yourself, stay away from maximum loads. For a maximum year-round load work up to loose primers and back off 2 full grains, this SHOULD keep you out of trouble thru the year.
Here's what I ask my Hunter Ed kids....
"What's the difference between this 243 cartridge and a hand grenade?"
Answer
"You'll probably never detonate a hand grenade 8" in front of your right eye!"
And BTW, to answer your question within a question, I jump 1/2 grain increments when using a powder thrower (measure) for a bunch of reasons, the main one being that you are fooling yourself if you think your measure can advance in .2gr increments, it can't. If you want to get serious about this then get a 500.00 scale and weigh your charges, graph EVERYTHING for velocity and weigh down to the kernel of powder and you might re-adjust your max a little tighter..... meantime just fuh'geddaboudit, stay away from max. FIND IT, scientifically FIND MAX, and then back off.... Go up and when primer pockets loosen, BACK OFF!
The case is your gauge, when it fails, YOU'RE DONE
back the load down
and if you want to predict WHEN the case will fail, use a chronograph.
And BTW this is scientific. It's the RIGHT way to do it. You can read books, you can talk with "techs," you can talk with people who work at large reloading/testing facilities, you can learn about CUP's and LUP's and PSI's and test cylinder plunger setups......you can learn about strain gages, you can BUY strain gages, you can buy a strain gage/oscilloscope setup if you so choose.....you can buy a blade mic and "measure for casehead expansion" but in the end you will learn that THE MOST ACCURATE method of measuring is gauging. Which is exactly what you're doing with those primer pockets....
YOUR gun, YOUR sizing method, YOUR chamber/headspace/tenon/lube/case phizzick and YOUR primers/powder/bullets will tell you the story.
Loose Primers=Too Hot
The End
al
