Good Morning Everyone,
Thought id take a stab at contributing something useful to the forum here. You all have put so much info on here that it's like a library. I am happy to take any constructive criticism and adjust my method (or this writeup) accordingly.
I've been hand loading for 15 or so years to some extent. Mostly pistol, but some rifle now and again. I do not claim to be highly knowledgeable in this area, although i have done it quite a few times and i'm pretty comfortable recommending things like this to others.
With the short leade in these CZs we all know and love, I need to get a good load matched up to my barrel. That's made more difficult by my desire to load heavier bullets. I really enjoy the way 147s feel when loaded to approximately 130PF. I keep my rounds at about 870-900 fps for about 133pf.
Enter the rocky mountain (RMR) 147 grain match winner bullet. It's a flat point I've loaded up previously for subsonic suppressd shooting. I like the accuracy and the nice round holes it makes in paper.
Here's how i calculate the proper OAL to use based on this specific bullet type:
Step 1, initial check, check that your current loads pass the plunk test. Remove the barrel and make sure it's clean and dry. I like to use 91% isopropyl alcohol and bore brushes. Scrub it down to make sure it's spotless. Hold the barrel vertically, with the muzzle end down. Drop the loaded case into the barrel (makes a plunk sound). Flip the barrel (muzzle side up) and drop the round out. If it drops out, you're halfway there. If not, the bullet is very likley touching the rifling and is too long. If it does drop out, i prefer to reinsert the round again, and see if i can spin it gently with my fingers. This is redundant in most cases, but it's how i like to second-check my work. To check for how it should feel you can also use a clean and resized case with no bullet to spin. Put that empty brass case in the chamber and give it a spin. No resistance is what you're going for here.
If your rounds are good, i recommend loading one longer, to build in a margin of safety. As i've read around, go 0.015" longer than your expected OAL. Repeat the plunk test above. If that longer round drops freely and spins freely, your load is good to go and you can proceed in mass-producing it.
Please be mindful, here, that changing OAL will probably change your velocity. New OAL will ned a new chrono test to make sure it's doing what you want it to do.
Step 2, if the plunk test fails or you're starting from scratch, i'd start here. Load some dummy rounds at various lenths. I'd recommend starting where you want to load. For example the loading manual recommended load. Check SAAMI specs here too, to ensure you're not over or too far under. Too far under will cause feeding issues with some barrels in my experience. Too far over and the rounds won't fit in the magazine. be careful with any oddly molded bullets too, here's an example of a rounded one. This rounded tip would give a higher OAL reading when measured, but the seating die doesn''t touch that area, so the bullet is actually a tiny bit deeper in the case.
First, size some brass, same headstamp if you can. Then flare the mouth if needed. Use a single stage press or use your progressive one stage at a time do accomplish this. Load some rounds with your bullet seater set way out longer than you'd intend to load. I load at about 1.160 or longer. Then set your seating die to just touch the bullet. Crank the seating die adjustment an 8th or 16th rotation at a time and measure OAL each press. Get the round to your desired length and lightly crimp as you would a loaded round. recheck the OAL and label the round (i like the fine tip sharpie for this). Then load another until you have a set. I like to have a set in increments of 0.005 so i can test all my barrels (i have a few CZs)
After the rounds are loaded to the predetermined lengths, crimped, and labeled, I highly encourage checking in a gauge. Hundo gauges are a tad loose for me, so i use a wilson or lyman. Mine here is a lyman. Make sure they fit the gauge and triple check OAL before using as your " chamber leade gauge".
Once you have a set made up, plunk shortest to longer until you get a failure. At that point, back it off until you get one that drops and spins freely. Subtract 0.015 from that OAL and proceed with chrono testing, accuracy testing, and ultimately mass-production. You'll want to chrono your loads at this OAL and determine what powder load you are going to use before loading hundreds or thousands of them as well.