Mr McLeod -
There are 2 major factors for chamber pressure:
amount of powder and
case volume under the bullet. We talk a lot in terms of "OAL", but what really matters is
OAL minus bullet length. Since the manual writers didn't know your particular bullet length, the loads in the book are only a report of what worked for them. Your results will almost ALWAYS vary. Therefore, some answers may take extra work to get. Such is your case.
Your 4.3gr load at 1.145" is way too light. The volume of powder is up there, but you've extended your OAL enough to (in effect) knock it back down. The black interior of your cases says so. The black burn marks around the case mouth say so. And the rounded primers say so.
There are 2 things you can do.
• You can shorten your OAL in .010" increments (1.135", 1.125", 1.115", etc) down to 1.075" or until the interior of the cases starts to run clean (gray or tan color).
• You can start adding more powder. However, since you know you're in the warning area (at least on paper) only increase it in 0.1gr increments. (ie 4.3, 4.4, 4.5gr.)
Choose one or the other and go slowly. The efficiency curve for powder is NOT a straight line. When you get close, it will get
REALLY good very fast. It's a lot like looking for a new address. You can drive 70 MPH to the general area, but then you have to slow down to 30 MPH when you're in the neighborhood.
Load only 6-10 rounds at each new load and start with the longest OAL or least powder. Study all the fired cases before moving to the next step. When you find the gray color and the flatter primers, then
STOP. Disassemble all the remaining un-shot rounds.
Do some research here on "pressure signs". Here's one of my favorite photos. You want yours to be like the one in the middle....
Hope this helps!
