Those in the know will know...the only way to achieve this is if something goes wrong. Well, I got close (3785fps) and something IS wrong. Let me tell the tale.
I've been working up loads for my 257 Wby for several weeks. I've gone through four different powders and 3 different bullets, and shot about 200 rounds. About 2 weeks ago I figured I had arrived when I shot two consecutive, side by side 3 shot groups that you could have covered with a dime. As a matter of fact, even though there was 1/2 grain of powder difference between the two sets of three, had I shot all six bullets at the same spot you still could have covered the six-shot group with a dime. The magic combination was 72.5 grains of RL 25 behind a 110 grain Nosler Accubond, which yielded about 3550 fps. A little on the warm side, but no pressure problems. Although the Nosler manual lists no data for RL25 with the 110 grain Accubonds, it lists 72 grains of RL 25 as max for all of their 115 grain bullets. Since the data for the Accubonds is always the same as for their other bullets, I figured I was safe. And initially I was!
Before I started I was down to about 1/2 pound of the one pound canister of RL 25 I had purchased this fall, so I located another pound a few months ago and poured what remained of the "old" RL25 into the new canister. I was VERY careful to make sure I was not mixing two different powders, just two different batches of RL 25. I only ever put one kind of powder on the table at a time, and I carefully checked and rechecked the lables before, during, and after. I don't recall making any special effort to shake up or mix the two batches, but I may have since my intent was to have one fairly uniform batch.
I used about half of the RL 25 in the canister to work up loads for my 7RM, and then switched to the 257 Wby. No problems. Then, after shooting the two groups I loaded ten of bullets a 72 grains of RL 25. Imagine my surprise when I started shooting them and started seeing numbers above 3700 fps on my chronograph! Along with those numbers came blown primers and stuck cases. Same batch of primers, same cases, same canister of powder, same box of bullets, same seating depth. Outside temperatures were within 10 degrees on both days. Not a thing I can think of was different. After the third stuck casing I quit and went home, pulled the remaining bullets, and thought about it for a night.
Before starting over I mixed the canister of RL 25 thoroughly, checked my scale with the test weights, recalibrated it, rechecked it, and carefully measured out new charges, this time of 71 grains of RL 25.
I expected to see a reduction in pressure and speed. No such thing. More pressure, higher speed, more stuck cases. I went home early again.
Today I went back to the range with 69 grains of RL 25 loaded with the same primers, behind the same bullets, in the same cases, with similar weather. Almost four grains less than the loads that has yielded 3550 fps and no extreme pressure signs. After the first shot the chrono read 3785 fps, and before even trying the bolt I knew I was screwed...again.
SO WHAT GIVES? In working up loads I started at 71 grains of RL 25 and got speeds in the 3400 range and no pressure. I shot 71, 72, and 73 grains, no problems. Now I'm down to 69 grains and up to massive pressures...and speeds. If it were just pressure going up, OK, maybe a rough bore, but this is a custom Pac-Nor barrel with maybe 250 rounds through it, and it has been treated and cleaned very carefully. The only thing I can think of is that the batches of RL 25 were radically different, or that somehow the retardent is wearing off. Both of those theories seem really weak though, since certainly over seven or eight pourings into the powder measure the two batches would have mixed, and they shouldn't be THAT different to begin with. That is...unless the factory screwed up and mis-labled. Visually, I see no difference in the granules; they look like "normal" Rl 25 granules. Same shape, color and size. Also note that neither of the two cans of RL 25 I mixed was more than a year old, probably much less. I wish I had a fresh pound of RL 25 to try out, but you know how tight the powder supply is lately! I'm definitely NOT going to use ANY more of this canister, unless one of you can shed some light on this.
Frankly, I'm stumped. Ideas?