Whitesheep - after settling on an optimum powder charge (determined with all bullets seated .050" off the lands) I essentially did another ladder test with the only variable being the seating depth. The bullet-to-lands range I chose was .025" to .060" (Barnes recommends .050" as a starting point) in .005" increments, with six shots per increment. The bullets were color coded, by seating depth, with a Sharpie after loading and then mixed in random order for the test. The test was "blind" in the sense that I was unaware of each bullet's seating depth as the test proceeded.
Range procedure:
Tested at 300 yards using Lead Sled
Fired three foulers, then fired 16 test loads (target #1).
Cleaned barrel
Fired three foulers, then fired 16 test loads (target #2).
Cleaned barrel
Fired three foulers, then fired remaining 16 test loads (target #3).
I did this on a cool, calm day and took my time to minimize barrel heat-up.
I brought the targets home, touched the bullet holes with an alcohol-soaked Q-tip, and the paper lit up with the colors. I then measured and recorded x, y, and total distances from the origin (bulls-eye) for each hole, threw out one (worst) flyer from each set of six, determined the average dx and dy for each remaining set of five, and determined the SD for each set of five relative to average dx and dy. I also determined the total distance from hole #1, to #2, #3, #4, #5, then #2, to #3, #4, #5, then #3, to #4, #5, then #4 to #5, then the average and standard deviation for each set of ten measurements for each set of five. Theoretically it would have been better to have a larger sample size but I decided on a 48 shot limit, not including the foulers. Statisticians would probably fuss at me but enough is enough. The math part probably sounds like a lot of work but it's not bad if you're handy with Excel.
The total distance (hole-to-hole) Standard Deviations for each set of five were as follows:
.060 - 1.42"
.055 - 4.08"
.050 - 1.66"
.045 - 0.79"
.040 - 1.24"
.035 - 1.43"
.030 - 1.34"
.025 - 1.80"
.045's dy (vertical) results were the best by far (SD = 0.28" to second best 1.16") and dx (horizontal) results were second best (SD = 1.08" to best 0.70").
So you can see that .045 clearly gave me the tightest five-shot group. .040 was second best, supporting the indication of a sweet spot. I also plotted the hole coordinates on separate graphs and it was plain as day.
Might .044 or .046 be better? Maybe, but the .045 results are good enough for me.
Ideal barrel to frame gap? The idea is to minimize the movement of the round during the firing process while avoiding head contact with the frame prior to firing - in other words, ~.001" head space. I think a .002" barrel-to-frame gap is very good in a mass-produced modular rifle like the Encore (head sticking out of barrel .001" results in .001" headspace). Greater gaps can be dealt with relatively simply by tweaking the shoulder to head dimension (within reasonable limits) if you're a reloader and/or by using headspace shims. Some argue that this whole issue is overblown with respect to Encore accuracy but as you can probably tell by now, I'm a stickler for detail, so I definitely consider it in my own reloading.
You can find more interesting reading on the headspace subject at Mike Bellm's website (if you haven't already found it).
Hope this helps,
MA
