Part 1
(NOTE: My reports here are based on my bolt rifle. Do not expect similar results from any other rifle. Remember, you're finding this information on the internet, where 10-year-olds can describe how they shoot 2-inch 20-shot groups at 800 yards with terminal velocities above 3900 fps.)
The trials described in Chapters 1-3 with 185-grain SWC bullets using Lil'Gun and 296 led me to conclude that these were not ideal powders when loaded with conventional methods. I was able to get muzzle velocities up to about 2900 fps, but with unacceptable variation in velocities. Apparently initial pressures are not high enough to cause an efficient burn of those powders behind the light bullets.
Those trials did show that worry about the possible in-flight disintegration of light-weight bullets in my 1:16 twist barrel was negligible. Accuracy is not yet a concern.
Possible alternatives seemed likely to allow higher velocities: (1) Some mechanical modification that will help initial ignition of the powder, for example crimping. (2) A hotter primer, for example using a sawed-off 284 case with a LR primer, with which BD1 has been working. (3) A faster burning powder.
I decided to try option #3 first.
From a QuickLoad simulation for 200-grain bullets posted 7-18-08 on the calguns thread, a possible candidate in the powder locker was Blue Dot. Wildcatter mentioned somewhere that he'd tried Blue Dot, so I wasn't going into totally unexplored terrritory, except possibly with the use of the 185-grain bullets.
I loaded up a series of one cartridge each of 21, 22, 23, 24, and 25 grains under the 185-grain encapsulated Hornady SWC. (The sample size is small, but this was an initial what-if type of exploration.) Cases were 1x fired. The COAL to 2.000. Primers were CCI BR4.
Because I had no idea of what to expect, I sandbagged the rifle and fired it with a 20-foot string, as described in Chapter 2. As you might expect from the light charges, the rifle stayed together, and no signs of excessive pressure were observed. Sooting on the cases and zero case expansion in front of the extractor groove both indicated pressures were relatively low. Chronograph readings at 9 feet were:
21 grains . . 1549 fps
22 grains . . 1644
23 grains . . no reading (dead chrono battery)
24 grains . . 1796
25 grains . . 1868
The steady increase in velocity with increasing charge was encouraging.