Part 1
At the end of the trials described in Chapter 1, I had fired three loads of 5 rounds each, at 44, 45, and 46 grains of Lil'Gun behind the Hornady encapsulated 185-gr SWC bullet #45137. There were no observable or measurable signs of excessive pressure. Velocities showed a lot of variation around average velocity.
Because of that variation, there was little evidence that an increase in powder charge produced any significant increase in velocity.
I decided to increase the amount of powder to find whether such increase would produce higher velocities, or result in a decreased variability of velocity, or show any evidence of excessive pressure. I intended to halt the test of increasing charge should any signs of too-high pressure appear.
In this attempt, my first trial series started with a charge where the previous attempts had left off. I used the loading techniques outlined in the post of Chapter 1, Part 4 (15 June 09), except that here I loaded once-fired cases instead of new cases.
I used two cases for each load of 46, 47, 48, 49, and 50 grains of Lil'Gun.
I shot from a bench with the rifle clamped in a Lohman "gun vise"
http://southernhuntingsupplies.com/lohm ... unvise.htm
I put a sandbag of about 45 pounds on top of the barrel and action, and added another such sandbag behind the butt. The midpoint of the chronograph screens was set at nine feet from the muzzle. I pulled the trigger using a string, after I had stashed my tender torso behind a large tree about 20 feet away from the sandbagged gun. (Our club range is unused during much of the day, so I was worried only about spilling my own blood.)
Temperatures were a mild 76 F.
Ater the 10 shot series, the rifle had not disassembled itself. Here are the velocity readings (fps) from the chronograph:
Lil'Gun Trial 1 Trial 2
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46 gr - - - xxxx - - - xxxx
47 gr - - - 2858 - - - xxxx
48 gr - - - 2712 - - - 2879
49 gr - - - 2815 - - - 2750
50 gr - - - 2949 - - - 2900
(xxxx = no reading from the chronograph, or an obvious wacky reading.)
The cases had no measurable expansion at the head just in front of the extractor groove. The primers showed no evidence of flattening; there were no marks on the case head from the extractor. The bolt opened easily after each shot.
(Part 2, next post)