Yesterday I tested several things: 1) Ardito style sizing and loading 2) I wanted to give Lil Gun another chance because Quickload thought it could safely gain 50 fps over WW296 / H110 3) firelapping the Green Mountain barrel and 4) the Mike Bellm bolt spring.
Firelapping consisted of 10 rounds of 280 grit followed by 10 rounds 500 grit. To the naked eye, it left a mirror finish. However, with the bore scope I could still see some roughness. There was also a surprising amount of pitting -- I have no idea what caused the pitting? It's not deep but it's there.
A bullet sized in the nose die, and loaded so that it was 0.012" away from contact.
Quickload thought that Lil Gun could push the 160 grainer to 2025 fps while WW296 / H110 / WC297 could only go 1950 fps. However, Quickload is not always right. In reality both powders maxed out at 2000 fps. At 2050 fps cases would begin to stick so that was the practical limit, and I backed down to 2000 fps to ensure reliable functioning.
The good news is that before firelapping I was running into leading above 1950 fps, after firelapping there was only minor leading at 2000 fps and the leading did not get any worse as more shots were fired. When I say "minor" I mean it looked great to the naked eye and the bore scope revealed only a few spots with tiny specs of lead, mostly in the corners of the grooves.
However, neither the firelapping nor the Ardito-style loading seemed to improve accuracy. Starting out with Lil Gun
-- 15.3 gr. Lil Gun,
-- 1.866" COL (0.012" away from contact)
-- 1967 fps
-- 1.48% velocity standard deviation (poor)
-- 11 shots in 2.75" at 100 yardsSame as above except increase the charge of Lil Gun
-- 15.5 gr. Lil Gun
-- 1987 fps
-- 1.01 % velocity standard deviation
-- 11 shots in 2.75"Increase charge of Lil Gun and nose-size bullet deeper and seat out farther
-- 15.7 gr. Lil Gun
-- 1.916" COL (0.012" away from contact)
-- 2007 fps
-- 0.99% velocity standard deviation
-- 11 shots in 1.9"
-- 11 shots in 2.6"Same as above except switch to WC297
-- 17.0 gr. WC297
-- 2000 fps
-- 1.71 % velocity standard deviation
-- 11 shots in 3 1/4" but 8 shots in 0.9"
-- one of the fliers was the fouling shot, the other two were unusually high velocity (2057 fps and 2051 fps). Conclusions and Lessons Learned
-- firelapping made the barrel look better and foul less, however there was no improvement in accuracy.
-- firelapping allowed the velocity to be increased from 1950 fps to 2000 fps.
-- no obvious improvement in accuracy with Ardito-style sizing and loading, compared to a 1-diameter bullet.
-- WC297 acted like it wanted to shoot one ragged hole with the Ardito bullet, but lousy velocity variation caused vertical fliers.
-- I'm still puzzled why this barrel shot more accurately with it's original "bad" chamber than with this current chamber which seems to be a very good chamber and throat?
-- there were no pop-opens with the Mike Bellm bolt spring, not even when I unintentionally ran the velocity up to 2200 fps and had to tap the cases out of the chamber with a cleaning rod.
It takes two hands to open the action with the Bellm spring -- I can do it with one hand if I try hard enough but it's very difficult.
-- as I am also learning with the Contender 6x45, high velocity cast loads want to engrave the rifling but that just doesn't work in a Contender. For reliable chambering you have to jump to the rifling and that limits accuracy and makes it tough to ignite slow powders, hence the perpetually lousy velocity standard deviation.
-- unless some breakthrough comes along it looks like the best this chamber will do with high velocity cast is 2 MOA
(vs. 1.6 - 1.8 MOA with the original "bad" chamber).Things To Try Next Time and Down The Road
-- a few more firelapping shots. The bore scope reveals that there is still a little roughness and fouling in the corners of the grooves.
-- I could try tweaking the jump-to-rifling on the WC297 load, though my previous experience suggests that I'll never get rid of the velocity variation.
-- do a side by side comparison of 1-diameter vs. Ardito style.
-- down the road I may recut the leade to 1 degree instead of 1.5 degree, but I'm cautious after the failure with the 1/2 degree throat. In theory there is nothing wrong with a 1.5 degree leade.
-- down the road I may try some minor tweaks to the 160 grain spitzer, like changing the GtoB to 0.8 and making the nose longer or shorter.