Today's goal was to try to shrink the horrible velocity variation, which is due in part to resistance when chambering.
I made a nose die to size most of the bullet down to 0.358" for an easier fit in the freebore while maintaining a 0.359" base for a good gas seal. Or at least that was the theory anyway.
Here's how it turned out when seated just off jam.
The 0.358" x 0.359" bullet did chamber easier than last weeks 0.359" bullet, but there was still a bit of drag and there was still no definite "jam" point.
I measured the jam from breach to base for several 1-diameter 0.359" bullets, pushing with 3 pounds of force:
-- 1.060", 1.064, 1.003, 1.063, 1.018, 1.057, 1.029, 1.039. Average= 1.042".
Then I measured the jam for several 0.358" x 0.359" bullets, again pushing with 3 pounds of force:
-- 1.222", 1.218, 1.225, 1.213, 1.232, 1.225, 1.203, 1.216, 1.209, 1.191, 1.208, 1.221. Average= 1.215".
The bullet was 0.775" OAL, so adding that to the 1.215" jam yields 1.99 COL to just barely reach the jam point.
For starters, we repeated last week's charge of Lil Gun to see if the nose-sized bullet was an improvement.
-- 17 gr. Lil Gun
-- Winchester mag primer
-- 1.973" COL (0.017" away from jam)
-- 1997 fps vs. 2021 fps last time
-- 1.55% velocity standard deviation vs. 2.42% last time
-- ES=3.53" vs. 3.12" last time
-- MR=1.08" vs. 0.88" last time
Conclusion: the nose-sized bullet chambered easier and the velocity variation was less horrible, otherwise no improvement.
Reduce the velocity and seat a bit deeper for less chambering resistance
-- 16.6 Lil Gun
-- 1.963" COL (0.027" away from jam)
-- 1947 fps
-- 1.76% velocity standard deviation
Conclusion: no improvement in accuracy and it still leaded.
Switch to WC297, which usually leads less:
-- 18.0 WC297
-- Win mag primer
-- 1962 fps
-- 2.48% velocity standard deviation
Conclusion: perhaps slightly better accuracy and slightly less leading, but the velocity variation was still awful.
Today's target. Note that the horizontal dispersion was 1 1/4" - 2 1/8", which is decent. But the lousy velocity variation is causing vertical fliers -- fast shots land high, slow shots land low. So the #1 priority is getting the velocity variation under control.
Leading is always subjective. What looks dirty to one person may look OK to another person. I find that even when using a bore scope leading is still a judgement call. My gold standard for judging leading is simply to push a tight fitting patch through. If there is "hard" leading, you'll probably see slivers of lead on the patch, and there will still be visible leading in the bore. But if there was only "soft" leading, there should be no slivers of lead on the patch, and the patch alone will probably leave the bore clean. All of today's loads flunked the patch test, though WC297 seemed less guilty than Lil Gun.
To add to today's fun, one of the Eagle Arms bolts broke. I swapped in the bolts from my 6x45 barrel and continued shooting, though while swapping bolts I noticed that the Bellm bolt spring seemed to have taken a set. In fact, the action popped open 3 times today, for the first time since I installed the Bellm spring.
At the end of the day I examined the bolt spring more closely. Yep, it has taken a set. In fairness to the Bellm spring, I'm not sure that the Eagle Arms stub compresses the spring as much as a TC barrel? In any event for now I solved the problem by cutting 3 coils off an old spring and inserting those 3 coils in before the Bellm spring.
Continued in the next post .....