Today's experiment was to try bullets with a long, slip-fit bore riding nose. The theory was that the long nose would guarantee that the bullet was aligned with the bore when the cartridge was chambered.
Rather than cut a new mold and pray that the nose dropped out exactly the right size, it was easier to make a nose die that would size the nose to exactly the right size.
Dimensions are from memory so they may not be exact but they're in the ballpark. The tapered section is approximately 2 degrees per side, the same taper as the leade.
Length A = 0.25"
Diameter A = 0.2455"
Length B = 0.1"
Diameter C = 0.2366"
We end up with a non-engraving glove fit. Contenders don't like to engrave or to jam the leade, so we have to settle for a slip-fit. With the bullets seated 0.007" away from jam, there was only about 0.1" of bullet inside the neck. In effect, this is the next best thing to a breech seated bullet.
The resulting 0.2365" nose does not engrave at all when chambered, but it does engrave hard if you try to stick it in the muzzle end. Apparently the bore is slightly bigger at the breech than at the muzzle. That is common and it's OK.
It should shoot like a house afire, right? Loads:
-- 21.5 gr. WC844
-- seated 0.007" away from contact
-- WW oven treated after sizing
-- HVR lube84 gr. bore rider, 10 shots at 100 yards:
-- 3.25" horizontal X 7.05" vertical
-- 2465 fps
-- 1.15% velocity standard deviation (mediocre, but better than usual for this powder)
-- two rounds popped the action open, suggesting that 0.007" away from contact was still too snug a fit for the Contender, bearing in mind that there will always be slight variations from one round to the next.
-- barrel was clean to the naked eye88 gr. lov-rider, 10 shots at 100 yards:
-- 4.3" horizontal X 10.35" vertical
-- 2485 fps for 2 shots, the chrono failed to see the other shots.
-- several rounds popped the action open, suggesting that 0.007" away from contact is still to snug for the Contender. I've usually had better luck with 0.015" away from contact, but wanted to try something different today.
-- barrel was clean to the naked eye, and a tight fitting patch did not show lead.Conclusions and Lessons Learned:
-- the long slip-fit noses failed to produce a major breakthrough
-- the long slip-fit noses did seem to reduce the horizontal dispersion.
-- for some reason vertical dispersion was the main problem (it doesn't help when the action pops open).
-- I do like using the nose die to produce perfect bore riding noses. It's more reliable and more versatile than depending on a mold to drop out the perfect nose diameter.
-- mostly I am still stumped as to why this barrel shoots so poorly at a measly 2500 fps? Things to Try Next Time:
-- at the end of the day I went ahead and shot five #280 grit firelapping rounds and five #500 grit firelapping rounds. The idea was to knock off any sharp corners or any machining burrs in the throat.
-- after the brief firelapping, the barrel had a mirror finish to the naked eye. The barrel had looked good before firelapping, now it looks great. I'm pretty sure the Shilen barrel is not at fault.
-- I'll retest some of my previous loads to see if firelapping produces a breakthrough. I've never had much luck with firelapping so I am not getting my hopes up.
-- I guess I could try a 0.246" bullet instead of 0.245". There's enough room in the neck. Based on my previous experiences with various rifles, I would not expect a 0.001" change in bullet diameter to make a big difference, but we can try it.
-- so far this barrels shoots light bullets as well as anything so the next bullet I make will be a light one, maybe 60 grains. It'll probably be a 1-diameter loverin and then I can always use the nose die to turn it into a bore rider.
-- mostly I am still stumped. I've shot a lot of imperfect barrels in my day -- sloppy chambers, rough bores -- and was usually able to coax a decent load out of them. So here we have a nice bore and a snug chamber and yet I can't get it to shoot decent, at least not at 2500 fps. It's a mystery.