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Any consensus on what hollow base cavity shape is most likely to yield accuracy with mild pistol target loads or does it even matter? Looking around I see deep cones, elliptical, and hemispheric HB cavities. I know MP did at least one run of a HBWC that came with different pin shapes. I am aware that the pressure ceiling will be dictated by the thickness of the skirt (too high and they excessively deform or blow off). Might be up for some R&D.
Without any real science to back up what I'm about to say - I doubt it matters enough to be concerned about.
The purpose of the hollow base is to allow the skirt to be pushed into the rifling (sort of like a Minie' Ball expanding under pressure to fill the bore) AND to move the center of gravity forward (like the nose heavy shuttlecock used in Badminton).
It also allows for a longer bearing surface for the same amount of projectile weight within a given diameter.
My guess is a cavity with a hemispherical forward section and parallel walls would be more effective at letting the skirt deform to fit the bore and a cone shaped cavity would be stronger due to the thicker forward cross section BUT the differences in performance between those shapes would be minimal overall.
There might be a production advantage to a cone shaped cavity because the bullet would release from the pin during casting easier that one with parallel walls. I'm really just guessing here.
Without a doubt, the best shape is going to be what is easiest to get it to fill out and make good boolits.
That's sounds goofy simple but you know those .38 and .41 caliber hollow base wadcutter molds that Lyman used to make? My experience with both is that they're double extra yucky to try to get good boolits from. OK, so half the problem is having lube grooves like you was gonna be loading FFFg. And maybe they were actually made so large with the intent to take up space and give a really long barrel contact length but boy howdy are they ever a pain.
On the other hand I've got a hollow base wadcutter .45 mold (that I always loaded backwards:razz:) with small grooves and a hemisphere cavity that's a good casting mold.
Reckon if I was starting from scratch I'd want a scaled down version of Lee Precision's wadcutter minie ball with the corrugated exterior rather than lube grooves. But as to what geometry of cavity is best, not too small and not too large, and something that doesn't have flow impeded by an adjacent lube groove.
I don't think it will come into play until you get over 100 yards. I am not sure if that fits with your "mild pistol loads" or not.
Back in my revolver days it was well know that the hollow base wadcutters were more accurate. One benefit I attributed to a hollow base was the same weight bullet will be longer having more surface contact. Since a bullet is steered by its base any deformanity to the base will affect its accuracy, making me wonder why we don't have more nose pour bullet designs. On a standard cast bullet the sprue cut leaves a non-uniform base, so a pin system or any other to make a uniform base should be an asset.
The Lyman Ideal 358495 HBWC is a very accurate boolit for me in 38 special WC brass. I bought a NOE HBWC 2 cavity 38 Cal. mold that had a very different HB pin that was very hard to cast with. In shooting both boolits there was no difference in accuracy that I could detect. I modified the Noe HB pin to match the old Ideal pin so that the NOE mold would cast better. There was still no difference in accuracy that I could tell.
Here is a photo of the Ideal HB pin and mold...
https://i.imgur.com/Jq48GOJ.jpg
Photo of the base of the Ideal cast boolit on the left and the modified Noe boolit in the center and the original Noe boolit on the right.
https://i.imgur.com/VXWh0Sj.jpg
Don't know if any of this helps but I don't think the type of hollow base pin makes any difference in accuracy at the target. They do make a difference in how they cast at least for me..
I like your modification.
I don't have a problem with the NOE pins because I polished all of mine to a mirror finish as well as the tracks they run on. All my NOE molds are brass, so I run them hot, which makes a big difference on how well the pins fill out and drop. Additionally, I rub a coating of graphite on the pins and mold surfaces using the lead from a #2 pencil. The bullets just fall out of the mold. The graphite also inhibits the sticking of alloy to the block faces and top.
Dragonheart
It wasn't that my NOE pins were rough it was because they were to long and deep into the boolit that when the mold was opened the pins would rip the sides out of the boolit unless they were very cool.I tried all of your methods but the pins were to long. After I made new pins from the original pins the mold works perfect.
I can see how that would be a problem. I run two molds simultaneously so my bullets are firmly set when a mold is opened.
Original black powder .45 Colt rounds didn't have much of a hollow base in them, but soft alloy.
Modern Winchester lead .45 Colt factory rounds likewise.
Attachment 248808Attachment 248809
I really think bullet production will be the determining factor. The pin shape that allows for the easiest production of bullets will be the winner.
Thanks for all the replies, especially for all who uploaded pics. TCFAN, I appreciate your feedback on and modification of your NOE mold.
I found a few years-old group buy post that was buried in the back of my mind for a Mihec HB version of the H&G #50 (though this one as a HB drops significantly lighter than the prototypical 38 caliber HB wadcutter):
http://castboolits.gunloads.com/show...50-HBWC-38-357
This same design has also been run by Mihec as a standard base pour. It would be interesting to test (preferably from a Ransom rest) solids from a nose pour vs base pour from otherwise identical cherries.
Typically the rounded hb pins produce hb bullets that are stronger and can be driven full tilt/hot. Lyman made a lot of their hb pins with round ends, the trade off is the bases have to be perfect. Any imperfections and accuracy suffers. A nib lyman 358431 with the rounded hb pin.
[IMG]https://i.imgur.com/Adjeuw0.jpg[/IMG]
The cone shaped hb pins do not produce bullets that are as strong as the rounded pins. The short cone shaped pins like the ones in this cramer mold were designed to have a thick side wall and shallow cavity for strength. The bullets were intended to be used in the oversized 1917 45acp pistols. There isn't much difference between the rounded hb pin & short cone molds. Both have thick rims and small cavities, the cone design makes casting easier.
[IMG]https://i.imgur.com/tVkSHSw.jpg[/IMG]
The mihec hb pins in his hb molds (I have the 32/35/41/44/45 cal hb molds) are a long cone shape that produces a thin skirt and deep cavity. The thin skirt limits the pressures of the load but I have tested harder alloys and +/- 25,000psi loads with them. At the end of the day these types of hb bullets are best at what they are designed for, target work. The long hb cavity makes a long bodied bullet & as a longer expanded skirt that is grabbing/sealing/aligning/minimizing bullet defects.
[IMG]https://i.imgur.com/gWiB0IT.jpg[/IMG]
Raphine hb molds used a hb pin that is slightly conical. They produce bullets that have thick bases and deep conical shaped cavities. I have 35cal & 44cal hb raphine molds, they produce excellent bullets that not only perform well in standard sized 38 or 44 cal cylinders. They really shine in revolvers with over sized cylinders.
[IMG]https://i.imgur.com/cJlfXqH.jpg[/IMG]
Some 45cal cast hb bullets, there's round/conical/cone/long cone designs. The mihec top right & the cramer bottom left are the only 45cal hb molds I have left. Sold the other 2 a couple years ago.
[IMG]https://i.imgur.com/3f6cvSV.jpg[/IMG]
Making/using custom pins in the hb molds:
The fbi used to use a hb hp swaged lead bullet in their 38spl fbi load. Myself I prefer a 44spl & have carried/used the light weight ca bulldog since the 80's. Keith designed the 429422 hb bullet to be lighter/flatter shooting than his standard 429421 bullet. He used a round pin that produces an extremely strong bullet in the +/- 220gr range. I wanted a lighter bullet + a bullet that would seal better/faster producing higher velocities. In longer bbl'd firearms velocity doesn't matter much. In 2", 2 1/2" bbl.'s everything counts. After making/testing several hb pins I ended up with this pin for a 429422 mold.
[IMG]https://i.imgur.com/rVx5uvQ.jpg[/IMG]
Not really a good view of the bullets base. But the end result was a hb bullet that had a thick enough skirt that could withstand +/- 19,000psi loads with a 8bhn/9bhn alloy with a cavity deep enough (ends just short of the crimp groove) to seal the cylinders/bbl extremely fast increasing velocity. The hp was put in the hb bullet using a forster hp tool.
[IMG]https://i.imgur.com/FTFbMo6.jpg[/IMG]
A side view of the recovered/mushroomed bullet pictured above. The hb did it's job, there's extreme bullet body compression and the bullets base expanded along with the hp. That bullet was from a 1000fps+ load in a 2 1/2" bbl'd ca bulldog/44spl.
[IMG]https://i.imgur.com/Swqedh0.jpg[/IMG]
In 1900 lyman came out with the 35870 mold & I ended up with an older (no vent lines) hb version of that mold. Always thought it might make 1 heck of a target bullet for the 9mm. I tried several different hb pin designs & ended up with a hb pin that left a thick bullet base similar to the cramer 5f hb bullet. It had a conical shaped pin that ended at the bottom of the middle drive band.
[IMG]https://i.imgur.com/2nR3fks.jpg[/IMG]
That bullet did surprisingly well, 10-shot group @ 50yds fron a 1911.
[IMG]https://i.imgur.com/yRoLzs2.jpg[/IMG]
Never could get rid of the fliers, that 35870 bullet was just too long for the 9mm cases & the bases were getting distorted. I didn't want to re-throat the bbl and ended up selling the mold. The 35870 next to a mihec 125gr bullet. Both bullets had to be loaded to the same oal in order to past the plunk test in that bbl.
[IMG]https://i.imgur.com/V87WlTN.jpg[/IMG]
I used to swage a lot of hb bullets for the 32/35/44/45 cal's. Not so much anymore and sold most of the swaging dies off. I could make more, just don't see the need with 13 or 14 hb molds laying around. A couple of years back I was board & started playing around with junk I had laying around. The end result was with a bolt, washer & 2 pieces of scrap steel I made a swaging die to make .314" 32cal hbwc's out of cast lee 311-93-1r bullets.
[IMG]https://i.imgur.com/bG7YKsc.jpg[/IMG]
In the hb pin/shape/design world, 1 size/design is not a good thing. It's that jack of all trades, master of none thing.