question about hollow base bullets

I wonder what the rifling twist rate was in that Zouave rifle ? Something I have noticed about the casting of the mini type bullets is that with the pointed hollow base pins it is very difficult to eliminate an air pocket in the bullet at the location of the point of the base pit. That pointed cone shaped pin seems to funnel and trap air at that point. Some bullets may even visually appear to be perfect but with a wee bit of pressure applied at this point with a dental probe most often an internal cavity can be detected.
On my Ideal mold I have modified the tip of the pin to be flat for maybe about 1/3" across. This simple mod has pretty much eliminated the issue resulting in much more consistently uniform bullets. One thing I was concerned with about the mod is how the bullet balance point may shift and affect the form stability of the original design. My gun is an early Euro-Arms 1853 model 3 band rifle musket with a 60" twist so the bullet form stabilized bullet design with the slow twist is a necessity. Fortunately the slight shift in bullet balance point seemingly had no detrimental effect on accuracy. The limiting factor on accuracy for me is the fairly crude sights that are terribly difficult for me to see clearly but even so I have managed more than one group hovering around 3" at 100 yards.
I asked the question starting this thread because I am undecided about my results. So far I am leaning toward filling the base and using a barrier between the bullet and powder. I acquired some 58 caliber (24 gauge) card wads from Track Of The Wolf and a load of 70gn volume FFFG black powder is shooting very well with this combination. Before acquiring the card wads I was using hornet nest paper as a barrier and it also worked well with the bullet base filled or empty but perhaps not quite as consistent as the card wad with base filled bullet.
I was just hoping to look at other folks loading technique for tips to maybe improve my own.

One great aspect of using the RB projectile is that they are the easiest to cast and since there are no grooves to catch between mold blocks and ball they almost always drop from the mold without effort. A 58 caliber makes a big enough hole and has enough weight to supply the momentum needed for penetration as proven by your incident.
My youngest girls are showing quite an interest in shooting ML rifles but the 58 is too much for them. We have just recently acquired an interesting antique but shootable 36 caliber. It is a target type arraignment but with very short pull length and fairly light weight, just about perfect for my young girls. We have not yet fired it but hope to soon. A rough check of bore diameter shows about a .365" groove diameter. I don't know the twist but plan to start with some light weight bullets about 125gn cast from a mold I use for 38.357 mag. I will cast them in pure lead and guess an as cast diameter of about .361" so loading even in a fouled bore should be easy. We shall see ! Girls are excited !

Understood but still with my experience in casting the un-modified HB mini and you know that is no small amount that I have to wonder how much of the accuracy problems were directly due to the bullets having the aforementioned internal voids.
I recently watched a you-tube video dealing with shooting these type bullets in these type guns and as he was waving the bullets he was bragging that he had cast himself in front of the camera and turning the bullet about in his fingers so we could see all angles I paying particularly close attention when he showed them with the base facing the camera I could clearly see a cavity at the precise location of the base pin point in the bullet. From a profile view the bullets looked good. This makes me wonder how many people are casting bad bullets but blaming bad results on the projectile type rather than the quality.
This will sound perhaps like I am ringing my own bell but there are very few people if any more experienced in bullet casting than myself. That said I could not consistently cast good quality hollow base bullets with the unmodified base pin in my Ideal mold #575213. With the modified base pin the bullets are a very consistent weight. With that understanding wouldn't you also question bullet quality as a possible source of trouble rather than putting the blame solely on the projectile type ?

That's just it, who looks ? What happened in my case is that I thought I had a large quantity of good bullets cast up when I noticed the void in one. Then going through the bullets found that about half of them had the visible void some grossly so. Then going through others that had no visible void or a very small visible void and testing them with a dental probe revealed the void hidden under a thin layer.
After modifying my base pin the void is virtually eliminated accept perhaps for the first few casts from the mold if it is not yet fully up to proper casting temp.
I watched a video of David Pedersolli testing some of their rifles using their molds and noticed that the hollow bases of the bullets made from their molds have a flat not pointed cavity just as I have modified mine to have. There seems to be a quirk involved with what is happening inside the mold with the pointed base pin. Somehow it is capturing air in the splash and funneling it to the point of the pin and being trapped there in the bullet. This too I believe is also compounded when casting pure lead that has a faster freeze time than harder lead alloys containing tin and or antimony. These alloys at the same temperature will take slightly longer to freeze ( maybe not the best descriptive word) and so allow more time for the air to vent out. I guess I should say these are my observations based on my experience but perhaps not necessarily gospel.
What I can say for sure is that I will no longer even try to cast pure lead hollow base bullets with a pointed base pin.

OH and BTW Joy and I tried that 36 today and it seems a fine shooter. It was getting late and cold but we were anxious. I cast some pure lead 125gn 357 bullets as well as some from a 36 cal maxi mold I had on hand. The 36 maxi miced right at .360" diameter which is what I always size bullets to for the 357 mag and 38 special.
The as cast pure lead 125gn bullets shot great on 20gn of FFG which is what we had handy. The 36 maxi shot well too. This was also a good chance to test our new Black Ice winter black powder lube and it worked well indeed. We didn't try for any formal grouping but found it quite easy to keep shots on the 4" bull at 100 yards. Now as promised on my next day off it and a 45 cal Lyman will accompany myself Joy and Arahlee on a hunt for some cottontails that they do so enjoy.

Daniel, reading your post about finding air pockets in .577 Mini Ball castings, brings back memories of the 1960's & early 1970's, prior to Oct. 1973, when I got married, & inherited 2 young daughters in the process. As I moved 165 miles away from the family farm, to a small home on a lot, I had no place to shoot, so my bullet casting, reloading, & just going out in a big field, popping caps, burning powder & sowing lead in the fields ended until the winter of 2015, when I started learning about Black Powder Cartridge Shooting & reloading for my .45-70 & .50-70 rifles. I wasn't very scientific about my casting bullets from my SAECO melting furnace, but got a lot of bullets in .52, .577 (.58) .44 W.C.F., .44 Spl/Mag. .45 Colt, .44 RB, .45 RB.  I too noticed the imperfect area at the top of the cavity. I played with the melt heat, up or down a few degrees, dropping them onto a dry towel, & dropping them into a bucket of cold water. It didn't matter, most still had the air pocket. My moulds are all Lyman, so they are decent moulds. One time after moving here, I went to an auction that had a Trapdoor .45-70, a Springfield .58 Musket, & other related items that had belonged to the seller's grandfather, who had spent several years of his life in the U.S. Army during the Civil War, & later on duty in the West. When, after it was too late tobid on some items, while talking with the retired judge, I asked why his sons & grandsons didn't keep these things, he told me that they weren't interested in family heirlooms. But to get back to the subject, I bought a large wooden box with many already loaded .58 cal. rounds in round cardboard tubes, "ready to load". The Judge had belonged to a North-South Skirmish unit, & they did demonstrations on holidays such as 4th of July & etc. As I have donated my .58 Colt 1861 "Special" rifle to the American Legion War Vet Museum, in Canfield, Ohio, 11 miles from where I grew up, I have no use for those bullets. So last summer, I de-miled them, by pilling the bullets from the tubes, salvaging very close to 1 lb. of 2F BP. These bullets were lubed (dry by then) in the grooves, but nothing in the hollow base cavity. I was going to melt them into ingots, but decided to wait & see if anyone might want to buy them, to save time from casting. Tomorrow, after we get back from my M.in L.'s 94 th BD dinner, I'll get some of those bullets out & examine the cavity in them.  I'll let you know what I find.

Look at the bullets in this video. These are from the Pedersoli mold as well as a modified Lyman 575213. My modification to the Lyman 575213 is much the same as this.

The fellow in the first video also makes his own powder so is apparently quite involved in making ML's shoot. He has several videos on extreme long range shooting with traditional ML.