Cavities in cast bullets - if you can't see it don't shoot it

[Pat in Virginia]

The following is an excerpt from a recent post by Bill Curtis, a man who knows what he is about with these sort of things. I think you will find it most interesting. The subject came up in the context of a 2-band Parker Hale rifle.

If you are familiar with the Curtis & Harvey brand of powder of old, Bill is of that family:

In the days when my eyes worked properly, that rifle regularly scored ninety plus on the PL7 at 100 metres, best ten of thirteen rules. That was with the 200 sight setting. It had the happy knack of usually putting the first sighter into the ten ring. As the shoot went on it started to wander a little but I put that down to fatigue. The important thing is that I could trust that load which never varied.

As I rarely shoot these days due to age, I will let you into a little secret.
In my experience all cast bullets have cavities which may or may not be seen. Take a number of bullets with no visible cavities and cut them in half longitudinally. Most will have concealed cavities which will be in different places. My system is to accept that cavities are unavoidable so I cast in such a manner that the sprue is minimal size which allows the setting lead to suck air down into the pouring hole. The result is a visible cavity which most people reject. I use none but these because I know where the cavity is, it is always the same size and it is where I want it to be, in the nose. Probing with a pin shows the depth which does not vary. The bullet weights are also checked and are remarkably consistant, outside +\- one grain they leave the batch. Also I use only the purest lead I can get. I do not know anyone else who uses this system but it got me results plus many comments about using visibly defective bullets. He who laughs last laughs loudest (to purloin a phrase).
W. S. Curtis, A.C.I.I.,
Vice President (Hon.), Crimean War Research Society,
HBSA (Hon. Life),
Assistant Curator, Museum of the National Rifle Association,
Whitworth Rifle Research Project,
MLAGB, NLRC, ATRA, &c.


The reasoning behind the notion that all cast bullets have cavities, seen or not, is that the bullet hardens on the outside first and stops shrinking while the inside is still molten. When the inside finishes shrinking it leaves a cavity as it does not collapse the outside of the bullet that having hardened already. If you can see it, it's a cavity; if you can't it's a hidden vacuum not an air bubble; in either case it's there (or, so they say).

The idea that all cast bullets have cavities is not new. You can find it in some shooting publications of the 1860s. It's one of the primary reasons the Brits used swaged bullets in their ammunition.

I did find it novel that Bill only shoots those bullets, .58 Minnie's, that have cavaties he can see and discards the ones where the cavity is not visible.


Hmmm!

:)


Pat in Virginia

[Lou Lou Lou]

Instead of culling out the ones with base cavities, I will save them and see if they group.

[Ron/The Old Reb]

I always reject the ones with base cavities. But have shot them to see if it makes a difference and they seem to shoot the same.

[tony 1st regt]

I do a visual inspection and also weigh bullets. The ones that have a defect in the base cavity I use to shoot team competition, the ones that seem perfect I use for individuals. Bench testing shows a very small difference in accuracy for the distances we shoot, but in individuals I need all the help I can get so I use the good ones.

[Jim Leinicke 7368V]

I am familiar with Bill Curtiss, and his form of shooting is long-range, prone shooting of Long Enfields for maximum accuracy. He and his fellow target shooters over there go through all sorts of elaborate proceedures to get absolute consistency, even going so far as to handle a powder flask the same way with every loading to assure no sifting of grains of powder, etc. etc. This type of shooting is worlds apart from what we do (Close range, off-hand). His point on the air cavities is probably valid given the type of target shooting done in the UK, but for those of us skirmishing it is for all practical purposes irrelevant in my opinion.

Jim Leinicke
7368V

[Pat in Virginia]

Jim,

Would you say then that if the bullets all weigh within a couple of grains, cavity or no cavity being visible, just shoot them and don't worry about the ones with the visible cavities?

I think a lot of folks do reject, perhaps needlessly, the bullets with visible cavities.

By the way, if the bullets do weigh about the same then it's reasonable to assume that the ones with no cavities being visible must also have them. I'll have to check that out the next time I'm casting Minnie balls. Come to think of it, I'll have to look through some that I cast in the past and see what I find.


Pat

[Jim Leinicke 7368V]

Actually, I think our British friend Bill Curtiss is probably correct from his perspective. If you are REALLY going for top consistency for long-range, supper-accurate shooting, keep the ones with a uniformly centered and visible cavity and reject the ones that look good! However.... What I am saying is that with the ranges at which we shoot, and given the fact that we are all out there on our hind legs waving barrels around to a greater or lesser degree (H.P. Gregory the lesser, J. R. Leinicke the greater), that grain or two variation, or that hidden bubble a bit off-center, ain't gonna make a cat's whisker difference.

Personally, I am real critical about having nice, sharply uniformed bases, particularly the skirt area of a minie, where a bit of a flaw might cause a rupture and a wild shot. Seems plenty good for the likes of me. I have tried the weighing and sorting nonsense, found it made absolutely no difference, and decided I have lots of other more rewarding ways of wasting my time. Incidentally, I always found the greatest variations in weight to be found in the bullets that had no visible base cavity.

Jim Leinicke
7368V

[Maillemaker]

Seems to me the best way to deal with all of these issues is to use swaged bullets.

I'm surprised it is not more common.

Steve

[Pat in Virginia]

I did find a batch of bullets where I had eliminated the ones with base defects and other obvious flaws, but not those with base cavities.

Examing 510 gr (approx.) Minie bullets from an earlier casting session was interesting. I had some bullets that I had made a first pass on and eliminated any with obvious base defects, wrinkles, etc. I found I did have some with small cavities visible. They revealed themselves generally by having a pin hole at the top of the cavity. I inserted a thin wire in the hole and found that the cavity went a bit deeper, but they were not large cavities.

I sorted out 13 Minie bullets with no obvious cavities and 11 with visible small cavities. I then weighed each of the two sets (those with and those without cavities) and eliminated the outliers from each group as I would normally using +/- 1 grain as a rule of thumb for non-aperture sighted rifles. See the table below (unfortunately I had trouble formating it - the forum editor removes the extra blank spaces hence the "."s

NOTE: Underlined bullets (weights) were discarded due to too much weight variance for their group

No Cavities Visible.....Visible Cavities
01- 507.9 507.9 507.9.... 507.6 507.6 507.6
02 -508.7 508.7 508.7 ....506.1 506.1 507.3
03 -511.1 507.8 507.8 ....509.2 507.3 507.7
04 -507.8 506.3 507.9 ....507.3 507.7 508.2
05 -506.3 507.9 508.2 ....507.7 508.2 506.9
06 -507.9 508.2 507.9 ....508.2 506.9 507.7
07 -508.2 507.9 508.1 ....506.9 507.7 507.2
08 -507.9 508.1 508.9 ....507.7 507.2 508
09 -508.1 508.9 508.2 ....507.2 508 ...507.6
10 -505.4 508.2 508 .......507.6
11 -508.9 507.6
12 -508.2
13 -509.2
Avg weight:......508.18... ...................507.58

Concerning my observations from this sample of bullets shown in the table above let me make it clear that this is not a valid statistical study as the sample size is far too small. What I did find interesting from this experiment was:

1. Once the outliers were eliminated, the variance in weight between cavities and no cavities visible was not that much, roughly ½ grain when comparing the averages.

2. One of the bullets eliminated from the Visible Cavity (VC) group weighed 509.2 grains which was heavier than all but two of the bullets with No Cavities Visible (NCV). Also, the bullet with the least measured weight was found in the NCV group.

3. Using only weight as a guide, all of the final VC bullets but one would have met the +/- 1 grain requirement of the NVC bullet group.
Finally, a general observation: the reason for rifling is to make variances in the weight distribution in the bullet of far less significance to its path of flight due to the spin, gyroscopic effect, imparted by the rifling. So maybe we can ignore at least small cavities in our bullets and not discard them if they otherwise appear to be fine.



Pat

[Pat in Virginia]

But first, Jim I think we are on the same wavelength per your last message.

When casting a lot of bullets, I will place the cast bullets remaining after the visual inspection vertically on a flat board with a marker tape that has bullet weight marked in ½ grain increments according to their weights such that I get columns of bullets that all measure to the closest 1/2 grain. As I shoot at different ranges, mainly 100 yards and 200 yards, and use rifles with aperture sights often I don’t mind having several groups of bullets that are +/- 1 grain in weight in groups of 20. I require that the bullets be well filled out with no base defect or other obvious defects. If I am casting .451 500-575 grain conical bullets I don’t even mind if the base is a little rounded at the edge as I will be putting a card wad under it, maybe even a wad stack (hard card-felt-hard card). I put .451 bullets in MTM .45 auto cartridge boxes in order of least to most weigth in a particular group of 20. I mark the boxes by the range of weight they contain.

By the way, if memory serves me correctly Capt. Heaton, a top British ML shot of the late 1850's and early 60's said that a variance of 4 grains in a 500 grain (or so) bullet made very little difference on the target where as small variations in powder weight were far more problematic, especially at longer ranges.

A final thought, as our moulds do not stay at the same level of heat due to distractions, cooling between bullets, etc. and because the heat of the melt is varying constantly we have to expect/tolerate some degree of bullet weight variance. What is acceptable is determined by the truth the target of interest tells at the range of interest.



Pat

[Pat in Virginia]

Steve,

I would love to use swaged bullets if I could do it for a reasonable cost in equipment.

For example using a RCBS (Rock Chucker Bullet Swage) Rock-Chucker bullet press. Then there are the dies, etc.



Pat

[Maillemaker]

Tonight I took some of my cast bullets (RCBS 500M) and sliced them in half with my bandsaw.

The bandsaw smeared the lead considerably, as you can see, which might have masked any voids, but there was nothing obvious that showed up.

http://i.imgur.com/zBgBF.jpg

Steve

[Southron Sr.]

I have a casting machine and as I make up bullets for myself and some of my family members, I generally run about 1,000 bullets at a time.

First and foremost, I trot down to the local hardware store before every casting session and pick up one of those spools of 50/50 solder. 50/50 solder is half pure lead and half pure TIN. DO NOT GET THE SOLDER WITH ROSIN IN IT.

Always throw some of the solder in every pot of lead as even a tiny bit of TIN will make your bullets pour easier and fill up the mould better and there fore REDUCE CAVITIES.

I think it was Pope the legendary barrel maker that proved that IF a bullet has a good base, it will shoot fairly accurately EVEN IF THE NOSE IS A BIT MESSED UP. This explains why some shooters that pound their Minie Balls down with the ramrod and deform the nose of their bullets can get fairly good accuracy.

I visually inspect my Minie Balls and discard ALL with any visible cavities. They get melted down again.

Then I weigh ALL of my Minie Balls on an electronic scale. What I find is that the weight of my cast Minie Balls fall into a "Classic Bell Shaped Curve."

All of my light bullets get melted down, the theory that they have a hidden cavity somewhere in them.

All the ones that are within "Plus or Minus" two grains become my "Match Ammo." Everything else is "Practice Ammo."

What I know from experience is that [1] I CAST WITH HOT LEAD AND A HOT MOULD (BUT NOT HOT ENOUGH TO CAUSE "FROSTED" BULLETS.) [2] BIT OF TIN in each pot of lead will dramatically reduce the cavities in your bullets and make your lead cast much easier. Your bullets will also come out a tad "Brighter" because of the Tin content.

Those two "Secrets" will dramatically increase the quality of your cast bullets and reduce cavities to a minimum

[Maillemaker]

Last weekend I had one of my worst casting sessions ever, in terms of visible voids. I cast 222 bullets, and roughly half had obvious voids at the point of the hollow cavity.

Based on this thread, I decided to do some measurements. I weighed all 222 bullets on a digital scale. I split the bullets into two groups: those with a visible void, and those with no visible void.

There were 120 bullets with no visible void. The average weight was 538.16 grains.

There were 102 bullets with a visible void. The average weight was 538.37 grains.

This is a difference of only .21 grains.

What this tells me is that the observations of others in this thread seem consistent. It would appear that there is little difference in mass between bullets with visible voids and those without, which means, as others have suggested, that even perfect looking bullets probably also have internal voids.

Now the question is, where are those hidden voids?

I think there may be some merit to choosing visible voids over invisible ones. With visible ones, at least you can know where that void is, and thus the center of gravity of the bullet is consistent. But if that void is somewhere else in the head of the bullet, the center of gravity may be moving rearward.

Steve

[Maillemaker]

I happened to stumble upon this video where a guy takes high-speed video of .22LR bullets that have been purposefully off-balanced:

http://www.youtube.com/watch?v=C9Dylxy3zJc

Notice the marked inaccuracy.

What I have done to "eliminate" voids in my minnie balls is to cant the mold at a 30-40 degree angle. This seems to eliminate the void at the top of the core pin for the hollow base.

But what if all this is doing is shifting the void off-center inside the head of the bullet? This would unbalance the bullet.

My mass measurements above seem to indicate that the void is there, visible or not.

Maybe the best thing to do is a straight-in pour and live with the void after all?

Is there something about the shape of the core pin itself that causes the void? I wonder if a more blunt tip would help?

Steve

[medic302]

pat in virginia posted about swaging minis. i swage LRML bullets, i've read every technical manual produced by david and richard corbin. here is exactly how to swage a minie. if you intend to swage a pritchett type ball which is paper patched the process requires one less step than a grease groove bullet which given the rules of the NSSA most people would swage gg bullets. first off you need the press, the RCBS rockchucker swage press will not swage bullets bigger than small pistol bullets. the reason is it will fall apart, the linkages aren't designed to have that much force applied, and the press isn't big enough to create the necessary force. so, you need to get a real swaging press from either richard or david corbin, richard is the cheaper of the two but doesn't do experimental work but will still make pretty much any standard form of bullet you could dream of. David on the other hand with make anything under the sun but is far more expensive and slower. that being said, both corbin's do exceptional work and are extremely knowledgable and nice. my press is richards Walnut hill press, it cost around 550$

next you need dies, you have some options here, the cheapest and fastest way to make any paper patched bullet be it minie or otherwise is to make a SWC style. with this die set, the core, nose and base of the bullet and the excess lead is extruded in one stroke. you can get any style nose or base shape you want, it will just be a SWC. the other option for dies is the two die set which makes a bullet with a smooth ogive, it has one die for core swaging and the second is the point forming die. the core swage die takes the billet of lead wire and swages it into a uniform cylinder of lead .001" under the finished dia. and +/- .5grn of the target weight, every time. once you have the cores swaged, you run them through the point forming die, this puts the nose and base on the bullet, brings it up to the finished dia. either way makes great bullets without 800 degree lead and the hazards that come with casting. i think i paid around 400$ for my two die set.

if you are paper patching your bullets, the process stops here. for grease groove bullets there is one extra step, you have to cut the grease grooves into the bullet. this is done with corbins grease groove cutting tool. i paper patch, so i have not used it, i do have a friend who does and he swears by it so there you go, that's how you would swage a minie. the hardest part is knowing what bullet shape and dia you want, the bullet length and weight can be anything you want because you control that on the press. i.e. you can make any weight bullet with the same shape and dia on one set of dies, where as a mold would have to be either adjustable or completely differant molds.

hope this helps you guys out a little.

[Pat in Virginia]

Tanks, Medic, ;) your post was very informative.

Pat in Virginia


PS - Would your observation regarding using an RCBS Rock Chucker press apply to .451 bullets (in your opinion): 1) for soft lead; 2) for 20:1 lead?

I realize I may be taking you out of your realm of comfort and if so, just say so. It's been suggested to me that for a .451 bore (bullets reduced in diameter for PP) an RCBS press will work for 530 grain swaged PP bullets even with a 20:1 alloy. This by someone who shoots very successfully at the 1000 yard level. He hasn't been swaging bullets very long with the RCBS press so time may tell on his RCBS RC press.

[Maillemaker]

I think it would be fun to make authentic Enfield-style bullets that use the Prichett style of bullet, which would lend itself extremely well to swaging, but unfortunately I do not think paper patched bullets of any sort are legal for N-SSA competition.

I have read Corbin's web site and the usual method for making bullets with grease grooves is to use their grooving tool which does not cut grooves but rather makes them by displacing material. The good news is this does not change the mass of the bullet, the bad news is it means you have to size your bullets after making the grease grooves. Also you are limited to rather shallow grooves.

The proper way to do it would be with a 3-piece die, as I understand they were done in period.

Steve

[medic302]

Tanks, Medic, ;) your post was very informative.

Pat in Virginia


PS - Would your observation regarding using an RCBS Rock Chucker press apply to .451 bullets (in your opinion): 1) for soft lead; 2) for 20:1 lead?

I realize I may be taking you out of your realm of comfort and if so, just say so. It's been suggested to me that for a .451 bore (bullets reduced in diameter for PP) an RCBS press will work for 530 grain swaged PP bullets even with a 20:1 alloy. This by someone who shoots very successfully at the 1000 yard level. He hasn't been swaging bullets very long with the RCBS press so time may tell on his RCBS RC press.

hi pat, i'll give you what i know from reading the technical manuals. the rock chucker is a good press but the problem with all reloading presses in regards to swaging, is the linkages aren't built for long term use with big bullets. it can do it for the LRML bullets but the question posed in the technical manuals is for how long? another issue to consider is in regards to pritchet bullets, being a larger dia, can the RC produce enough force to still swage the lead? the swaging presses are built heavy enough and with enough leverage to produce enough pressure and never fail mechanically.

in my opinion, if i was going to use a RC press to swage LRML bullets i would use soft lead, probably no more than 40-1, once again though, for how long? for the 20-1 alloy bullets, which can be swaged btw, the die maker needs to know what alloy you will be using, the harder the alloy, the larger the bleed hole needs to be or you risk cracking the die. that being said, a die for a hard alloy cannot be used with soft alloys. (the bleed hole will be too large to generate enough pressure inside the die).

another option for inexpensive swaging, would be to use a pound die. for those that don't know what one is, its a die that you strike with a hammer to make the bullet. it's a simple set up, but slower bullet production. it is also popular with some LRML shooters.

[medic302]

I think it would be fun to make authentic Enfield-style bullets that use the Prichett style of bullet, which would lend itself extremely well to swaging, but unfortunately I do not think paper patched bullets of any sort are legal for N-SSA competition.

I have read Corbin's web site and the usual method for making bullets with grease grooves is to use their grooving tool which does not cut grooves but rather makes them by displacing material. The good news is this does not change the mass of the bullet, the bad news is it means you have to size your bullets after making the grease grooves. Also you are limited to rather shallow grooves.

The proper way to do it would be with a 3-piece die, as I understand they were done in period.

Steve

for what it's worth, i've seen the bullets that have been made on the groove cutter, they are very good bullets. i can't imagine they wouldn't hold enough lube, another option would be the knurl pattern on the bullet, that can hold a ton of lube.

as for the paper patched bullets in the NSSA, i've shot them for years now and never had a problem. frankly it's not possible to have a problem shooting them. I know i'm not a skirmisher (yet) but i don't understand the rule forbidding them.

[Gary Van Kauwenbergh, 101]

I thought Maillemakers video was fascinating, but I really think what you're seeing there is more the effects of aerodynamics than weight imbalance.
Weight imbalance does have an effect, but the real question we need to concern ourselves is ‘How much of an effect does it have in offhand shooting at 100 yards?’ My guess is the argument is more academic than practical.
I do weigh my bullets, but only do it to eliminate the ones that are overly light or heavy. The bullets in the center of the normal range, I keep as ‘match grade’ and use the rest for practice and normal skirmishing.

[Maillemaker]

[quote]I thought Maillemakers video was fascinating, but I really think what you're seeing there is more the effects of aerodynamics than weight imbalance. [quote]

You are probably right.

Steve