There is no magic bullet
There Is No “Magic Bullet”
by Lee Shaver
Every rifle has headspace. It is loosely defined, for the sake of this article, as the space allotted for the cartridge rim to fit it. It is not, as some believe, the amount of excess space left over after the case is inserted. In our single shot rifles with rimmed cases, in most instances it is the distance between the closed breech block face and the forward edge of the cut made in the back of the barrel for the cartridge rim.
This allowance for the cartridge rim is always larger than the rim is thick. There are industry standards as to how much extra there should be, just as there are industry standards as to how thick the rim should be on the cartridge. Every once in a while I get a call from someone who thinks they have a headspace problem that is affecting the accuracy of their rifles. The stories are always about the same…some gunsmith, or the manufacturer has obviously chambered the rifle too deep because the primer is sticking out the back of the case after it has been fired. I usually tell them politely that this is a good thing and will not affect the accuracy of the rifle unless it is well beyond industry standards, and then go on to explain it to them this way.
As the firing pin travels forward and makes contact with the primer it can or will push the cartridge forward in the chamber till the rim touches the forward cut in the chamber. How much or if it actually moves the case depends on many things such as the diameter and speed of the firing pin, hardness of the primer, weight of the loaded case, and whether it is already touching something that will prevent its forward travel such as the bullet being engraved into the rifling, ect.
As the primer ignites, it begins to create a flash fire and gases that expand and build up pressure inside the primer pocket and jet out into the powder charge. This pressure can be enough to begin dislodging the primer and push it rearward towards the breech block face. Once the powder charge ignites and adds the expanding gases of the main charge to the pressure created by the primer, the primer is sure to move to the rear at a high rate of speed like a projectile. I have seen a few soft breechblocks damaged over the years by the impact of primers against them.
Once the primer has traveled to the rear as far as the face of the breech block then the pressure within begins to cause it to act like a hydraulic jack that forces the cartridge case forward in the chamber as far as it will go. As the pressure in the cartridge continues to build, the brass case will swell out until it makes contact with the chamber walls. This contact will seal the chamber pressure inside the rifle and prevent any leakage out the back. It also causes the case to hold onto the chamber to the extent that the case will not slip to the rear and reset the primer in the primer pocket. So it leaves the primer sticking out of the back of the case.
The situation is different with high powered smokeless powder cartridges as they build up enough pressure to cause the case to stretch to the rear until the primer resets. The forward half still clings to the chamber walls and does not move. So when the case stretches to the rear it stretches the overall length of the case and creates a weak spot in the rear middle part of the case that will crack and separate after a few loadings. The case also applies quite a bit of pressure to the bolt face on a high power rifle requiring that the bolt face and locking lugs, etc. be perfectly true and fitted for best accuracy.
Straight-walled black powder-loaded cartridges do not create enough pressure to stretch a case to the rear except in rare instances. There are some cartridges that have enough taper and/or chambers that are slick enough that the case can not get a good hold on the chamber and the case will slip to the rear under pressure and reset the primer, but that is an entirely different process than the high power smokeless cartridges go through. If a black powder cartridge case is stretching when fired it is invariably because the case has been annealed too much and is too soft, or the front of the case is trying to follow the bullet up the bore, but I will address that later.
If everything goes as it should to this point, the primer will be left hanging out of the rear of the primer pocket more or less exactly the amount of the headspace minus the thickness of the rim. This is actually a good thing. Not that you want it hanging out a bunch, but it is a sign that the case is holding in the chamber as it should. When it works right, you don’t have to worry about truing cartridge case rims, squaring breech block faces to perfectly square with the bore or any of the things smokeless powder target rifle guys do to tune their actions for accuracy.
I have a load for my 45-100 that pushes a 550 grain bullet out the muzzle at 1500 fps, and it leaves the primers sticking out just the slightest amount, and the cases never stretch unless I send the front half of the case up the bore with a bullet. That rifle was built from one of the most inexpensive Sharps actions you can buy. The breechblock was never trued to the bore, the firing pin was never bushed (it is still about 1/8 inch in diameter), and that rifle simply shoots as good as any I have ever shot.
Now, let’s leave the rear of the case and move up front where the important stuff is going on. Since we left that back end of the case with the powder burning and pressure building to the point where the case is swelled up to seal the chamber, it is important to know that the soft lead bullets we use react differently than the jacketed bullets with smokeless powder. With smokeless powder and jacketed bullets that pressure builds slower than with black powder, and the case swells and, in theory, the case neck swells and releases the bullet to travel forward. Or perhaps the bullet slips out of the case neck under pressure and begins its forward travel before the case is fully swelled to seal the chamber. It doesn’t really matter for our story here, but if you are shooting with smokeless powder and you are getting smoky cases on the outside or a puff of gases out the breech with light loads, then the case has certainly not sealed the chamber before the bullet heads down the barrel and your brass is too hard or your powder charge too light.
The important differences are that with soft lead bullets and black powder the pressure hits the base of the bullet hard enough that the bullet begins to swell. The laws of physics are simple at this point. The last time I checked, the laws of physics tell us that any object that is at rest tends to stay at rest unless or until it is acted upon by some force. That bullet is just laying there in your chamber and when the pressure hits it the bullet is soft enough that the rear of the bullet begins to move forward, but the strength of the lead is simply not able to withstand the forces being applied to it to move the entire bullet, so the base will swell up until it contacts the inside of the neck of the case which in turn is swelling out to fit the chamber walls. All the while the front of the bullet is still tending to remain at rest. This swelling of the bullet out to fit whatever is surrounding it continues until the nose of the bullet has finally overcome the inertia of being at rest and then the swelling or obturation of the bullet will stop. Imagine hitting a marshmallow with a ping pong paddle and you might get the idea.
How hard that bullet presses against the inside of the chamber, how far up the side of the bullet the swelling takes place, and for what distance up the barrel it is still possible depends on many factors such as granulation of powder, burn rate of powder, hardness and alloy of the bullet and the overall length of the bullet in relation to its diameter, etc.
In my experience, the alloys we most often see in black powder cartridge rifle shooting of approximately 30-1 to 20-1 lead to tin ratios will obturate fully to the diameter of the chamber if allowed and to full depth of the rifling all the way forward to the point where the ogive of the bullet nose starts towards the nose of the bullet. I use 20-1 alloys in my long-muzzleloader and the entire bullet will swell .008″ in diameter to the bottom of the rifling grooves. This happens not only in larger calibers and heavier loads, I have documented, it also happens in light loaded 40-65 silhouette rifles with 20-1 alloys and bullets cast from wheel weights.
Many of the muzzle loading and breech loading match rifle shooters of the 1870s used harder bullets than we do today. At least one English shooter and experimenter of the era wrote how he really preferred a bullet that was hard enough it would only obturate full diameter for the rear 1/3 to 1/2 of its length, and he settled on a bullet of about 10-1 or 12-1 alloy. He was of the opinion that the harder lead would not transfer as much energy outward towards the surface of the barrel and therefore not create as much friction on the bore and believed that it gave him higher velocities. Considering the devices they used to find bullet velocities in those days I do not know if he was truly getting higher velocities that could not be explained by the fact that a harder bullet is lighter, and a lighter bullet accelerates quicker with the same amount of powder, but he certainly proved that it made his rifle shoot flatter to 1,000 yards.
The simple fact that he claimed the harder bullet shot flatter at long range is actually significant. You see there is a lot going on during the time in which the bullet is obturating, not the least of which is that the bullet gets shorter and the nose slumps a little making the nose shorter and fatter. The harder bullet would retain the shape of its nose better and perhaps fly better through the air. But you need to remember that at the lower velocities at the longer distances the nose shape matters little, so I will leave his claims as they stand at this time until I get a chance to fully repeat his tests with modern technology.
There is so much going on during this obturation period that I could actually do an entire article on just that and not cover all of it. So I will cover it as briefly as I can without laying out all of the experiments I and others have done over the 150 years to backup discussion on the matter. It has been recognized as a pivotal point in rifle accuracy for well over a hundred years, and while it was not always understood, at least most of the problems were bypassed by breech seating or muzzle loading bullets in cartridge riflesa practice that is common among Schuetzen shooters, and was at one time fairly common among the match rifle shooters of the 1870s.
One of the many things I learned while doing studies on obturation is that if a bullet swells up beyond the diameter of the grooves of the barrel; the grease groove typically shows some lead to have been dragged rearward off of the leading edge of the groove (rear edge of the band), so the forward edge of the grease groove tends to look like an umbrella. This umbrella effect is simply the displacing of the oversized bullet to the rear as it passes into the bore. These same bullets will also always show some cupping to the bases where the displaced lead has flowed to the rear and left the bullet base stretched to the rear around the outside edge.
If the chamber itself is not oversized but has a gap at the end of the case mouth, then the first grease groove to pass over the gap will show this umbrella effect and the rest of the bullet will pass unharmed. The reason is simple. As the first grease groove passes over the gap at the end of the chamber, the bullet simply crushes shorter in this first grease groove and forces grease out of that groove to fill the gap and the remainder of the bullet passes over the gap filled with grease, and can not bulge into the gap. Any time you have a bit more gap than you would like at the end of the case all you have to do is load the bullet so a grease groove spans the gap and the bullet will shorten a little at that groove and be otherwise unharmed. This little trick works with gaps up to the width of the grease groove, or at least the capacity of the grease held in the groove to fill that gap.
I often hear shooters say that they have not found a bullet that their rifle likes, or that they have started the process of testing all the molds they have, to find out which bullet this rifle likes, or any number of other versions of the same thought process. That thought being that some rifles will shoot better with certain bullet shapes, or weights, or diameters than it will with others. Or that just because the last rifle shot good with this bullet does not mean that this one will.
The simple truth is that there is no magic bullet.
It is true that some bullets will not shoot well in any rifle because of a poor design, or that some bullets shoot well in almost every rifle because it is a great design, but the vast majority of them will shoot better than the shooter if they are fitted, cast, sized, loaded, and managed properly. Some bullets will even be better than others for certain things such as a heavy bullet will be better at longer ranges than a light one because it retains velocity better, but all good bullets will shoot well when loaded properly.
I have a few bullet molds I use for my personal rifles and I always use them to test customer rifles with also. They never fail to shoot well in any rifle I have put them in. Many times we have shot a test group with a new rifle and send the target along with the rifle, and it may take years for the customer to get close to the group we shot with the first try.
Another simple truth is that a bullet that exits the barrel balanced will fly well, and an unbalanced bullet will not. My molds are designed so that they fit properly and do not deform during the obturation process, and remain balanced. If a bullet is out of balance when loaded or has to obturate excessively, or if anything else happens to it during the trip down the bore to throw it out of balance in the least amount it simply will not fly straight.
A number of years ago I had a fellow call me and wanted to discuss his accuracy problems with me. Unfortunately I have never figured out how to charge for a consultation, so I just sat down and gave him a half hour of my time as we discussed his groups, loading techniques, etc. I finally declared that I was certain that his bullets were not coming out of the barrel balanced and most likely they were not going in balanced. After discussing it with him further for a while he began to understand what I was talking about. I received a follow up call a few days later and his rifle was shooting great. It turns out that he worked in a high tech machine shop in management or something, and he took some of his bullets to the inspection crew or one of the machinists, and they built a collet to hold it in while inspecting it with indicators. They became convinced that the minor diameter of the grease grooves was not running true to the outside diameter of the bullet.
They then put a few of them in a lathe and machined the grease grooves to match perfectly with the outside diameter of the bullet. When he tested these bullets the groups were shrunk to right near one minute of angle if I remember correctly. By cutting the grooves to be true with the outside diameter they brought the bullets into a state of being balanced when they went into the rifle which tends to make it a lot easier to be balanced when it comes out.
I once designed a scale to test how far out of balance a bullet was. With that scale we tested a number of molds and found that occasionally you will run into a production mold that just will not throw a balanced bullet no matter what you do. We once tested several production grade molds by the same maker and the same design and located one that threw unbalanced bullets. When we tested those same bullets by shooting them we also found that the bullets from that mold did not shoot nearly as well as the other molds. That is exactly what happened to the fellow mentioned above.
The closest thing there is to a magic bullet is one that is balanced and made to fit the spot it sets in. By that I mean a bullet that is custom made for where it will be when the powder ignites.
I found long ago, after about a year of experimenting, that the easiest way to get the maximum accuracy out of a black powder cartridge rifle with soft lead bullets is not to size the cases, but simply clean them and load them. This has to be done with the proper bullet though.
I went through so many experiments it would take half a book to describe them and tell you what I learned about what it takes to size a case neck perfectly and what effects that had on group size, only to learn that unsized case necks would give me the same maximum accuracy with no real effort if the bullet was fitted properly.
The proper fit for the bullet is simple really. The portion of the bullet that fits inside the case should be a slip fit into the fired case. Not loose and certainly not very tight. I usually go for about .002″ clearance in the case neck just because they tend to vary a little in diameter due to case wall variations. If your rifle has a free bore forward of the chamber like my 45-100 then the portion of the bullet that sets in the free bore should have minimum clearance, and if your bullet has a bore riding section that slips in on top of the rifling, that portion of the bullet should also have minimal clearance to the top of the rifling. If you have a long tapered throat leading into the rifling you could also have the bullet tapered at that point to match the throat angle.
I mentioned minimal clearance instead of designating a clearance because the clearance can vary a little depending on your style of shooting. If you shoot dirty with a blow tube, the clearance of the bullet for any place that might have fouling on it will be about .002″ or slightly more. If you prefer to clean between shots and will not have any fouling present then you can get by with as little as .001″ clearance or less.
The whole idea is that the bullet is going to bump up to fit the spot it is in anyway, so if you fit it as nearly as possible to its final bumped diameter the bullet will be much less likely to become damaged and thrown out of balance during the obturation process. A bullet that is fitted properly and centered in the bore as best as can possibly be done prior to obturation will have the best possibility of fine accuracy because it is most likely to remain balanced.
Stay away from gimmick bullets that have undersized noses and scraper bands, or production molds that have noses small enough that you can stick them nose first into the muzzle of the rifle and wiggle the bullet around. In fact the bullet nose should always be checked to see how it fits the bore at the muzzle when you are using production molds. It should slip in to the muzzle but only be loose enough you can rotate it easily in the bore. If the bullet goes in up to the first driving band and then wobbles it may have problems with consistent obturation. If it goes in with some resistance and will not turn in the bore then it will probably hang up on fouling when used with a blow tube.
The next thing you need to learn about soft bullets and obturation is that as it bumps up it compresses all voids and forms around what ever is there at the moment it bumps up. If the bullet has voids inside they will compress, at least in the rear of the bullet where the obturation is complete. Voids in the front of the bullet will most likely not compress, or at least may not compress completely. These voids are caused during casting, and I won’t go into it a great deal as this is a very popular subject for writers to talk about when they broach the subject of bullet balance. I will go so far as to say that it has been proven over and over again that it is possible to cast bullets without voids so the next time you read an article about how there is always a void in every cast bullet please move on to the next article. Here again is a spot where an entire article could be written about how to cast bullets, and I indeed did so for the first time about a decade ago. It is enough to say that if there are voids inside the rear half of the bullet, and the lead moves in to fill those voids the lead may well have to shift off center to fill it and the center of gravity will move along with it.
Actually voids on the outside of the bullet are more common among shooters who have been casting good bullets for a while. The voids I am talking about are the voids in the lube grooves. It is amazing to me to see how many shooters fuss over casting and weighing their bullets and then are rather cavalier about lubing them, or handling them during the loading process. The lube grooves simply must be evenly full with no excess all the way round. If there is a void in the lube as the bullet swells to fit the spot it is in, there is simply nothing there to stop the bullet from swelling up at that point, and it will continue to do so till the void is filled. If the void is only on one side of the bullet the center of gravity will shift as the bullet fills this void.
I have often proven this point by taking bullets that shoot minute of angle or smaller in one group and then swiping my finger across the lube on one side of the bullet at random removing a small amount of lube in the process for the next group, and showing how those bullets will shoot hollow groups of two minutes of angle or more with only that small amount of lube missing.
An extension of that same thought will prove that any excess lube piled high on the lube grooves or more likely on the nose of the bullet will cause the same thing. A simple little swipe of lube on one side of the nose that leaves a little pile of lube deposited there will be enough to ruin the accuracy of a bullet. Think about it for a minute. The obturation happens so fast that lube does not have a chance to move around and even out around the bullet. If you place a thick layer of lube on one side of the bore riding portion of a bullet and load and fire it that way and catch it afterwards as I have done, you will find that the bullet will have rifling marks impressed full depth on the side of the nose of the bullet that was clean while the opposite side of the nose will simply have no rifling marks at all, as it was not allowed to swell up on that side due to the lube.